Method for producing low residual stress steel plate for shipbuilding and offshore engineering

Abstract

The application discloses a production method of a low residual stress steel plate for ships and ocean engineering. The production method comprises sequentially casting blank heating, hot rolling, controlled water cooling, air cooling self tempering and surface treatment processes. In the surface treatment process, the steel plate is subjected to shot blasting or shot peening. During the process, t=k*d+C, P=k1*d+C1 and S=k2*d+C2, wherein t is the time length of shot blasting or shot peening, the unit is min, k is 0.1-0.2 min / mm, C is 5-7 min, P is the shot blasting or shot peening amount, the unit is kg / min, k1 is 0.4-0.6 kg / (min*mm), C1 is 160-200 kg / min, S is the speed of shot blasting or shot peening, the unit is m / s, k2 is 0.1-0.3 m / (s*mm) and C2 is 65-75 m / s. In this way, the performance of the steel plate can be ensured, and the residual stress can be reduced.

Description

Technical Field

[0001] This invention belongs to the field of steel material preparation technology, and relates to a method for producing steel plates for ships and marine engineering, and more particularly a method for producing steel plates with low residual stress. Background Technology

[0002] Steel for shipbuilding and marine engineering plays an indispensable role in modern marine development and shipping, with extremely wide applications. From large ocean-going freighters and luxury cruise ships to deep-sea drilling platforms and offshore wind power facilities, steel for shipbuilding and marine engineering, with its superior strength, toughness, corrosion resistance, and weldability, provides robust structural support for various marine equipment, ensuring its reliability and safety in complex marine environments. As downstream users increase their automation levels, the requirements for steel plates used in shipbuilding and marine engineering are becoming increasingly stringent, particularly regarding the control of residual stress in the steel plates.

[0003] Residual stress is a self-balancing stress generated and maintained within a material due to uneven deformation under the influence of temperature, phase transformation, or external forces. In the production of medium and heavy plates, deformation stress generated during rolling, thermal stress from heating and cooling, and phase transformation stress from cooling all contribute to the presence of residual stress in the finished steel plate. Furthermore, residual stress is also unavoidably generated during subsequent machining, cold deformation, heat treatment, and welding processes.

[0004] Residual stress has a significant negative impact on the performance of steel plates, mainly manifested in poor dimensional stability, reduced processing accuracy, decreased pitting corrosion resistance, and shortened fatigue life. For example: ① If the residual stress is large after the steel plate is flame-cut, it is prone to deformation defects such as warping and lateral bending, which cannot meet the usage requirements; ② When the steel plate is bent and cold-worked, due to the large or uneven distribution of residual stress, wavy or cracked edges may appear, making welding impossible; ③ After the steel plate is welded, large residual stress may cause cold cracks in the weld; ④ After the steel plate is made into structural components, residual stress may lead to stress concentration, which can cause cracking, and during service, pitting corrosion is prone to occur at the stress concentration points.

[0005] Therefore, controlling and reducing residual stress to obtain steel plates with low residual stress is a problem that urgently needs to be solved in the field of steel for shipbuilding and marine engineering. Summary of the Invention

[0006] The purpose of this invention is to provide a low residual stress steel plate for shipbuilding and marine engineering and a method for producing the same.

[0007] To achieve the above-mentioned objective, one embodiment of the present invention provides a steel plate for shipbuilding and marine engineering. The chemical composition of the steel plate, by mass percentage, includes: C 0.05~0.11%, Si 0.09~0.32%, Mn 0.92~1.63%, Cr 0~0.54%, Ni 0~0.39%, Mo 0~0.31%, Cu 0~0.39%, Nb 0.009~0.056%, Ti 0.009~0.021%, Al 0.021~0.049%, P≤0.0180%, S≤0.0060%, O≤0.0025%, N≤0.0048%, H≤0.0002%, with the remainder being iron and unavoidable impurities.

[0008] Preferably, the chemical composition of the steel plate, by mass percentage, also satisfies any one, two, three, or all of the following: ①, ②, ③, and ④:

[0009] ①CEV=C+Mn / 6+(Cr+Mo) / 5+(Cu+Ni) / 15 is 0.227~0.604;

[0010] ②Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15 is 0.107~0.276;

[0011] ③ The Ni / Cu ratio is 0.95~1.05;

[0012] ④5C+Si+Mn+Cr+Ni+Mo+Cu is 1.46~4.13.

[0013] In each formula, the element symbol represents the mass percentage of the corresponding element.

[0014] Preferably, the residual stress of the steel plate is ≤80MPa, and the residual stress difference between any two points at the head, middle, tail, upper and lower parts of the steel plate is ≤30MPa.

[0015] Preferably, the R of the steel plate m For 400~770MPa, R eH ≥235MPa, A5≥17%, R eH / R m ≤0.88, Z-direction reduction of area ≥35%.

[0016] To achieve the above-mentioned objective, one embodiment of the present invention provides a method for producing steel plates for shipbuilding and marine engineering. The chemical composition of the steel plate, by mass percentage, includes: C 0.05~0.11%, Si 0.09~0.32%, Mn 0.92~1.63%, Cr 0~0.54%, Ni 0~0.39%, Mo 0~0.31%, Cu 0~0.39%, Nb 0.009~0.056%, Ti 0.009~0.021%, Al 0.021~0.049%, P≤0.0180%, S≤0.0060%, O≤0.0025%, N≤0.0048%, H≤0.0002%, with the remainder being iron and unavoidable impurities;

[0017] The production method includes sequential steps.

[0018] Billet heating process: soaking temperature is T NbC +(50~125)℃, soaking time ≥25min;

[0019] Hot rolling process: This involves a first-stage rolling, intermediate billet cooling, and a second-stage rolling to obtain steel plates with a thickness d ≥ 6 mm. During the first-stage rolling, the initial rolling temperature T... nr +(20~160)℃, final rolling temperature T nr +(-10~150)℃, the reduction in each pass ≤26mm; during intermediate billet cooling, the intermediate billet thickness is 2.0~2.5 times the target thickness of the steel plate, and the final cooling temperature A r3 +(50~150)℃, cooling time ≥50s; during the second stage of rolling, the initial rolling temperature A r3 +(45~145)℃, final rolling temperature A r3 +(5~80)℃, hold for 8~10s before the last rolling pass;

[0020] Controlling the water cooling process: Inlet water temperature A r3 +(0~75)℃, outlet water temperature B s +(-100~250)℃, cooling rate 3~18℃ / s;

[0021] Air-cooled self-tempering process: The steel plate is air-cooled on a cooling bed;

[0022] Surface treatment process: After the steel plate cools to room temperature, it is surface treated by shot blasting or shot peening. During this process, one, two, or all of the following three conditions must be met: t = k × d + C, P = k1 × d + C1, S = k2 × d + C2; where t is the duration of shot blasting or shot peening in min, k is 0.1~0.2 min / mm, C is 5~7 min, P is the shot blasting or shot peening rate in kg / min, k1 is 0.4~0.6 kg / (min·mm), C1 is 160~200 kg / min, and S is the shot blasting or shot peening speed in m / s, k2 is 0.1~0.3 m / (s·mm), and C2 is 65~75 m / s.

[0023] Among them, T NbC T nr A r3 B s The following formulas are used to calculate the values ​​of each element, and the element symbols in each formula represent the mass percentage of the corresponding element in the billet.

[0024] T NbC =7700 / (3.18-lg(Nb×C 0.87 ))-273.15;

[0025] T nr =887+464C-357Si+6445Nb-644 +890Ti+363Al;

[0026] A r3 =910-203 -11Si-15.2Mn-30Cr-13Ni-40Mo;

[0027] B s =550-160C-10Mn-10Cr-10Ni-5Mo.

[0028] Preferably, the production method further includes a tempering heat treatment step after the surface treatment step: a heating rate of 8~15℃ / min, and a tempering temperature T of B. s +(-105~55)℃, and control the tempering holding time t1 according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥13.7, where t1 is in min.

[0029] Preferably, the thickness d of the steel plate is 6~20mm, and the tempering temperature T is B. s +(-65~55)℃;

[0030] Alternatively, the steel plate thickness d is 20~50mm, and the tempering temperature T is B. s+(-85~35)℃;

[0031] Alternatively, if the thickness d of the steel plate is greater than 50 mm, and the tempering temperature T is B... s +(-105~15)℃.

[0032] Preferably, the production method further includes a post-tempering stacking process after the tempering heat treatment process: after reaching the tempering holding time t1, the tempering is ended and stacking is carried out directly, with a stacking temperature B. s -(210~110)℃, cooling rate 10~30℃ / h, destacking temperature ≤B s -450℃.

[0033] Preferably, the thickness d of the steel plate is 6~20mm, and the shot used for shot blasting or shot peening is a mixture of shot with a diameter of 0.5mm and shot with a diameter of 0.7mm in a mass ratio of (7~8):5;

[0034] Alternatively, the thickness d of the steel plate is 20~50mm, and the shot used for shot blasting or shot peening is a mixture of shot with a diameter of 0.7mm and shot with a diameter of 1.0mm in a mass ratio of (9~11):5.

[0035] Alternatively, if the thickness d of the steel plate is greater than 50 mm, the shot used for shot blasting or shot peening is a mixture of shot with a diameter of 1.0 mm and shot with a diameter of 1.2 mm in a mass ratio of (4~6):5.

[0036] Preferably, the production method further includes a stacking process between the air-cooled self-tempering process and the surface treatment process: the steel plate is sandwiched between two auxiliary steel plates and stacked in a layered manner of auxiliary steel plate-steel plate-auxiliary steel plate, the stacking temperature of the auxiliary steel plates being M. s +(-110~50)℃, the stacking temperature of the steel plates is M s -(270~160)℃, destacking temperature not exceeding M s -(400~240)℃.

[0037] Preferably, in the air-cooled self-tempering process: the temperature B of the upper cooling bed s +(-150~200)℃, lower cooling bed temperature M s -(260~150)℃.

[0038] Preferably, during the second stage of rolling, the reduction in each pass is ≤20mm, the reduction in the last pass is ≤3mm, and the rolling pause is 8~10s before rolling.

[0039] Preferably, the production method further includes one, two, three, or all of the following four steps:

[0040] In the temperature-controlled preheating and straightening process between the hot rolling process and the controlled water cooling process: at least one preheating and straightening pass is performed, with a straightening speed of 0.1~1.5 m / s and a straightening temperature A. r3 +(3~77)℃, maximum reduction ≤4mm;

[0041] In the temperature-controlled hot straightening process between the water-cooling process and the air-cooled self-tempering process: 1-3 passes of hot straightening are performed, with a straightening speed of 0.1-1.5 m / s and a straightening temperature B. s +(-125~225)℃, maximum reduction ≤4mm;

[0042] The temperature-controlled straightening process between the air-cooled self-tempering process and the surface treatment process involves 2-4 passes of secondary temperature straightening, with a straightening speed of 0.1-0.5 m / s and a straightening temperature M. s -(270~150)℃, maximum reduction ≤10mm;

[0043] The temperature-controlled cold straightening process, between the temperature-controlled straightening process and the surface treatment process, involves 1-3 passes of cold straightening at a speed of 0.1-0.5 m / s and a straightening temperature of M. s -(420~360)℃, maximum reduction ≤6mm;

[0044] Among them, M S The following formula is used for calculation, with the unit being ℃. The element symbols in the formula represent the mass percentage of the corresponding element in the billet.

[0045] M S =539-423C-11Si-30.4Mn-12.1Cr-17.7Ni-7.5Mo.

[0046] Preferably, the chemical composition of the steel plate, by mass percentage, also satisfies any one, two, three, or all of the following conditions:

[0047] CEV = C + Mn / 6 + (Cr + Mo) / 5 + (Cu + Ni) / 15 is 0.227~0.604;

[0048] Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15 is 0.107~0.276;

[0049] The Ni / Cu ratio is 0.95~1.05;

[0050] 5C+Si+Mn+Cr+Ni+Mo+Cu is 1.46~4.13;

[0051] In the formula, the element symbols represent the mass percentage of the corresponding element.

[0052] Preferably, the billet heating process includes heat recovery, preheating, primary heating, secondary heating and homogenization. The heat recovery temperature is ≤800℃, the preheating temperature is ≤900℃, the primary heating temperature is 970~1030℃, the secondary heating temperature is 1070~1130℃, and the total heating time is 0.019~0.023h / mm billet thickness.

[0053] Preferably, in the billet heating process, the billet's furnace entry temperature is ≥ M. S -350℃, M S The following formula is used for calculation, with the unit being ℃. The element symbols in the formula represent the mass percentage of the corresponding element in the billet.

[0054] M S =539-423C-11Si-30.4Mn-12.1Cr-17.7Ni-7.5Mo.

