Method for producing a bridge steel plate with controlled residual stresses

Abstract

This invention discloses a method for producing bridge steel plates with controlled residual stress. The steel plates are designed using a low-alloy, low-stress composition system. The production method includes a sequential process of billet heating, hot rolling, controlled water cooling, and tempering heat treatment. In the tempering heat treatment process: the steel plate thickness is 6-20 mm, and the tempering temperature is B... s +(-65~55)℃; or steel plate thickness 20~50mm, tempering temperature B s +(-85~35)℃; or if the thickness of the steel plate is >50mm, the tempering temperature B s +(-105~15)℃; the tempering and holding time t1 is controlled according to (T+273.15)×(20+lg(t1 / 60)) / 1000≥13.7, where t1 is in minutes. This effectively controls and reduces residual stress, taking into account the steel plate's microstructure, properties, processing efficiency, and cost, which is of great significance for improving the safety of bridge structures.

Description

Technical Field

[0001] This invention belongs to the field of steel material preparation technology, and relates to a method for producing bridge steel plates with controlled residual stress. Background Technology

[0002] The generation of residual stress is an unavoidable problem during the manufacturing and use of bridge steel plates.

[0003] Residual stress refers to the self-balancing stress that exists inside a material in the absence of external forces. It mainly originates from the processing of bridge steel plates, such as hot working, cold forming, and welding.

[0004] Residual stress has a significant impact on the performance and service life of bridge structures. First, residual stress can lead to deformation of the bridge structure, affecting its geometry and dimensional accuracy, and consequently impacting the overall performance and safety of the bridge. Second, the presence of residual stress reduces the fatigue strength of the bridge structure, increases the initiation and propagation of fatigue cracks, and thus shortens the bridge's service life. Furthermore, residual stress can also lead to localized stress concentration, further exacerbating the risk of structural damage and failure. Summary of the Invention

[0005] In order to solve the problem of residual stress in the prior art, the present invention aims to provide a bridge steel plate and a method for producing a bridge steel plate that controls residual stress.

[0006] To achieve the above-mentioned objective, one embodiment of the present invention provides a bridge steel plate. The chemical composition of the steel plate, by mass percentage, includes: C 0.04~0.13%, Si 0.11~0.21%, Mn 1.17~1.45%, Cr 0~0.30%, Ni 0.06~0.30%, Mo 0~0.30%, Cu 0~0.30%, Nb 0.012~0.040%, Ti 0.010~0.018%, Al 0.024~0.048%, P≤0.0200%, S≤0.0050%, O≤0.0025%, N≤0.0048%, H≤0.00018%, with the remainder being iron and unavoidable impurities.

[0007] 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:

[0008] ①CEV=C+Mn / 6+(Cr+Mo) / 5+(Cu+Ni) / 15 is 0.239~0.532;

[0009] ②Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15 is 0.103~0.265;

[0010] ③ The Ni / Cu ratio is 0.95~1.05;

[0011] ④5C+Si+Mn+Cr+Ni+Mo+Cu is 1.54~3.51;

[0012] In each formula, the element symbol represents the mass percentage of the corresponding element.

[0013] 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 is ≤30MPa.

[0014] Preferably, the R of the steel plate m ≥490MPa, R eL ≥345MPa, A≥16%, R eL / R m ≤0.87, Z-direction reduction of area ≥40%.

[0015] Preferably, the microstructure of the steel plate is polygonal ferrite + pearlite / acicular ferrite + tempered bainite + decomposed MA, and the total volume percentage of polygonal ferrite, pearlite / acicular ferrite, tempered bainite and decomposed MA is 100%, and the average grain size of the steel plate is 3~20μm.

[0016] To achieve the above-mentioned objective, one embodiment of the present invention provides a method for producing bridge steel plates. The chemical composition of the steel plate, by mass percentage, includes: C 0.04~0.13%, Si 0.11~0.21%, Mn 1.17~1.45%, Cr 0~0.30%, Ni 0.06~0.30%, Mo 0~0.30%, Cu 0~0.30%, Nb 0.012~0.040%, Ti 0.010~0.018%, Al 0.024~0.