[0055] Compared with the prior art, the beneficial effects of one embodiment of this application are as follows:

[0056] On the one hand, the chemical composition does not contain expensive alloys such as V, and the content of alloys such as Cr, Ni, and Mo is low, resulting in lower production costs;

[0057] On the other hand, by adopting a low-carbon manganese, phosphorus, and sulfur + micro-niobium, titanium, nickel, and copper low-alloy low-stress composition system design, and combining it with the homogenization temperature, homogenization time, temperature, reduction and residence time during hot rolling, control of water cooling temperature and cooling rate, and surface treatment operations, not only can the mechanical properties, low-temperature performance and weldability of the steel plate be guaranteed, but also the residual stress of the steel plate can be greatly reduced and the uniformity of residual stress distribution can be improved. This overcomes the defects caused by residual stress in existing steel plates, such as performance degradation, poor processing performance and short service life, and improves the applicability of steel plates in shipbuilding and marine engineering. Attached Figure Description

[0058] Figure 1 This is a metallographic diagram of the steel plate of Experimental Example 1 of the present invention;

[0059] Figure 2 This is a metallographic diagram of the steel plate of Experimental Example 1A of the present invention;

[0060] Figure 3 This is a metallographic diagram of the steel plate of Experimental Example 1B of the present invention;

[0061] Figure 4 This is a metallographic diagram of the steel plate of Experimental Example 1C of the present invention;

[0062] Figure 5 This is a metallographic diagram of the steel plate of Experimental Example 1D of the present invention;

[0063] Figure 6 This is a metallographic diagram of the steel plate of Experimental Example 1E of the present invention;

[0064] Figure 7 This is a metallographic diagram of the steel plate of Experimental Example 1F of the present invention. Detailed Implementation

[0065] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them.

[0066] One embodiment of the present invention provides a steel plate for ships and marine engineering.

[0067] The chemical composition of the steel plate, by mass percentage, includes: C 0.05~0.11%, Si 0.09~0.32%, Mn 0.92~1.63%, Cr 0~0.54%, Ni 0~0.39%, Mo 0~0.31%, Cu 0~0.39%, Nb 0.009~0.056%, Ti 0.009~0.021%, Al 0.021~0.049%, P≤0.0180%, S≤0.0060%, O≤0.0025%, N≤0.0048%, H≤0.0002%, with the remainder being iron and unavoidable impurities.

[0068] The following is a detailed analysis and explanation of the main functions of each element and the selection of its dosage.

[0069] C: Carbon is the most economical strengthening element in steel, providing solid solution strengthening. It also forms carbides with niobium, titanium, chromium, molybdenum, etc., providing precipitation strengthening. Increased carbon content increases the material's hardness and strength, but reduces ductility and toughness. During quenching or rapid cooling, the formation of carbides and martensite causes significant volume expansion, thus increasing residual stress. Higher carbon content leads to greater hardenability of the steel and a greater tendency for residual stress to concentrate. In this invention, the carbon content is controlled at 0.05~0.11%.

[0070] Preferably, the carbon content can be controlled at any one of 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, and 0.11%.

[0071] Silicon (Si): As a deoxidizer and solid solution strengthening element, silicon can improve the strength and hardness of steel, but it reduces plasticity and toughness. The addition of silicon increases the elastic limit and yield strength of steel, but has little direct impact on residual stress. High silicon content increases grain boundary segregation of elements such as phosphorus and sulfur, reducing low-temperature toughness and weldability. Furthermore, excessive silicon easily forms Fe2SiO4 on the surface of continuously cast billets, which is detrimental to the control of steel plate surface quality. In one embodiment, the silicon content is controlled at 0.09~0.32%.

[0072] Preferably, the silicon content can be controlled at any one of 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.30%, 0.31%, and 0.32%.

[0073] Mn: Manganese plays a solid solution strengthening role in steel, improving its hardenability and strength. However, increasing manganese content increases residual stress, especially during rapid cooling. Excessive manganese can lead to center segregation in the cast billet, negatively impacting toughness and increasing the banding level, resulting in a more uneven microstructure. Furthermore, manganese readily combines with sulfur to form manganese sulfide inclusions. Center segregation, banding, and inclusions all increase residual stress in the steel. In one embodiment, the manganese content is controlled at 0.92~1.63%.

[0074] Preferably, the manganese content can be controlled at any one of 0.92%, 0.94%, 0.95%, 0.98%, 1.00%, 1.03%, 1.05%, 1.07%, 1.10%, 1.13%, 1.16%, 1.18%, 1.20%, 1.22%, 1.24%, 1.25%, 1.30%, 1.31%, 1.33%, 1.35%, 1.37%, 1.39%, 1.40%, 1.45%, 1.46%, 1.48%, 1.50%, 1.51%, 1.52%, 1.54%, 1.55%, 1.57%, 1.59%, 1.60%, 1.61%, and 1.63%.

[0075] Cr: Chromium plays a solid solution strengthening role in steel, significantly improving its hardenability and hardness. Chromium can form stable carbides and improve the stability of martensite, resulting in significant residual stress after quenching or rapid cooling. When the chromium content is too high, the distribution of residual stress after cooling becomes more complex. In this application, chromium can be selectively added or selectively omitted. Specifically, the chromium content is controlled at 0~0.54%.

[0076] Preferably, in one embodiment, chromium is not present, that is, the chromium content is 0 or close to 0. For example, chromium alloys are not actively added in the form of alloying during the production process so that the chromium content in the steel is 0, or chromium is introduced as an impurity in the raw materials.

[0077] Preferably, in another embodiment, chromium is added, and the chromium content can be controlled at 0.06~0.54%.

[0078] Preferably, the chromium content can be controlled within any one of 0.06%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.15%, 0.20%, 0.22%, 0.25%, 0.27%, 0.29%, 0.32%, 0.33%, 0.36%, 0.39%, 0.41%, 0.45%, 0.47%, 0.50%, 0.53%, and 0.54%.

[0079] Ni: Nickel plays a solid solution strengthening role in steel, increasing its strength without significantly increasing its hardness. Nickel expands the austenite phase region, thereby reducing residual stress; furthermore, nickel can improve the toughness of steel and reduce stress concentration. In this application, nickel may be selectively added or not added. Specifically, the nickel content is controlled at 0~0.39%.

[0080] Preferably, in one embodiment, nickel is not present, that is, the nickel content is 0 or close to 0. For example, nickel alloys are not actively added in the form of alloying during the production process so that the nickel content in the steel is 0, or the nickel is introduced as an impurity in the raw materials.

[0081] Preferably, in another embodiment, nickel is added, with the nickel content controlled at 0.06~0.39%.

[0082] Preferably, the nickel content can be controlled at any one of 0.06%, 0.08%, 0.10%, 0.11%, 0.12%, 0.16%, 0.18%, 0.20%, 0.22%, 0.24%, 0.27%, 0.29%, 0.30%, 0.33%, 0.34%, 0.36%, and 0.39%.

[0083] Mo: Molybdenum can significantly improve the hardenability of steel, as well as its strength and toughness. It also refines grain size and improves corrosion resistance. Molybdenum can improve the tempering stability of steel and reduce the increase of residual stress. In this application, molybdenum may be selectively added or not added. Specifically, the molybdenum content is controlled at 0~0.31%.

[0084] Preferably, in one embodiment, molybdenum is not present, that is, the molybdenum content is 0 or close to 0. For example, molybdenum alloys are not actively added in the form of alloying during the production process so that the molybdenum content in the steel is 0, or the molybdenum is introduced as an impurity in the raw materials.

[0085] Preferably, in another embodiment, molybdenum is added, and the molybdenum content is controlled at 0.02~0.31%.

[0086] Preferably, the molybdenum content can be controlled at any one of 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.08%, 0.12%, 0.14%, 0.16%, 0.18%, 0.20%, 0.22%, 0.25%, 0.27%, 0.29%, and 0.31%.

[0087] Cu: Copper promotes the precipitation of niobium and can compensate for the strength loss caused by the decrease in carbon content. Copper mainly exists in steel in a solid solution state. During tempering, it can precipitate as ε-Cu, which has a relatively small impact on residual stress. In this application, copper can be selectively added or not added. Specifically, the copper content is controlled at 0~0.39%.

[0088] Preferably, in one embodiment, copper is not present, that is, the copper content is 0 or close to 0. For example, copper alloys are not actively added in the form of alloying during the production process so that the copper content in the steel is 0, or copper is introduced as an impurity in the raw materials.

[0089] Preferably, in another embodiment, copper is added, and the copper content is controlled at 0.06~0.39%.

[0090] Preferably, the copper content can be controlled at any one of 0.06%, 0.08%, 0.11%, 0.15%, 0.20%, 0.21%, 0.23%, 0.25%, 0.29%, 0.30%, 0.33%, 0.34%, 0.36%, and 0.39%.

[0091] Niobium (Nb) is an important grain-refining element in steel. During hot rolling, niobium strongly inhibits austenite recrystallization and precipitation within austenite, pinning austenite grain boundaries and refining recrystallized grains. During cooling, dissolved niobium can continue to precipitate as niobium carbonitrides, significantly refining the microstructure after phase transformation and further improving the strength and toughness of the steel. Niobium can reduce residual stress through grain refinement and precipitation strengthening. In this application, the niobium content is controlled at 0.009~0.056%.

[0092] Preferably, the niobium content can be controlled at any one of 0.009%, 0.010%, 0.014%, 0.015%, 0.018%, 0.019%, 0.021%, 0.024%, 0.026%, 0.030%, 0.031%, 0.034%, 0.036%, 0.038%, 0.040%, 0.042%, 0.044%, 0.046%, 0.048%, 0.050%, 0.054%, and 0.056%.

[0093] Ti: Titanium is a nitrogen-fixing element in steel. It can form dispersed carbonitrides, which inhibit austenite grain coarsening and refine grains during billet heating and hot rolling, thereby reducing residual stress. However, when the titanium content is high, large carbonitride precipitates are easily formed in the core of the billet, affecting the low-temperature toughness of the steel plate. Furthermore, large TiN particles can easily lead to stress concentration. In this application, the titanium content is controlled at 0.009~0.021%.

[0094] Preferably, the titanium content can be controlled at any one of 0.009%, 0.010%, 0.014%, 0.015%, 0.016%, 0.018%, 0.020%, and 0.021%.

[0095] Al: Aluminum is a deoxidizing element in steel. Excessive aluminum can increase the number of Al2O3 inclusions in steel, affecting its low-temperature toughness. Furthermore, large inclusions can lead to discontinuous microstructure and stress concentration. In this application, the aluminum content is controlled at 0.021~0.049%.

[0096] Preferably, the aluminum content can be controlled at any one of 0.021%, 0.025%, 0.028%, 0.030%, 0.033%, 0.035%, 0.038%, 0.040%, 0.042%, 0.045%, 0.047%, and 0.049%.

[0097] P, S, N, O, and H are all impurity elements in steel that can cause deterioration in the properties of steel plates, including but not limited to increased residual stress. In this application, P is controlled to be ≤0.0180%, S ≤0.0060%, O ≤0.0025%, N ≤0.0048%, and H ≤0.0002%.

[0098] Preferably, the P content is controlled at 0.0150% or less, 0.0120% or less, or even 0.0050% or more.

[0099] Preferably, the sulfur content is controlled at 0.0050% or less, 0.0040% or less, or even 0.0005% or more.

[0100] Preferably, the nitrogen content is controlled at 0.0022% or more.

[0101] Preferably, the O content is controlled at 0.0011% or more.

[0102] Preferably, the H content is controlled at 0.00018% or less, and can also be controlled at 0.00005% or more.

[0103] Furthermore, the chemical composition of the steel plate, by mass percentage, also satisfies any one, two, three, or all of the following: ①, ②, ③, and ④:

[0104] ①CEV=C+Mn / 6+(Cr+Mo) / 5+(Cu+Ni) / 15 is 0.227~0.604;

[0105] ②Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15 is 0.107~0.276;

[0106] ③ The Ni / Cu ratio is 0.95~1.05;

[0107] ④5C+Si+Mn+Cr+Ni+Mo+Cu is 1.46~4.13.

[0108] In each formula, the element symbol represents the mass percentage of the corresponding element. For example, if the content of element C in the steel plate is 0.05%, then "C" in the formula represents a mass percentage of 0.05.

[0109] Furthermore, the residual stress of the steel plate is ≤80MPa.

[0110] More preferably, the residual stress of the steel plate does not exceed 70 MPa, or does not exceed 60 MPa, or does not exceed 50 MPa, or does not exceed 40 MPa, or does not exceed 30 MPa.

[0111] Furthermore, the steel plate exhibits small fluctuations and uniform distribution of residual stress throughout the plate.

[0112] For example, the residual stress difference between any two points in the head, middle, tail, upper, and lower parts is ≤30MPa.

[0113] In this application, the steel can be sampled and subjected to residual stress testing in accordance with GB / T 31310-2014 "Determination of Residual Stress in Metallic Materials - Drilling Strain Method".

[0114] In this embodiment, the thickness d of the steel plate is ≥ 6 mm.

[0115] Furthermore, the steel plate possesses excellent mechanical properties:

[0116] R m The pressure ranges from 400 to 770 MPa.

[0117] R eH ≥235MPa;

[0118] A5≥17%;

[0119] R eH / R m ≤0.88;

[0120] Z-direction reduction of area ≥35%.

[0121] In this application, the steel can be sampled and its mechanical properties tested in accordance with GB / T 2975-2018 "Sampling location and specimen preparation for mechanical property testing of steel and steel products" and GB / T 228.1-2021 "Metallic materials, tensile testing - Part 1: Room temperature test method".

[0122] The steel plate has excellent toughness and satisfies any one or any combination of the following conditions:

[0123] Impact energy at 20℃ KV2≥300J;

[0124] Impact energy at 0℃ KV2≥250J;

[0125] Impact energy at -20℃ KV2≥220J;

[0126] Impact energy at -40℃ KV2≥200J;

[0127] -60℃ impact energy KV2≥180J;

[0128] At 0℃, the crack tip opening displacement of CTOD is ≥0.5mm;

[0129] At -20℃, the crack tip opening displacement of CTOD is ≥0.3mm;

[0130] At -40℃, the crack tip opening displacement of CTOD is ≥0.2mm.

[0131] In this application, the steel can be sampled and its low-temperature performance tested in accordance with GB / T 2975-2018 "Sampling Location and Sample Preparation for Mechanical Property Testing of Steel and Steel Products" and GB / T 229-2020 "Charpy Pendulum Impact Test Method for Metallic Materials".

[0132] In addition, the steel plate has excellent shape, with an unevenness of ≤3mm / m.

[0133] Furthermore, the microstructure of the steel plate is polygonal ferrite + pearlite + tempered bainite, and the total volume percentage of polygonal ferrite, pearlite and tempered bainite is 100%.

[0134] In one embodiment, the total volume percentage of polygonal ferrite and pearlite is 95% to 100%, and the volume percentage of tempered bainite is 0% to 5%. That is, the microstructure of the steel plate can be only polygonal ferrite and pearlite, or it can contain a small amount of tempered bainite.

[0135] In another embodiment, the volume percentage of tempered bainite is relatively large, ranging from 60% to 93%; the total volume percentage of polygonal ferrite and pearlite is less than 40%.

[0136] Among them, polygonal ferrite accounts for 85-97% of the volume, pearlite accounts for 3-10% of the volume, tempered bainite accounts for 0-10% of the volume, and the total volume of polygonal ferrite, pearlite and tempered bainite is 100%.

[0137] The average grain size of the steel plate is 4~35μm.

[0138] Furthermore, one embodiment of the present invention also provides a method for producing the steel plate. This method can be used to prepare a steel plate with low residual stress for shipbuilding and marine engineering.

[0139] The production method includes a sequential process of billet heating, hot rolling, controlled water cooling, air cooling and self-tempering, and surface treatment to process the billet into the steel plate.

[0140] The following sections will describe each process in detail in order.

[0141] <Bill Heating Process>

[0142] In this process, the billet is sent into a heating furnace for heating.

[0143] The billet can be either a continuously cast billet or a mold-cast billet; this application does not specify either.

[0144] The thickness of the cast billet is preferably above 200mm, for example, 220~320mm.

[0145] The chemical composition of the billet is consistent with that of the steel plate prepared therefrom.

[0146] In this process, the soaking temperature is T. NbC +(50~125)℃, heat soaking time ≥25min.

[0147] T NbC The initial precipitation temperature of NbC is given by the formula T. NbC=7700 / (3.18-lg(Nb×C 0.87 The formula ))-273.15 is used for calculation, where the element symbols in the formula represent the mass percentage of the corresponding element in the billet.

[0148] Thus, by controlling the homogenization temperature and duration, on the one hand, excessive growth of austenite grains can be avoided, preparing for precipitation in subsequent hot rolling processes; on the other hand, and more importantly, it can ensure that Nb precipitates are completely dissolved, reducing residual stress.

[0149] Preferably, the heat spreader temperature is T. NbC +50℃, T NbC +55℃, T NbC +60℃, T NbC +70℃, T NbC +80℃, T NbC +90℃, T NbC +100℃, T NbC +110℃, T NbC +115℃, T NbC +120℃, T NbC Any value of +125℃.

[0150] Preferably, this process can employ segmented heating, such as including heat recovery, preheating, primary heating, secondary heating, and homogenization. However, it is not limited to this.

[0151] The heat recovery temperature is ≤800℃, the preheating temperature is ≤900℃, the first heating temperature is 970~1030℃, the second heating temperature is 1070~1130℃, and the total heating time is 0.019~0.023h / mm billet thickness. In this way, by segmenting the heating process and controlling the temperature of each segment, the billet can be heated slowly and uniformly, reducing the temperature difference between the beginning, middle, and end of the billet, as well as the surface and center, thereby avoiding cracking caused by thermal stress.

[0152] Furthermore, the furnace entry temperature of the billet is ≥ M S -350℃.

[0153] M S The starting temperature for the austenite-to-martensite phase transformation is given by formula M. S =539-423C-11Si-30.4Mn-12.1Cr-17.7Ni-7.5Mo, calculated in °C. The element symbols in the formula represent the mass percentage of the corresponding element in the billet.

[0154] <Hot Rolling Process>

[0155] In this process, the billet is rolled into a steel plate with a thickness d≥6mm through a first-stage rolling, intermediate billet cooling, and a second-stage rolling.

[0156] The thickness d of the steel plate is, for example, 6~100mm.

[0157] During the first stage of rolling, the initial rolling temperature T nr +(20~160)℃, final rolling temperature T nr +(-10~150)℃, the reduction in each pass is ≤26mm.

[0158] Among them, T nr The minimum temperature for austenite recrystallization is given by formula T. nr =887+464C-357Si+6445Nb-644 The calculation is performed using +890Ti+363Al, and the element symbols in each formula represent the mass percentage of the corresponding element in the billet.

[0159] The thickness of the intermediate billet obtained through the first stage of rolling is 2.0 to 2.5 times the target thickness of the steel plate.

[0160] Thus, rolling in a higher temperature range can reduce the resistance to rolling deformation and increase the rolling reduction, which is conducive to deformation penetrating to the core of the billet and improving defects such as core segregation, porosity and banded structure. Secondly, it ensures that the billet can be rolled in the recrystallization zone to avoid mixed crystals. At the same time, the precipitation of Nb compounds prevents the growth of recrystallized grains and refines the recrystallized grains.

[0161] The target thickness of the steel plate is the final thickness d of the steel plate.

[0162] Preferably, during the first stage of rolling, the initial rolling temperature is T. nr +20℃, T nr +25℃, T nr +30℃, T nr +35℃, T nr +40℃, T nr +45℃, T nr +50℃, T nr +55℃, T nr +60℃, T nr +70℃, T nr +70℃, T nr +90℃, T nr +100℃, T nr +110℃, T nr +120℃, T nr +130℃, T nr +140℃, T nr +150℃, T nr Any value within +160℃.

[0163] Preferably, during the first stage of rolling, the final rolling temperature is T. n -10℃, T nr -5℃, T nr T nr +5℃, T nr +10℃, T nr +2℃, T nr +30℃, T nr +40℃, T nr +50℃, T nr +60℃, T nr +70℃, T nr +80℃, T nr +90℃, T nr +100℃, T nr +110℃, T nr +120℃, T nr +130℃, T nr +140℃, T nr Any value within +150℃.

[0164] Furthermore, during the cooling of the intermediate billet, the intermediate billet is cooled to a final cooling temperature A. r3 +(50~150)℃, cooling time ≥50s.

[0165] Among them, A r3 The temperature at which ferrite (α-Fe) begins to precipitate from austenite (γ-Fe) upon cooling is given by formula A. r3 =910-203 The calculation is performed using the formula -11Si-15.2Mn-30Cr-13Ni-40Mo, where the element symbols in the formula represent the mass percentage of the corresponding element in the billet.

[0166] In this way, by controlling the final cooling temperature and cooling time, not only can production efficiency be guaranteed, but also the rapid growth of recrystallized grains during the waiting period can be avoided, which would lead to a decrease in low-temperature toughness. More importantly, it allows for sufficient recrystallization and releases a certain amount of internal stress at high temperatures.

[0167] Preferably, the final cooling temperature is A. r3 +50℃, A r3 +60℃, A r3 +70℃, A r3 +80℃, A r3 +90℃, A r3 +100℃, A r3 +110℃, A r3 +120℃, A r3 +130℃, A r3 +140℃, A r3 Any value within +150℃.

[0168] Preferably, the cooling time is ≥70s.

[0169] More preferably, the intermediate billet can be cooled by air cooling.

[0170] Next, during the second stage of rolling, the initial rolling temperature A r3 +(45~145)℃, final rolling temperature A r3 +(5~80)℃, hold for 8~10s before the last rolling pass.

[0171] Preferably, during the second stage of rolling, the initial rolling temperature is A. r3 +45℃, A r3 +50℃, A r3 +60℃, A r3 +70℃, A r3 +80℃, A r3 +90℃, A r3 +100℃, A r3 +110℃, A r3 +120℃, A r3 +130℃, A r3 +140℃, A r3 Any value within +145℃.

[0172] Preferably, during the second stage of rolling, the final rolling temperature is A. r3 -5℃, A r3 A r3 +10℃, A r3 +20℃, A r3 +30℃, A r3 +40℃, A r3 +50℃, A r3 +60℃, A r3 +70℃, A r3 Any value within +80℃.

[0173] Thus, by controlling the initial rolling temperature and the final rolling temperature, the microstructure can be optimized; in addition, by pausing for 8 to 10 seconds before the final rolling pass, the stress accumulated in the steel can be fully released, thereby ensuring that low residual stress is ultimately obtained.

[0174] Preferably, during the second stage of rolling, the reduction in each pass is ≤20mm, and the reduction in the last pass is ≤3mm.

[0175] Thus, by using small to medium reduction deformation, a fine microstructure can be obtained during the subsequent cooling process, thereby improving the low-temperature toughness of the steel plate. Furthermore, through the synergistic effect of the final reduction and the dwell time, the plate shape can be improved, the temperature difference between plates can be reduced, and residual stress can be further reduced.

[0176] <Controlled Water Cooling Process>

[0177] In this process, the rolled steel plate is cooled by water.

[0178] In this process, the water inlet temperature A r3 +(0~75)℃, outlet water temperature B s +(-100~250)℃, cooling rate 3~18℃ / s.

[0179] Among them, B s The temperature at which the bainitic phase transformation begins is given by formula B. s =550-160C-10Mn-10Cr-10Ni-5Mo is calculated, where the element symbols in the formula represent the mass percentage of the corresponding element in the billet.

[0180] In this way, by controlling the temperature and cooling rate, the supercooled austenite phase in the steel plate can be cooled to induce a phase transformation. By using a slow cooling rate with weak water, the phase transforms into ferrite / bainite, thereby ensuring a good match and balanced development of strength and toughness; avoiding the formation of martensite; and ensuring low and uniform distribution of residual stress.

[0181] Preferably, the water temperature is A r3 A r3 +10℃, A r3 +20℃, A r3 +30℃, A r3 +40℃, A r3 +50℃, A r3 +60℃, A r3 +70℃, A r3 Any value within +75℃.

[0182] Preferably, the outlet water temperature is B s -150℃, B s -140℃, B s -120℃, B s -100℃, B s -80℃, B s -60℃, B s -40℃, B s -20℃, B s B s +20℃, B s +40℃, B s +60℃, B s +80℃, B s +100℃, B s +110℃, B s +120℃, B s +130℃, Bs +140℃, B s Any value within +150℃.

[0183] Preferably, the cooling rate is any value among 3℃ / s, 4℃ / s, 5℃ / s, 7℃ / s, 8℃ / s, 10℃ / s, 12℃ / s, 14℃ / s, 15℃ / s, 16℃ / s, and 18℃ / s.

[0184] Preferably, in this process, the steel plate is water-cooled using an ultra-fast cooling system.

[0185] The roller speed of the ultra-fast cooling system is preferably controlled at 0.5~1.5m / s.

[0186] Furthermore, in an optional embodiment, the cooling manifold in the ultrafast cooling system can be controlled in an intermittent manner or with head-to-tail shielding. Of course, this application is not limited to this.

[0187] The intermittent method is specifically exemplified by the ultra-fast cooling system, which includes more than 24 sets of cooling manifolds distributed along the roller conveyor. Furthermore, the cooling manifolds are controlled in such a way that, along the roller conveyor, for every 1 to 2 sets of cooling manifolds that are turned on, there are 1 to 2 sets of cooling manifolds that are turned off at intervals.

[0188] The head and tail shielding method is specifically as follows: the steel plate is divided into Xn head low-temperature zones, a middle zone, and Xm tail low-temperature zones from head to tail, where Xn and Xm are positive integers greater than 1; using the cooling water volume Q per unit length in the middle zone as a standard, the cooling water volume per unit length in the Xn head low-temperature zones is controlled to increase sequentially from the head, and each is k times Q. X1 ~k Xn The K values ​​are: times, and the cooling water volume per unit length of the Xm tail-end low-temperature zones increases sequentially from the tail end, with each value being Q. X1 ~K Xm times; where k X1 ~k Xn All values ​​range from 0.55 to 0.85, K X1 ~K Xm The values ​​are all between 0.50 and 0.80.

[0189] For example, Xn and Xm can both be 3, and correspondingly, k X1 k X2 k X3 K takes values ​​of 0.55~0.65, 0.65~0.75, and 0.75~0.85 respectively. X1 K X2 K X3 The values ​​are 0.50~0.60, 0.60~0.70, and 0.70~0.80 respectively.

[0190] <Air-cooled self-tempering process>

[0191] In this process, the steel plate is cooled by air cooling on a cooling bed, during which self-tempering occurs.

[0192] Thus, by water cooling followed by air cooling self-tempering, combined with temperature control on the cooling bed, the steel plate can release phase transformation stress and thermal stress during air cooling self-tempering. On the other hand, air cooling self-tempering can decompose the bainite or MA generated during phase transformation, improve toughness and local hard spots, and further release internal stress.

[0193] Preferably, in this process, the temperature B of the upper cooling bed is... s +(-150~200)℃.

[0194] The temperature of the upper cooling bed is B s -150℃, B s -140℃, B s -120℃, B s -100℃, B s -80℃, B s -60℃, B s -50℃, B s -40℃, B s -10℃, B s B s +10℃, B s +30℃, B s +50℃, B s +60℃, B s +70℃, B s +80℃, B s +90℃, B s +100℃, B s +130℃, B s +150℃, B s +160℃, B s +180℃, B s Any value within +200℃.

[0195] Furthermore, in this process, the temperature of the lower cooling bed for the steel plate does not exceed M. s -150℃.

[0196] Preferably, the temperature of the lower cooling bed is M. s -(260~150)℃.

[0197] More preferably, the temperature of the lower cooling bed for the steel plate is M. s -260℃, M s -240℃, M s -210℃, M s -200℃, M s-190℃, M s -180℃, M s -170℃, M s -160℃, M s Any value within -150℃.

[0198] <Surface Treatment Process>

[0199] After the steel plate is cooled to room temperature, it is surface treated by shot blasting or shot peening.

[0200] During this period, one, two, or all of the following three conditions must be met:

[0201] Condition 1, t=k×d+C;

[0202] Condition 2, P = k1 × d + C1;

[0203] Condition 3: S = k2 × d + C2.

[0204] Where t is the duration of shot blasting or shot peening in min, k is 0.1~0.2 min / mm, C is 5~7 min, P is the shot blasting or shot peening rate in kg / min, k1 is 0.4~0.6 kg / (min·mm), C1 is 160~200 kg / min, S is the shot blasting or shot peening velocity in m / s, k2 is 0.1~0.3 m / (s·mm), C2 is 65~75 m / s;

[0205] Thus, by shot blasting or shot peening the steel plate cooled to room temperature, surface compressive stress can be achieved. This surface compressive stress can then counteract the residual tensile stress inside the steel plate, thereby reducing residual stress and improving its distribution. In particular, by jointly controlling the time t, shot blasting or shot peening amount P, speed S, and plate thickness d, a uniform compressive stress layer can be formed on the surface of the steel plate. The resulting compressive stress can significantly eliminate residual tensile stress, thereby reducing residual stress and improving its distribution.

[0206] Preferably, in one embodiment, for the steel plate with a thickness d of 6 to 20 mm, the shot used for shot blasting or shot peening is a mixture of shot with a diameter of 0.5 mm and shot with a diameter of 0.7 mm in a mass ratio of (7 to 8): 5.

[0207] For the steel plate with a thickness d of 20~50mm, the shot used for shot blasting or shot peening is a mixture of shot with a diameter of 0.7mm and shot with a diameter of 1.0mm in a mass ratio of (9~11):5.

[0208] For the steel plate with a thickness d > 50 mm, the shot used for shot blasting or shot peening is a mixture of shot with a diameter of 1.0 mm and shot with a diameter of 1.2 mm in a mass ratio of (4~6):5.

[0209] Optionally, the shot used may be cast steel shot with a hardness of 35-50 HRC. The specific material of the cast steel shot is not limited in this application.

[0210] Furthermore, the shot blasting or shot peening angle is 45°~80°, with a coverage rate of 100%.

[0211] In summary, one embodiment of the present invention can significantly reduce the residual stress of steel plates and improve the uniformity of residual stress distribution by controlling the homogenization temperature, homogenization time, temperature during hot rolling, water cooling temperature and cooling rate, and surface treatment operations. For example, the residual stress of the steel plate can be ≤80MPa, and the difference in residual stress between any two points at the head, middle, tail, upper, and lower parts can be ≤30MPa.

[0212] As a preferred embodiment, the production method may further include any one, any combination of, or all of the following processes: stacking process, tempering heat treatment process, tempered stacking process, temperature-controlled preheating straightening process, temperature-controlled hot straightening process, temperature-controlled cold straightening process, and temperature-controlled cold straightening process.

[0213] The following sections will provide a detailed introduction to each process.

[0214] <Stacking Process>

[0215] This process is located between the air-cooled self-tempering process and the surface treatment process.

[0216] In this process, the steel plate and the auxiliary steel plate are stacked together.

[0217] Specifically, the steel plate is sandwiched between two auxiliary steel plates and stacked in a layered manner of auxiliary steel plate-steel plate-auxiliary steel plate. That is, the lower surface of the steel plate is completely covered by the lower auxiliary steel plate, and the upper surface of the steel plate is completely covered by the upper auxiliary steel plate.

[0218] The stacking temperature M of the auxiliary steel plates used is... s +(-110~50)℃.

[0219] The stacking temperature of the steel plates is ≤ M s -150℃, destacking temperature not exceeding M s -(400~240)℃.

[0220] Thus, the stacking temperature of the steel plate is lower than that of the auxiliary steel plate. The heat from the auxiliary steel plate can be used to generate a tempering effect on the steel plate. On the one hand, this improves the uniformity of the steel plate's structure and properties. On the other hand, it can further release internal stress, reduce the residual stress of the steel plate, and improve the uniformity of residual stress distribution.

[0221] Preferably, the stacking temperature of the steel plates is M. s -(270~160)℃.

[0222] Preferably, the stacking temperature of the steel plates is M. s -270℃, M s -260℃, M s -250℃, M s -240℃, M s -230℃, M s -220℃, M s -210℃, M s -200℃, M s -190℃, M s -180℃, M s -170℃, M s Any value within -160℃.

[0223] The unstacking temperature of the steel plates shall not exceed M. s -400℃, M s -390℃, M s -380℃, M s -370℃, M s -360℃, M s -350℃, M s -340℃, M s -330℃, M s -320℃, M s -310℃, M s -300℃, M s -290℃, M s -280℃, M s -270℃, M s -260℃ or M s -240℃.

[0224] Furthermore, the length, width, and thickness of the steel plate are all smaller than the length, width, and thickness of the auxiliary steel plate, respectively.

[0225] Furthermore, the stacking time in this process is preferably 12 to 18 hours.

[0226] <Tempering heat treatment process>

[0227] This process occurs after the surface treatment process.

[0228] In this process, the heating rate is 8~15℃ / min, and the tempering temperature T is B. s +(-105~55)℃, and control the tempering holding time t1 according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥13.7, where t1 is in min.

[0229] That is, not only is the tempering temperature T controlled within a certain range, but the tempering temperature T and the tempering holding time t1 are also coordinated and regulated according to the formula. In this way, not only can the microstructure and properties, including mechanical properties, ductility, toughness, hardness, and plate shape, be optimized, but also residual stress can be significantly reduced, residual stress distribution can be improved, and the tubes can be made less prone to deformation and cracking during subsequent tube manufacturing.

[0230] Preferably, for the steel plate with a thickness d of 6~20mm, the tempering temperature T is B. s +(-65~55)℃.

[0231] For the steel plate with a thickness d of 20~50mm, the tempering temperature T is B. s +(-85~35)℃.

[0232] For the steel plate with a thickness d > 50 mm, the tempering temperature T is B. s +(-105~15)℃.

[0233] In this way, by coordinating the tempering temperature T and the tempering holding time t1, and further precisely controlling the tempering temperature T according to different thicknesses, it is possible to effectively reduce residual stress and avoid the decline in material properties, especially the superior strength and toughness. On the other hand, it is also possible to avoid the problem of excessive energy consumption and production costs caused by the introduction of tempering heat treatment.

[0234] Preferably, in this process, tempering heat treatment can be carried out in a tempering furnace, where a nitrogen atmosphere can be maintained.

[0235] Thus, under a nitrogen atmosphere, not only can oxidation or decarburization of the steel plate be prevented during tempering heat treatment, thus protecting the surface quality of the steel plate, research has also found that this can further optimize the uniformity of residual stress.

[0236] <Stacking process after tempering>

[0237] This process occurs after the tempering heat treatment process.

[0238] Specifically, after the tempering and holding time t1 is reached, the tempering is ended and the furnace is directly removed from the production line (i.e., removed from the tempering furnace) and stacked.

[0239] Among them, stacking temperature B s-(210~110)℃, cooling rate 10~30℃ / h, destacking temperature ≤B s -450℃.

[0240] Thus, by rapidly removing and stacking materials, and by controlling the cooling rate, the distribution of residual stress is made more uniform.

[0241] Preferably, the stacking time is 12~24h.

[0242] <Temperature Controlled Preheating and Straightening Process>

[0243] This process is located between the hot rolling process and the controlled water cooling process.

[0244] Specifically, the steel plate obtained from the hot rolling process is subjected to at least one pass of preheating and straightening.

[0245] The straightening speed is 0.1~1.5 m / s, and the straightening temperature is A. r3 +(3~77)℃, maximum reduction ≤4mm.

[0246] In this way, straightening the high-temperature steel plate after hot rolling and before controlled water cooling can significantly eliminate the flatness problems caused by hot rolling, such as warping, buckling, edge waviness, and center waviness, and ensure that the steel plate maintains high flatness before the controlled water cooling process. Moreover, straightening before the phase transformation in the controlled water cooling process can release some of the internal stress generated by rolling deformation, and ultimately reduce the residual stress of the finished steel plate.

[0247] Preferably, in this process, the straightening temperature is A. r3 +3℃, A r3 +5℃, A r3 +10℃, A r3 +15℃, A r3 +20℃, A r3 +25℃, A r3 +30℃, A r3 +35℃, A r3 +40℃, A r3 +45℃, A r3 +50℃, A r3 +55℃, A r3 +60℃, A r3 +65℃, A r3 +70℃, A r3 +75℃, A r3 Any value within +77℃.

[0248] <Temperature-controlled heat straightening process>

[0249] This process is located between the controlled water cooling process and the air-cooled self-tempering process.

[0250] Specifically, the steel plate after exiting the water cooling process is subjected to 1 to 3 passes of hot straightening.

[0251] The straightening speed is 0.1~1.5 m / s, and the straightening temperature is B. s +(-125~225)℃, maximum reduction ≤4mm.

[0252] Thus, the steel plate, after water cooling and before air cooling and self-tempering, is still in the ferrite or bainite phase transformation region. At this time, straightening can release the phase transformation stress and thermal stress, thereby ultimately reducing the residual stress of the finished steel plate.

[0253] Preferably, in this process, the straightening temperature is B. s -125℃, B s -120℃, B s -110℃, B s -80℃, B s -50℃, B s -40℃, B s -20℃, B s -10℃, B s B s +10℃, B s +20℃, B s +50℃, B s +90℃, B s +120℃, B s +150℃, B s +180℃, B s +210℃, B s Any value within +225℃.

[0254] <Temperature Control and Straightening Process>

[0255] This process is located between the air-cooled self-tempering process and the surface treatment process. In embodiments with a stacking process, this process is located between the air-cooling process and the stacking process.

[0256] Specifically, after the steel plate is removed from the cooling bed during the air-cooled self-tempering process, it undergoes 2 to 4 passes of temperature straightening.

[0257] The straightening speed is 0.1~0.5 m / s, and the straightening temperature is M. s -(270~150)℃, maximum reduction ≤10mm.

[0258] Thus, during the air-cooled self-tempering process, certain residual stress will still be generated, which may lead to warping. Straightening the steel plate after air-cooled self-tempering can further release phase transformation stress and thermal stress, thereby ultimately reducing the residual stress of the finished steel plate.

[0259] Preferably, in this process, the straightening temperature is M. s -270℃, M s -260℃, M s -250℃, M s -240℃, M s -230℃, M s -220℃, M s -210℃, M s -200℃, M s -190℃, M s -180℃, M s -170℃, M s -160℃, M s Any value within -150℃.

[0260] <Temperature-controlled cold straightening process>

[0261] This process is located between the air-cooled self-tempering process and the surface treatment process. In embodiments with a temperature-controlled straightening process, this process is located between the temperature-controlled straightening process and the surface treatment process. In embodiments with a stacking process, this process is located between the stacking process and the surface treatment process.

[0262] In this process, the steel plate undergoes 1 to 3 passes of cold straightening.

[0263] The straightening speed is 0.1~0.5 m / s, and the straightening temperature is M. s -(420~360)℃, maximum reduction ≤6mm.

[0264] This further releases phase transformation stress and thermal stress, ultimately reducing the residual stress in the finished steel plate.

[0265] Preferably, in this process, the straightening temperature is M. s -420℃, M s -410℃, M s -400℃, M s -390℃, M s -380℃, M s -370℃, M s Any value within -360℃.

[0266] The foregoing has described the technical principles and basic details of various embodiments of the present invention. Several embodiments are provided below to demonstrate the beneficial effects of this application. Of course, these embodiments are only a part of the numerous variations contained in this invention, and not all of them.

[0267] First Embodiment

[0268] This embodiment provides a steel plate for shipbuilding and marine engineering, and a method for producing the same. Specifically, the steel plate is a 235MPa grade or A / B / D / E grade steel plate for shipbuilding and marine engineering.

[0269] The chemical composition of the steel plate, by mass percentage, includes: C 0.07~0.11%, Si 0.19~0.31%, Mn 1.02~1.18%, Nb 0.009~0.021%, Ti 0.009~0.021%, Al 0.021~0.049%, P 0.0050~0.0180%, S 0.0005~0.0060%, O 0.0011~0.0025%, N 0.0022~0.0048%, H 0.00005~0.0002%, with the remainder being iron and unavoidable impurities.

[0270] Furthermore, the chemical composition of the steel plate, by mass percentage, also satisfies the following: CEV 0.240~0.307, Pcm 0.127~0.179, Ni / Cu 0.95~1.05, and 5C+Si+Mn+Cr+Ni+Mo+Cu 1.46~4.13.

[0271] Furthermore, the residual stress of the steel plate is ≤30MPa.

[0272] The steel plate exhibits small fluctuations and uniform distribution of residual stress throughout the plate. For example, the residual stress difference between any two locations at the head, middle, tail, upper, and lower parts is ≤10MPa.

[0273] In this embodiment, the thickness d of the steel plate is ≥ 6 mm. For example, the thickness d is 6~100 mm.

[0274] In this embodiment, the steel plate exhibits excellent mechanical properties:

[0275] R m The pressure is 400~520MPa;

[0276] R eH ≥235MPa;

[0277] A5≥22%;

[0278] R eH / R m ≤0.75;

[0279] Z-direction reduction of area ≥35%.

[0280] The steel plate has excellent toughness:

[0281] Impact energy at 20℃ KV2≥300J;

[0282] Impact energy at 0℃ KV2≥280J;

[0283] Impact energy at -20℃ KV2≥240J;

[0284] Impact energy at -40℃ KV2≥200J;

[0285] At 0℃, the crack tip opening displacement of CTOD is ≥0.5mm;

[0286] At -20℃, the crack tip opening displacement of CTOD is ≥0.3mm;

[0287] At -40℃, the crack tip opening displacement of CTOD is ≥0.2mm.

[0288] In addition, the steel plate has excellent shape, with an unevenness of ≤1mm / m.

[0289] Furthermore, the microstructure of the steel plate is polygonal ferrite + pearlite, and the total volume ratio of polygonal ferrite and pearlite is 100%.

[0290] Among them, polygonal ferrite accounts for 80-95% of the volume, and pearlite accounts for 5-20% of the volume.

[0291] The average grain size of the steel plate is 20~35μm.

[0292] Furthermore, the production method includes a sequential process of billet heating, hot rolling, optional temperature-controlled preheating and straightening, controlled water cooling, optional temperature-controlled hot straightening, air-cooled self-tempering, optional temperature-controlled hot straightening, optional stacking, optional temperature-controlled cold straightening, surface treatment, optional tempering heat treatment, and optional post-tempering stacking, to process the billet into the steel plate.

[0293] The following sections will describe each process in detail in order.

[0294] <Bill Heating Process>

[0295] The thickness of the cast billet is above 200mm, for example, 220~320mm.

[0296] The heat spreader temperature is T NbC +(50~125)℃, heat soaking time ≥25min.

[0297] Preferably, this process can employ segmented heating, such as including heat recovery, preheating, primary heating, secondary heating, and homogenization. However, it is not limited to this.

[0298] The heat recovery temperature is ≤800℃, the preheating temperature is ≤900℃, the first heating temperature is 970~1030℃, the second heating temperature is 1070~1130℃, and the total heating time is 0.019~0.023h / mm billet thickness.

[0299] Furthermore, the furnace entry temperature of the billet is ≥ M S -350℃.

[0300] <Hot Rolling Process>

[0301] In this process, the billet is rolled into a steel plate with a thickness d≥6mm through a first-stage rolling, intermediate billet cooling, and a second-stage rolling.

[0302] The thickness d of the steel plate is, for example, 6~100mm.

[0303] During the first stage of rolling, the initial rolling temperature T nr +(20~160)℃, final rolling temperature T nr +(-10~150)℃, the reduction in each pass is ≤26mm.

[0304] During the cooling of the intermediate billet, the thickness of the intermediate billet is 2.0 to 2.5 times the target thickness of the steel plate.

[0305] Furthermore, during the cooling of the intermediate billet, the intermediate billet is cooled to a final cooling temperature A. r3 +(130~150)℃, cooling time ≥50s.

[0306] Intermediate billets can be cooled by air cooling.

[0307] Next, during the second stage of rolling, the initial rolling temperature A r3 +(125~145)℃, final rolling temperature A r3 +(60~80)℃, hold for 8~10s before the last rolling pass.

[0308] Furthermore, during the second stage of rolling, the reduction in each pass is ≤20mm, and the reduction in the final pass is ≤3mm.

[0309] <Optional temperature-controlled preheating and straightening process>

[0310] In this embodiment, a temperature-controlled preheating and straightening process is preferably performed after the hot rolling process. Of course, the temperature-controlled preheating and straightening process can also be omitted.

[0311] Specifically, the steel plate obtained from the hot rolling process is subjected to at least one pass of preheating and straightening.

[0312] The straightening speed is 0.1~1.5 m / s, and the straightening temperature is A. r3 +(57~77)℃, maximum reduction ≤4mm.

[0313] <Controlled Water Cooling Process>

[0314] In this process, the rolled steel plate is cooled by water in an ultra-fast cooling system.

[0315] Inlet water temperature A r3 +(55~75)℃, outlet water temperature B s +(200~250)℃, cooling rate 3~18℃ / s.

[0316] The roller speed of the ultra-fast cooling system is preferably controlled at 0.5~1.5m / s.

[0317] Furthermore, in an optional implementation, the cooling manifold in the ultrafast cooling system can be controlled in an intermittent manner or in a head-and-tail shielding manner.

[0318] The intermittent method is specifically exemplified by the ultra-fast cooling system, which includes more than 24 sets of cooling manifolds distributed along the roller conveyor. Furthermore, the cooling manifolds are controlled in such a way that, along the roller conveyor, for every 1 to 2 sets of cooling manifolds that are turned on, there are 1 to 2 sets of cooling manifolds that are turned off at intervals.

[0319] The head and tail shielding method is specifically as follows: the steel plate is divided into Xn head low-temperature zones, a middle zone, and Xm tail low-temperature zones from head to tail, where Xn and Xm are positive integers greater than 1; using the cooling water volume Q per unit length in the middle zone as a standard, the cooling water volume per unit length in the Xn head low-temperature zones is controlled to increase sequentially from the head, and each is k times Q. X1 ~k Xn The K values ​​are: times, and the cooling water volume per unit length of the Xm tail-end low-temperature zones increases sequentially from the tail end, with each value being Q. X1 ~K Xm times; where k X1 ~k Xn All values ​​range from 0.55 to 0.85, K X1 ~K Xm The values ​​are all between 0.50 and 0.80.

[0320] For example, Xn and Xm can both be 3, and correspondingly, k X1 k X2 k X3 K takes values ​​of 0.55~0.65, 0.65~0.75, and 0.75~0.85 respectively. X1 K X2 K X3 The values ​​are 0.50~0.60, 0.60~0.70, and 0.70~0.80 respectively.

[0321] <Optional temperature-controlled thermal straightening process>

[0322] In this embodiment, a temperature-controlled hot straightening process is preferably performed after the water cooling process. Of course, the temperature-controlled hot straightening process can also be omitted.

[0323] Specifically, the steel plate after exiting the water cooling process is subjected to 1 to 3 passes of hot straightening.

[0324] The straightening speed is 0.1~1.5 m / s, and the straightening temperature is B. s +(180~220)℃, maximum reduction ≤4mm.

[0325] <Air-cooled self-tempering process>

[0326] In this process, the steel plate is cooled by air cooling on a cooling bed, during which self-tempering occurs.

[0327] upper cooling bed temperature B s +(150~200)℃.

[0328] Furthermore, in this process, the temperature of the lower cooling bed for the steel plate does not exceed M. s -150℃.

[0329] Preferably, the temperature of the lower cooling bed is M. s -(200~150)℃.

[0330] <Optional temperature-controlled straightening process>

[0331] In this embodiment, a temperature-controlled straightening process is preferably performed after the air-cooled self-tempering process. Of course, the temperature-controlled straightening process can also be omitted.

[0332] Specifically, after the steel plate is removed from the cooling bed during the air-cooled self-tempering process, it undergoes 2 to 4 passes of temperature straightening.

[0333] The straightening speed is 0.1~0.5 m / s, and the straightening temperature is M. s -(270~150)℃, maximum reduction ≤10mm.

[0334] <Optional stacking process>

[0335] In this embodiment, a stacking process can preferably be performed after the temperature-controlled straightening process, or the stacking process can be omitted.

[0336] In this process, the steel plate and the auxiliary steel plate are stacked together.

[0337] Specifically, the steel plate is sandwiched between two auxiliary steel plates and stacked in a layered manner of auxiliary steel plate-steel plate-auxiliary steel plate. That is, the lower surface of the steel plate is completely covered by the lower auxiliary steel plate, and the upper surface of the steel plate is completely covered by the upper auxiliary steel plate.

[0338] The stacking temperature M of the auxiliary steel plates used is... s +(-50~50)℃.

[0339] The stacking temperature of the steel plates is ≤ M. s -160℃, destacking temperature is M s -(340~240)℃.

[0340] The stacking time is preferably 12-18 hours.

[0341] <Optional temperature-controlled cold straightening process>

[0342] In this embodiment, a temperature-controlled cold straightening process can be preferably performed after the stacking process, or the temperature-controlled cold straightening process can be omitted.

[0343] In this process, the steel plate undergoes 1 to 3 passes of cold straightening.

[0344] The straightening speed is 0.1~0.5 m / s, and the straightening temperature is M. s -(420~360)℃, maximum reduction ≤6mm.

[0345] <Surface Treatment Process>

[0346] After the steel plate is cooled to room temperature, it is surface treated by shot blasting or shot peening.

[0347] During this period, one, two, or all of the following three conditions must be met:

[0348] Condition 1, t=k×d+C;

[0349] Condition 2, P = k1 × d + C1;

[0350] Condition 3: S = k2 × d + C2.

[0351] Where t is the duration of shot blasting or shot peening in min, k is 0.1~0.2 min / mm, C is 5~7 min, P is the shot blasting or shot peening rate in kg / min, k1 is 0.4~0.6 kg / (min·mm), C1 is 160~200 kg / min, S is the shot blasting or shot peening velocity in m / s, k2 is 0.1~0.3 m / (s·mm), C2 is 65~75 m / s;

[0352] Preferably, for the steel plate with a thickness d of 6~20mm, the shot used for shot blasting or shot peening is a mixture of shot with a diameter of 0.5mm and shot with a diameter of 0.7mm in a mass ratio of (7~8):5.

[0353] For the steel plate with a thickness d of 20~50mm, the shot used for shot blasting or shot peening is a mixture of shot with a diameter of 0.7mm and shot with a diameter of 1.0mm in a mass ratio of (9~11):5.

[0354] For the steel plate with a thickness d > 50 mm, the shot used for shot blasting or shot peening is a mixture of shot with a diameter of 1.0 mm and shot with a diameter of 1.2 mm in a mass ratio of (4~6):5.

[0355] Optionally, the shot used may be cast steel shot with a hardness of 35-50 HRC. The specific material of the cast steel shot is not limited in this application.

[0356] Furthermore, the shot blasting or shot peening angle is 45°~80°, with a coverage rate of 100%.

[0357] <Optional tempering heat treatment process>

[0358] This process occurs after the surface treatment process.

[0359] In this process, the heating rate is 8~15℃ / min, and the tempering temperature T is B. s +(-105~55)℃, and control the tempering holding time t1 according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥13.7, where t1 is in min.

[0360] Preferably, for the steel plate with a thickness d of 6~20mm, the tempering temperature T is B. s +(-65~55)℃.

[0361] For the steel plate with a thickness d of 20~50mm, the tempering temperature T is B. s +(-85~35)℃.

[0362] For the steel plate with a thickness d > 50 mm, the tempering temperature T is B. s +(-105~15)℃.

[0363] Preferably, in this process, tempering heat treatment can be carried out in a tempering furnace, where a nitrogen atmosphere can be maintained.

[0364] <Optional post-tempering stacking process>

[0365] This process occurs after the tempering heat treatment process.

[0366] Specifically, after the tempering and holding time t1 is reached, the tempering is ended and the furnace is directly removed from the production line (i.e., removed from the tempering furnace) and stacked.

[0367] Among them, stacking temperature B s-(210~110)℃, cooling rate 10~30℃ / h, destacking temperature ≤B s -450℃.

[0368] Preferably, the stacking time is 12~24h.

[0369] The following are some experimental examples of this embodiment.

[0370] First, Table 1 shows the chemical composition of the steel plates in several test examples.

[0371] [Table 1]

[0372]

[0373] Each test example was prepared using the specific production method of this first embodiment, and some parameters of each process are shown in Tables 2 to 4. " / " indicates that the corresponding process was not performed.

[0374] [Table 2]

[0375]

[0376] [Table 3]

[0377]

[0378] [Table 4]

[0379]

[0380] The microstructure and properties of the steel plates described in each test example were tested, and the results are shown in Tables 5 and 6. Additionally, Figure 1 The metallographic structure of Experimental Example 1 is shown.

[0381] [Table 5]

[0382]

[0383] [Table 6]

[0384]

[0385] Second Embodiment

[0386] This embodiment provides a steel plate for shipbuilding and marine engineering and a method for producing the same. Specifically, the steel plate is a 315MPa grade or AH32 / DH32 / EH32 / FH32 grade steel plate for shipbuilding and marine engineering.

[0387] The only differences between this embodiment and the first embodiment are in the chemical composition, some tissues and properties, and some process parameters. The following description focuses on these differences; other technical aspects are the same as in the first embodiment and can be found in the preceding description of the first embodiment, so they will not be repeated here.

[0388] In this embodiment, the chemical composition of the steel plate, by mass percentage, includes: C 0.06~0.10%, Si 0.20~0.32%, Mn 1.12~1.28%, Cr 0.06~0.24%, Nb 0.014~0.026%, Ti 0.009~0.021%, Al 0.021~0.049%, P 0.0050~0.0160%, S 0.0005~0.0050%, O 0.0011~0.0025%, N 0.0022~0.0048%, H 0.00005~0.0002%, with the remainder being iron and unavoidable impurities.

[0389] Furthermore, the chemical composition of the steel plate, by mass percentage, also satisfies the following: CEV 0.259~0.362, Pcm 0.126~0.187, Ni / Cu 0.95~1.05, and 5C+Si+Mn+Cr+Ni+Mo+Cu 1.46~4.13.

[0390] Furthermore, the residual stress of the steel plate is ≤40MPa.

[0391] The steel plate exhibits small fluctuations and uniform distribution of residual stress throughout the plate. For example, the residual stress difference between any two points at the head, middle, tail, upper, and lower parts is ≤15MPa.

[0392] In this embodiment, the thickness d of the steel plate is ≥ 6 mm. For example, the thickness d is 6~100 mm.

[0393] In this embodiment, the steel plate exhibits excellent mechanical properties:

[0394] R m The pressure is 450~570MPa;

[0395] R eH ≥315MPa;

[0396] A5≥22%;

[0397] R eH / R m ≤0.75;

[0398] Z-direction reduction of area ≥40%.

[0399] The steel plate has excellent toughness:

[0400] Impact energy at 0℃ KV2≥250J;

[0401] Impact energy at -20℃ KV2≥220J;

[0402] Impact energy at -40℃ KV2≥200J;

[0403] -60℃ impact energy KV2≥180J;

[0404] At 0℃, the crack tip opening displacement of CTOD is ≥0.6mm;

[0405] At -20℃, the crack tip opening displacement of CTOD is ≥0.4mm;

[0406] At -40℃, the crack tip opening displacement of CTOD is ≥0.3mm.

[0407] In addition, the steel plate has excellent shape, with an unevenness of ≤1mm / m.

[0408] Furthermore, the microstructure of the steel plate is polygonal ferrite + pearlite, and the total volume ratio of polygonal ferrite and pearlite is 100%.

[0409] Among them, polygonal ferrite accounts for 75-90% of the volume, and pearlite accounts for 10-25% of the volume.

[0410] The average grain size of the steel plate is 10~25μm.

[0411] In this embodiment, some parameters of the following processes differ from those in the first embodiment described above.

[0412] <Hot Rolling Process>

[0413] When the intermediate billet is cooled, the final cooling temperature A r3 +(100~120)℃, cooling time ≥80s.

[0414] During the second stage of rolling, the initial rolling temperature A r3 +(95~115)℃, final rolling temperature A r3 +(50~70)℃.

[0415] <Controlled Water Cooling Process>

[0416] Inlet water temperature A r3 +(45~65)℃, outlet water temperature B s +(150~180)℃.

[0417] <Air-cooled self-tempering process>

[0418] upper cooling bed temperature B s +(100~130)℃.

[0419] The temperature of the steel plate on the lower cooling bed shall not exceed M. s -160℃. Preferably, the temperature of the lower cooling bed is M. s -(210~160)℃.

[0420] <Optional stacking process>

[0421] In this embodiment, a stacking process can preferably be performed after the temperature-controlled straightening process, or the stacking process can be omitted.

[0422] In this process, the steel plate and the auxiliary steel plate are stacked together.

[0423] The stacking temperature M of the auxiliary steel plates used is... s +(-60~40)℃.

[0424] The stacking temperature of the steel plates is ≤ M. s -160℃, destacking temperature is M s -(350~250)℃.

[0425] The following are some experimental examples of this embodiment.

[0426] First, Table 7 shows the chemical composition of the steel plates in several test examples.

[0427] [Table 7]

[0428]

[0429] Each test case was prepared using the specific production method of this embodiment, and some parameters of each process are shown in Tables 8 to 10. " / " indicates that the corresponding process was not performed.

[0430] [Table 8]

[0431]

[0432] [Table 9]

[0433]

[0434] [Table 10]

[0435]

[0436] The microstructure and properties of the steel plates described in each test example were tested, and the results are shown in Tables 11 and 12. Additionally, Figure 2 The metallographic structure of Experimental Example 1A is shown.

[0437] [Table 11]

[0438]

[0439] [Table 12]

[0440]

[0441] Third Embodiment

[0442] This embodiment provides a steel plate for shipbuilding and marine engineering, and a method for producing the same. Specifically, the steel plate is a 355MPa grade or AH36 / DH36 / EH36 / FH36 grade steel plate for shipbuilding and marine engineering.

[0443] The only differences between this embodiment and the first embodiment are in the chemical composition, some tissues and properties, and some process parameters. The following description focuses on these differences; other technical aspects are the same as in the first embodiment and can be found in the preceding description of the first embodiment, so they will not be repeated here.

[0444] In this embodiment, the chemical composition of the steel plate, by mass percentage, includes: C 0.06~0.10%, Si 0.14~0.26%, Mn 1.27~1.43%, Cr 0.06~0.24%, Ni 0.06~0.24%, Cu 0.06~0.24%, Nb 0.024~0.036%, Ti 0.009~0.021%, Al 0.021~0.049%, P 0.0050~0.0140%, S 0.0005~0.0040%, O 0.0011~0.0025%, N 0.0022~0.0048%, H 0.00005~0.0002%, with the remainder being iron and unavoidable impurities.

[0445] Furthermore, the chemical composition of the steel plate, by mass percentage, also satisfies the following: CEV is 0.292~0.418, Pcm is 0.135~0.208, Ni / Cu is 0.95~1.05, and 5C+Si+Mn+Cr+Ni+Mo+Cu is 1.46~4.13.

[0446] Furthermore, the residual stress of the steel plate is ≤40MPa.

[0447] The steel plate exhibits small fluctuations and uniform distribution of residual stress throughout the plate. For example, the residual stress difference between any two points at the head, middle, tail, upper, and lower parts is ≤15MPa.

[0448] In this embodiment, the thickness d of the steel plate is ≥ 6 mm. For example, the thickness d is 6~100 mm.

[0449] In this embodiment, the steel plate exhibits excellent mechanical properties:

[0450] R m The pressure ranges from 490 to 630 MPa.

[0451] R eH ≥355MPa;

[0452] A5≥21%;

[0453] R eH / R m ≤0.80;

[0454] Z-direction reduction of area ≥40%.

[0455] The steel plate has excellent toughness:

[0456] Impact energy at 0℃ KV2≥260J;

[0457] Impact energy at -20℃ KV2≥240J;

[0458] Impact energy at -40℃ KV2≥220J;

[0459] Impact energy at -60℃ KV2≥200J;

[0460] At 0℃, the crack tip opening displacement of CTOD is ≥0.6mm;

[0461] At -20℃, the crack tip opening displacement of CTOD is ≥0.4mm;

[0462] At -40℃, the crack tip opening displacement of CTOD is ≥0.3mm.

[0463] In addition, the steel plate has excellent shape, with an unevenness of ≤1mm / m.

[0464] Furthermore, the microstructure of the steel plate is polygonal ferrite + pearlite, and the total volume ratio of polygonal ferrite and pearlite is 100%.

[0465] Among them, polygonal ferrite accounts for 70-85% of the volume, and pearlite accounts for 15-30% of the volume.

[0466] The average grain size of the steel plate is 8~22μm.

[0467] In this embodiment, some parameters of the following processes differ from those in the first embodiment described above.

[0468] <Hot Rolling Process>

[0469] When the intermediate billet is cooled, the final cooling temperature A r3 +(90~110)℃, cooling time ≥90s.

[0470] During the second stage of rolling, the initial rolling temperature A r3 +(85~105)℃, final rolling temperature A r3+(40~60)℃.

[0471] <Controlled Water Cooling Process>

[0472] Inlet water temperature A r3 +(35~55)℃, outlet water temperature B s +(110~140)℃.

[0473] <Air-cooled self-tempering process>

[0474] upper cooling bed temperature B s +(60~90)℃.

[0475] The temperature of the steel plate on the lower cooling bed shall not exceed M. s -170℃. Preferably, the temperature of the lower cooling bed is M. s -(220~170)℃.

[0476] <Optional stacking process>

[0477] In this embodiment, a stacking process can preferably be performed after the temperature-controlled straightening process, or the stacking process can be omitted.

[0478] In this process, the steel plate and the auxiliary steel plate are stacked together.

[0479] The stacking temperature M of the auxiliary steel plates used is... s +(-70~30)℃.

[0480] The stacking temperature of the steel plates is ≤ M. s -170℃, destacking temperature is M s -(360~260)℃.

[0481] The following are some experimental examples of this embodiment.

[0482] First, Table 13 shows the chemical composition of the steel plates in several test examples.

[0483] [Table 13]

[0484]

[0485] Each test case was prepared using the specific production method of this embodiment, and some parameters of each process are shown in Tables 14 to 16. " / " indicates that the corresponding process was not performed.

[0486] [Table 14]

[0487]

[0488] [Table 15]

[0489]

[0490] [Table 16]

[0491]

[0492] The microstructure and properties of the steel plates described in each test example were tested, and the results are shown in Tables 17 and 18. Additionally, Figure 3 The metallographic structure of Experimental Example 1B is shown.

[0493] [Table 17]

[0494]

[0495] [Table 18]

[0496]

[0497] Fourth embodiment

[0498] This embodiment provides a steel plate for shipbuilding and marine engineering and a method for producing the same. Specifically, the steel plate is a 390MPa grade or AH40 / DH40 / EH40 / FH40 grade steel plate for shipbuilding and marine engineering.

[0499] The only differences between this embodiment and the first embodiment are in the chemical composition, some tissues and properties, and some process parameters. The following description focuses on these differences; other technical aspects are the same as in the first embodiment and can be found in the preceding description of the first embodiment, so they will not be repeated here.

[0500] In this embodiment, the chemical composition of the steel plate, by mass percentage, includes: C 0.06~0.10%, Si 0.14~0.26%, Mn 1.37~1.53%, Cr 0.06~0.24%, Ni 0.16~0.34%, Cu 0.16~0.34%, Nb 0.034~0.046%, Ti 0.009~0.021%, Al 0.021~0.049%, P 0.0050~0.0140%, S 0.0005~0.0040%, O 0.0011~0.0025%, N 0.0022~0.0048%, H 0.00005~0.0002%, with the remainder being iron and unavoidable impurities.

[0501] Furthermore, the chemical composition of the steel plate, by mass percentage, also satisfies the following: CEV 0.322~0.448, Pcm 0.147~0.220, Ni / Cu 0.95~1.05, and 5C+Si+Mn+Cr+Ni+Mo+Cu 1.46~4.13.

[0502] Furthermore, the residual stress of the steel plate is ≤40MPa.

[0503] The steel plate exhibits small fluctuations and uniform distribution of residual stress throughout the plate. For example, the residual stress difference between any two points at the head, middle, tail, upper, and lower parts is ≤15MPa.

[0504] In this embodiment, the thickness d of the steel plate is ≥ 6 mm. For example, the thickness d is 6~100 mm.

[0505] In this embodiment, the steel plate exhibits excellent mechanical properties:

[0506] R m The pressure is 510~660MPa;

[0507] R eH ≥390MPa;

[0508] A5≥20%;

[0509] R eH / R m ≤0.80;

[0510] Z-direction reduction of area ≥40%.

[0511] The steel plate has excellent toughness:

[0512] Impact energy at 0℃ KV2≥270J;

[0513] Impact energy at -20℃ KV2≥260J;

[0514] Impact energy at -40℃ KV2≥240J;

[0515] Impact energy at -60℃ KV2≥220J;

[0516] At 0℃, the crack tip opening displacement of CTOD is ≥0.6mm;

[0517] At -20℃, the crack tip opening displacement of CTOD is ≥0.4mm;

[0518] At -40℃, the crack tip opening displacement of CTOD is ≥0.3mm.

[0519] In addition, the steel plate has excellent shape, with an unevenness of ≤1mm / m.

[0520] Furthermore, the microstructure of the steel plate is polygonal ferrite + pearlite + tempered bainite, and the total volume percentage of polygonal ferrite, pearlite and tempered bainite is 100%.

[0521] Among them, polygonal ferrite accounts for 65-80% of the volume, pearlite accounts for 20-30% of the volume, and tempered bainite accounts for 0-5% of the volume.

[0522] The average grain size of the steel plate is 7~18μm.

[0523] In this embodiment, some parameters of the following processes differ from those in the first embodiment described above.

[0524] <Hot Rolling Process>

[0525] When the intermediate billet is cooled, the final cooling temperature A r3 +80~100℃, cooling time ≥100s.

[0526] During the second stage of rolling, the initial rolling temperature A r3 +(75~95)℃, final rolling temperature A r3 +(30~50)℃.

[0527] <Controlled Water Cooling Process>

[0528] Inlet water temperature A r3 +(25~45)℃, outlet water temperature B s +(60~90)℃.

[0529] <Air-cooled self-tempering process>

[0530] upper cooling bed temperature B s +(10~40)℃.

[0531] The temperature of the steel plate on the lower cooling bed shall not exceed M. s -180℃. Preferably, the temperature of the lower cooling bed is M. s -(230~180)℃.

[0532] <Optional stacking process>

[0533] In this embodiment, a stacking process can preferably be performed after the temperature-controlled straightening process, or the stacking process can be omitted.

[0534] In this process, the steel plate and the auxiliary steel plate are stacked together.

[0535] The stacking temperature M of the auxiliary steel plates used is... s +(-80~20)℃.

[0536] The stacking temperature of the steel plates is ≤ M. s -180℃, destacking temperature is M s -(370~270)℃.

[0537] The following are some experimental examples of this embodiment.

[0538] First, Table 19 shows the chemical composition of the steel plates in several test examples.

[0539] [Table 19]

[0540]

[0541] Each test case was prepared using the specific production method of this embodiment, and some parameters of each process are shown in Tables 20 to 22. " / " indicates that the corresponding process was not performed.

[0542] [Table 20]

[0543]

[0544] [Table 21]

[0545]

[0546] [Table 22]

[0547]

[0548] The microstructure and properties of the steel plates described in each test example were tested, and the results are shown in Tables 23 and 24. Additionally, Figure 4 The metallographic structure of Experimental Example 1C is shown.

[0549] [Table 23]

[0550]

[0551] [Table 24]

[0552]

[0553] Fifth Embodiment

[0554] This embodiment provides a steel plate for shipbuilding and marine engineering and a method for producing the same. Specifically, the steel plate is a 420MPa grade or AH420 / DH420 / EH420 / FH420 grade steel plate for shipbuilding and marine engineering.

[0555] The only differences between this embodiment and the first embodiment are in the chemical composition, some tissues and properties, and some process parameters. The following description focuses on these differences; other technical aspects are the same as in the first embodiment and can be found in the preceding description of the first embodiment, so they will not be repeated here.

[0556] In this embodiment, the chemical composition of the steel plate, by mass percentage, includes: C 0.05~0.09%, Si 0.09~0.21%, Mn 1.37~1.53%, Cr 0.06~0.24%, Ni 0.21~0.39%, Mo 0.02~0.14%, Cu 0.21~0.39%, Nb 0.039~0.051%, Ti 0.009~0.021%, Al 0.021~0.049%, P 0.0050~0.0120%, S 0.0005~0.0030%, O 0.0011~0.0025%, N 0.0022~0.0048%, H 0.00005~0.0002%, with the remainder being iron and unavoidable impurities.

[0557] Furthermore, the chemical composition of the steel plate, by mass percentage, also satisfies the following: CEV is 0.318~0.445, Pcm is 0.139~0.212, Ni / Cu is 0.95~1.05, and 5C+Si+Mn+Cr+Ni+Mo+Cu is 1.46~4.13.

[0558] Furthermore, the residual stress of the steel plate is ≤60MPa.

[0559] The steel plate exhibits small fluctuations and uniform distribution of residual stress throughout the plate. For example, the residual stress difference between any two locations at the head, middle, tail, upper, and lower parts is ≤20MPa.

[0560] In this embodiment, the thickness d of the steel plate is ≥ 6 mm. For example, the thickness d is 6~100 mm.

[0561] In this embodiment, the steel plate exhibits excellent mechanical properties:

[0562] R m The pressure is 520~680MPa;

[0563] R eH ≥420MPa;

[0564] A5≥19%;

[0565] R eH / R m ≤0.88;

[0566] Z-direction reduction of area ≥45%.

[0567] The steel plate has excellent toughness:

[0568] Impact energy at 0℃ KV2≥330J;

[0569] Impact energy at -20℃ KV2≥320J;

[0570] -40℃ impact energy KV2≥300J;

[0571] -60℃ impact energy KV2≥280J;

[0572] At 0℃, the crack tip opening displacement of CTOD is ≥1.0mm;

[0573] At -20℃, the crack tip opening displacement of CTOD is ≥0.8mm;

[0574] At -40℃, the crack tip opening displacement of CTOD is ≥0.5mm.

[0575] In addition, the steel plate has excellent shape, with an unevenness of ≤2mm / m.

[0576] Furthermore, the microstructure of the steel plate is polygonal ferrite + pearlite + tempered bainite, and the total volume percentage of polygonal ferrite, pearlite and tempered bainite is 100%.

[0577] Among them, polygonal ferrite accounts for 15-35% of the volume, pearlite accounts for 5-10% of the volume, and tempered bainite accounts for 60-75% of the volume.

[0578] The average grain size of the steel plate is 6~15μm.

[0579] In this embodiment, some parameters of the following processes differ from those in the first embodiment described above.

[0580] <Hot Rolling Process>

[0581] When the intermediate billet is cooled, the final cooling temperature A r3 +(70~90)℃, cooling time ≥110s.

[0582] During the second stage of rolling, the initial rolling temperature A r3 +(65~85)℃, final rolling temperature A r3 +(20~40)℃.

[0583] <Controlled Water Cooling Process>

[0584] Inlet water temperature A r3 +(15~35)℃, outlet water temperature B s +(-5~25)℃.

[0585] <Air-cooled self-tempering process>

[0586] upper cooling bed temperature B s -(55~25)℃.

[0587] The temperature of the steel plate on the lower cooling bed shall not exceed M. s -190℃. Preferably, the temperature of the lower cooling bed is M.s -(240~190)℃.

[0588] <Optional stacking process>

[0589] In this embodiment, a stacking process can preferably be performed after the temperature-controlled straightening process, or the stacking process can be omitted.

[0590] In this process, the steel plate and the auxiliary steel plate are stacked together.

[0591] The stacking temperature M of the auxiliary steel plates used is... s +(-90~10)℃.

[0592] The stacking temperature of the steel plates is ≤ M. s -190℃, destacking temperature is M s -(380~280)℃.

[0593] The following are some experimental examples of this embodiment.

[0594] First, Table 25 shows the chemical composition of the steel plates in several test examples.

[0595] [Table 25]

[0596]

[0597] Each test case was prepared using the specific production method of this embodiment, and some parameters of each process are shown in Tables 26 to 28. " / " indicates that the corresponding process was not performed.

[0598] [Table 26]

[0599]

[0600] [Table 27]

[0601]

[0602] [Table 28]

[0603]

[0604] The microstructure and properties of the steel plates described in each test example were tested, and the results are shown in Tables 29 and 30. Additionally, Figure 5 The metallographic structure of Experimental Example 1D is shown.

[0605] [Table 29]

[0606]

[0607] [Table 30]

[0608]

[0609] Sixth Embodiment

[0610] This embodiment provides a steel plate for shipbuilding and marine engineering and a method for producing the same. Specifically, the steel plate is a 460MPa grade or AH460 / DH460 / EH460 / FH460 grade steel plate for shipbuilding and marine engineering.

[0611] The only differences between this embodiment and the first embodiment are in the chemical composition, some tissues and properties, and some process parameters. The following description focuses on these differences; other technical aspects are the same as in the first embodiment and can be found in the preceding description of the first embodiment, so they will not be repeated here.

[0612] In this embodiment, the chemical composition of the steel plate, by mass percentage, includes: C 0.05~0.09%, Si 0.09~0.21%, Mn 1.47~1.63%, Cr 0.16~0.34%, Ni 0.16~0.34%, Mo 0.09~0.21%, Cu 0.16~0.34%, Nb 0.039~0.051%, Ti 0.009~0.021%, Al 0.021~0.049%, P 0.0050~0.0100%, S 0.0005~0.0020%, O 0.0011~0.0025%, N 0.0022~0.0048%, H 0.00005~0.0002%, with the remainder being iron and unavoidable impurities.

[0613] Furthermore, the chemical composition of the steel plate, by mass percentage, also satisfies the following: CEV 0.352~0.503, Pcm 0.147~0.228, Ni / Cu 0.95~1.05, and 5C+Si+Mn+Cr+Ni+Mo+Cu 1.46~4.13.

[0614] Furthermore, the residual stress of the steel plate is ≤70MPa.

[0615] The steel plate exhibits small fluctuations and uniform distribution of residual stress throughout the plate. For example, the residual stress difference between any two points at the head, middle, tail, upper, and lower sections is ≤25MPa.

[0616] In this embodiment, the thickness d of the steel plate is ≥ 6 mm. For example, the thickness d is 6~100 mm.

[0617] In this embodiment, the steel plate exhibits excellent mechanical properties:

[0618] R m The pressure is 540~720MPa;

[0619] R eH ≥460MPa;

[0620] A5≥17%;

[0621] R eH / R m ≤0.88;

[0622] Z-direction reduction of area ≥45%.

[0623] The steel plate has excellent toughness:

[0624] Impact energy at 0℃ KV2≥320J;

[0625] Impact energy at -20℃ KV2≥300J;

[0626] -40℃ impact energy KV2≥280J;

[0627] -60℃ impact energy KV2≥260J;

[0628] At 0℃, the crack tip opening displacement of CTOD is ≥1.0mm;

[0629] At -20℃, the crack tip opening displacement of CTOD is ≥0.8mm;

[0630] At -40℃, the crack tip opening displacement of CTOD is ≥0.5mm.

[0631] In addition, the steel plate has excellent shape, with an unevenness of ≤2mm / m.

[0632] Furthermore, the microstructure of the steel plate is polygonal ferrite + pearlite + tempered bainite, and the total volume percentage of polygonal ferrite, pearlite and tempered bainite is 100%.

[0633] Among them, polygonal ferrite accounts for 10-20% of the volume, pearlite accounts for 0-5% of the volume, and tempered bainite accounts for 75-90% of the volume.

[0634] The average grain size of the steel plate is 5~14μm.

[0635] In this embodiment, some parameters of the following processes differ from those in the first embodiment described above.

[0636] <Hot Rolling Process>

[0637] When the intermediate billet is cooled, the final cooling temperature A r3 +(60~80)℃, cooling time ≥120s.

[0638] During the second stage of rolling, the initial rolling temperature A r3 +(55~75)℃, final rolling temperature Ar3 +(10~30)℃.

[0639] <Controlled Water Cooling Process>

[0640] Inlet water temperature A r3 +(5~25)℃, outlet water temperature B s -(40~10)℃.

[0641] <Air-cooled self-tempering process>

[0642] upper cooling bed temperature B s -(90~60)℃.

[0643] The temperature of the steel plate on the lower cooling bed shall not exceed M. s -200℃. Preferably, the temperature of the lower cooling bed is M. s -(250~200)℃.

[0644] <Optional stacking process>

[0645] In this embodiment, a stacking process can preferably be performed after the temperature-controlled straightening process, or the stacking process can be omitted.

[0646] In this process, the steel plate and the auxiliary steel plate are stacked together.

[0647] The stacking temperature M of the auxiliary steel plates used is... s -(100~0)℃.

[0648] The stacking temperature of the steel plates is ≤ M. s -200℃, destacking temperature is M s -(390~280)℃.

[0649] The following are some experimental examples of this embodiment.

[0650] First, Table 31 shows the chemical composition of the steel plates in several test examples.

[0651] [Table 31]

[0652]

[0653] Each test case was prepared using the specific production method of this embodiment, and some parameters of each process are shown in Tables 32 to 34. " / " indicates that the corresponding process was not performed.

[0654] [Table 32]

[0655]

[0656] [Table 33]

[0657]

[0658] [Table 34]

[0659]

[0660] The microstructure and properties of the steel plates described in each test example were tested, and the results are shown in Tables 35 and 36. Additionally, Figure 6 The metallographic structure of Experimental Example 1E is shown.

[0661] [Table 35]

[0662]

[0663] [Table 36]

[0664]

[0665] Seventh Embodiment

[0666] This embodiment provides a steel plate for shipbuilding and marine engineering and a method for producing the same. Specifically, the steel plate is a 500MPa grade or AH500 / DH500 / EH500 / FH500 grade steel plate for shipbuilding and marine engineering.

[0667] The only differences between this embodiment and the first embodiment are in the chemical composition, some tissues and properties, and some process parameters. The following description focuses on these differences; other technical aspects are the same as in the first embodiment and can be found in the preceding description of the first embodiment, so they will not be repeated here.

[0668] In this embodiment, the chemical composition of the steel plate, by mass percentage, includes: C 0.05~0.09%, Si 0.09~0.21%, Mn 0.92~1.08%, Cr 0.36~0.54%, Ni 0.21~0.39%, Mo 0.19~0.31%, Cu 0.21~0.39%, Nb 0.044~0.056%, Ti 0.009~0.021%, Al 0.021~0.049%, P 0.0050~0.0100%, S 0.0005~0.0020%, O 0.0011~0.0025%, N 0.0022~0.0048%, H 0.00005~0.0002%, with the remainder being iron and unavoidable impurities.

[0669] Furthermore, the chemical composition of the steel plate, by mass percentage, also satisfies the following: CEV is 0.341~0.492, Pcm is 0.144~0.225, Ni / Cu is 0.95~1.05, and 5C+Si+Mn+Cr+Ni+Mo+Cu is 1.46~4.13.

[0670] Furthermore, the residual stress of the steel plate is ≤80MPa.

[0671] The steel plate exhibits small fluctuations and uniform distribution of residual stress throughout the plate. For example, the residual stress difference between any two locations at the head, middle, tail, upper, and lower parts is ≤30MPa.

[0672] In this embodiment, the thickness d of the steel plate is ≥ 6 mm. For example, the thickness d is 6~100 mm.

[0673] In this embodiment, the steel plate exhibits excellent mechanical properties:

[0674] R m The pressure is 590~770MPa;

[0675] R eH ≥500MPa;

[0676] A5≥17%;

[0677] R eH / R m ≤0.88;

[0678] Z-direction reduction of area ≥45%.

[0679] The steel plate has excellent toughness:

[0680] Impact energy at 0℃ KV2≥300J;

[0681] Impact energy at -20℃ KV2≥280J;

[0682] -40℃ impact energy KV2≥260J;

[0683] Impact energy at -60℃ KV2≥240J;

[0684] At 0℃, the crack tip opening displacement of CTOD is ≥1.0mm;

[0685] At -20℃, the crack tip opening displacement of CTOD is ≥0.8mm;

[0686] At -40℃, the crack tip opening displacement of CTOD is ≥0.5mm.

[0687] In addition, the steel plate has excellent shape, with an unevenness of ≤3mm / m.

[0688] Furthermore, the microstructure of the steel plate is polygonal ferrite + pearlite + tempered bainite, and the total volume percentage of polygonal ferrite, pearlite and tempered bainite is 100%.

[0689] Among them, polygonal ferrite accounts for 5-15% of the volume, pearlite accounts for 0-2% of the volume, and tempered bainite accounts for 85-93% of the volume.

[0690] The average grain size of the steel plate is 4~12μm.

[0691] In this embodiment, some parameters of the following processes differ from those in the first embodiment described above.

[0692] <Hot Rolling Process>

[0693] When the intermediate billet is cooled, the final cooling temperature A r3 +(50~70)℃, cooling time ≥130s.

[0694] During the second stage of rolling, the initial rolling temperature A r3 +(45~65)℃, final rolling temperature A r3 +(5~20)℃.

[0695] <Controlled Water Cooling Process>

[0696] Inlet water temperature A r3 +(0~15)℃, outlet water temperature B s -(100~70)℃.

[0697] <Air-cooled self-tempering process>

[0698] upper cooling bed temperature B s -(150~120)℃.

[0699] The temperature of the steel plate on the lower cooling bed shall not exceed M. s -210℃. Preferably, the temperature of the lower cooling bed is M. s -(260~210)℃.

[0700] <Optional stacking process>

[0701] In this embodiment, a stacking process can preferably be performed after the temperature-controlled straightening process, or the stacking process can be omitted.

[0702] In this process, the steel plate and the auxiliary steel plate are stacked together.

[0703] The stacking temperature M of the auxiliary steel plates used is... s -(110~10)℃.

[0704] The stacking temperature of the steel plates is ≤ M. s -210℃, destacking temperature is M s -(400~300)℃.

[0705] The following are some experimental examples of this embodiment.

[0706] First, Table 37 shows the chemical composition of the steel plates in several test examples.

[0707] [Table 37]

[0708]

[0709] Each test case was prepared using the specific production method of this embodiment, and some parameters of each process are shown in Tables 38 to 40. " / " indicates that the corresponding process was not performed.

[0710] [Table 38]

[0711]

[0712] [Table 39]

[0713]

[0714] [Table 40]

[0715]

[0716] The microstructure and properties of the steel plates described in each test example were tested, and the results are shown in Tables 41 and 42. Additionally, Figure 7 The metallographic structure of Experimental Example 1F is shown.

[0717] [Table 41]

[0718]

[0719] [Table 42]

[0720]

Claims

1. A method of producing a steel plate for ships and ocean engineering, characterized by, The chemical composition of the steel plate includes, in mass percent, C 0.05-0.11%, Si 0.09-0.32%, Mn 0.92-1.63%, Cr 0-0.54%, Ni 0-0.39%, Mo 0-0.31%, Cu 0-0.39%, Nb 0.009-0.056%, Ti 0.009-0.021%, Al 0.021-0.049%, P≤0.0180%, S≤0.0060%, O≤0.0025%, N≤0.0048%, H≤0.0002%, and the balance being iron and inevitable impurities; The production method comprises sequentially, The slab heating process: soaking temperature is T NbC +(50~125)℃, soaking time is ≥25min; Hot rolling process: having first stage rolling, intermediate product cooling and second stage rolling to obtain a steel plate with thickness d≥6 mm; in the first stage rolling, the starting rolling temperature T nr +(20~160)℃, the finishing rolling temperature T nr +(-10~150)℃, the reduction of each pass ≤26 mm; in the intermediate product cooling, the intermediate product thickness is 2.0~2.5 times of the target thickness of the steel plate, the final cooling temperature A r3 +(50~150)℃, the cooling time ≥50 s; in the second stage rolling, the starting rolling temperature A r3 +(45~145)℃, the finishing rolling temperature A r3 +(5~80)℃, the 8~10 s staying before the final pass rolling; Controlled water cooling process: water inlet temperature A r3 + (0~75)℃, water outlet temperature B s +(-100~250)℃, cooling speed 3~18℃ / s; an air cooling self-tempering process: air cooling on a cooling bed; a surface treatment process: after the steel plate is cooled to room temperature, surface treatment is performed on the steel plate by means of shot blasting or grit blasting; during the surface treatment, one, two or all of the following three conditions are met: t=k×d+C, P=k1×d+C1, S=k2×d+C2; wherein t is the time length of shot blasting or grit blasting, in min, k is 0.1-0.2 min / mm, C is 5-7 min, P is the shot blasting or grit blasting amount, in kg / min, k1 is 0.4-0.6 kg / (min·mm), C1 is 160-200 kg / min, S is the speed of shot blasting or grit blasting, in m / s, k2 is 0.1-0.3 m / (s·mm), and C2 is 65-75 m / s; wherein T NbC , T nr , A r3 , B s are calculated using the following equations, respectively, and the element symbols in each equation represent the mass percentage of the corresponding element in the slab. T NbC = 7700 / (3.18-lg(Nb x C 0.87 ))-273.15; T nr = 887 + 464C - 357Si + 6445Nb - 644 + 890Ti + 363Al; A r3 =910-203 -11Si-15.2Mn-30Cr-13Ni-40Mo; B s = 550 - 160 C - 10 Mn - 10 Cr - 10 Ni - 5 Mo.

2. The method of producing a steel plate for shipbuilding and offshore engineering according to claim 1, characterized in that, The production method further comprises a tempering heat treatment process after the surface treatment process: a temperature rising rate of 8-15 ℃ / min, a tempering temperature T of B s +(-105~55)℃, and the tempering holding time t1 is controlled according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥13.7, and the unit of t1 is min.

3. The production method of the steel plate for shipbuilding and ocean engineering according to claim 2, characterized in that, The thickness d of the steel plate is 6-20 mm, and the tempering temperature T is B s +(-65~55)℃; Alternatively, the thickness d of the steel sheet is 20 to 50 mm, and the tempering temperature T is B s +(-85 to 35) °C; Alternatively, the thickness d of the steel sheet is greater than 50 mm and the tempering temperature T is B s +(-105~15)℃.

4. The method of producing a steel plate for shipbuilding and offshore engineering according to claim 2, characterized in that, The production method further comprises a post-tempering stacking process after the tempering heat treatment process: after a tempering holding time t1 is reached, the tempering is ended and stacking is directly performed, the stacking temperature B s - (210-110) °C, cooling rate 10-30 °C / h, unstacking temperature ≤ B s - 450 °C.

5. The method of producing a steel plate for shipbuilding and offshore engineering according to claim 1, characterized in that, the thickness d of the steel plate is 6-20 mm, and the shot blasting or grit blasting uses mixed shot formed by shot with a diameter of 0.5 mm and shot with a diameter of 0.7 mm in a mass ratio of (7-8):5; alternatively, the thickness d of the steel plate is 20-50 mm, and the shot blasting or grit blasting uses mixed shot formed by shot with a diameter of 0.7 mm and shot with a diameter of 1.0 mm in a mass ratio of (9-11):5; alternatively, the thickness d of the steel plate is >50 mm, and the shot blasting or grit blasting uses mixed shot formed by shot with a diameter of 1.0 mm and shot with a diameter of 1.2 mm in a mass ratio of (4-6):

5.

6. The method of producing a steel plate for shipbuilding and offshore engineering according to claim 1, characterized in that, The production method further includes a stacking process between the air-cooling self-tempering process and the surface treatment process: the steel plate is clamped between two auxiliary steel plates to be stacked in the form of auxiliary steel plate-steel plate-auxiliary steel plate, the stacking temperature of the auxiliary steel plates is M s + (-110 ~ 50) °C, the stacking temperature of the steel plate is M s - (270 ~ 160) °C, the unstacking temperature is not more than M s - (400 ~ 240) °C; wherein M S The following formula is used to calculate the temperature in °C, with the element symbols representing the mass percentage of the corresponding element in the strand. M S = 539 - 423 C - 11 Si - 30.4 Mn - 12.1 Cr - 17.7 Ni - 7.5 Mo.

7. The method of producing a steel plate for shipbuilding and offshore engineering according to claim 1, characterized in that, Air cooling and self tempering process: upper cooling bed temperature B s +(-150~200)℃, lower cooling bed temperature M s -(260~150)℃; wherein M S The following formula is used to calculate the temperature, in °C, where the element symbols represent the mass percentage of the corresponding element in the strand. M S = 539 - 423 C - 11 Si - 30.4 Mn - 12.1 Cr - 17.7 Ni - 7.5 Mo.

8. The method of producing a steel plate for shipbuilding and offshore engineering according to claim 1, characterized in that, During the second-stage rolling, the reduction of each pass is ≤20 mm, and the reduction of the last pass is ≤3 mm.

9. The method of producing a steel plate for shipbuilding and offshore engineering according to claim 1, characterized in that, The production method further comprises one, two, three or all of the following four processes, In the temperature-controlled preheating and straightening process between the hot rolling process and the controlled water cooling process: at least one preheating and straightening pass is performed, with a straightening speed of 0.1~1.5 m / s and a straightening temperature A. r3 +(3~77)℃, maximum reduction ≤4mm; In the temperature control heat straightening process between the water cooling process and the air cooling self-tempering process: 1-3 passes of heat straightening is carried out, the straightening speed is 0.1-1.5 m / s, and the straightening temperature B is 650-750°C s +(-125~225)℃, maximum reduction ≤4mm; In the temperature-controlled straightening process between the air-cooling self-tempering process and the surface treatment process: 2-4 passes of temperature straightening, straightening speed 0.1-0.5 m / s, straightening temperature M s - (270-150) °C, maximum reduction ≤ 10 mm; Temperature-controlled cold straightening process between air-cooling self-tempering process and surface treatment process: 1-3 passes of cold straightening, straightening speed 0.1-0.5 m / s, straightening temperature M s - (420-360) °C, maximum reduction ≤ 6 mm; wherein M S The following formula is used to calculate the temperature in °C, with the element symbols representing the mass percentage of the corresponding element in the strand: M S = 539 - 423 C - 11 Si - 30.4 Mn - 12.1 Cr - 17.7 Ni - 7.5 Mo.

10. The method of producing a steel plate for shipbuilding and offshore engineering according to claim 1, characterized in that, the chemical composition of the steel plate further satisfies any one, two, three or all of the following conditions: CEV=C+Mn / 6+(Cr+Mo) / 5+(Cu+Ni) / 15 is 0.227-0.604; Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15 is 0.107-0.276; Ni / Cu is 0.95-1.05; 5C+Si+Mn+Cr+Ni+Mo+Cu is 1.46-4.13; wherein the element symbols in the formulas represent the mass percent of the corresponding elements.

11. The method of producing a steel plate for shipbuilding and offshore engineering according to claim 1, characterized in that, In the casting blank heating process, the heat recovery temperature is less than or equal to 800 DEG C, the preheating temperature is less than or equal to 900 DEG C, the first heating temperature is 970 DEG C to 1030 DEG C, the second heating section temperature is 1070 DEG C to 1130 DEG C, and the total heating time length is 0.019 h / mm to 0.023 h / mm of the casting blank thickness.

12. The method of producing a steel plate for shipbuilding and offshore engineering according to claim 11, characterized in that, In the casting blank heating process, the casting blank charging temperature ≥ M S -350℃, M S The following formula is used for calculation, unit: ℃, the element symbol in the formula represents the mass percentage of the corresponding element in the casting blank; M S = 539 - 423 C - 11 Si - 30.4 Mn - 12.1 Cr - 17.7 Ni - 7.5 Mo.

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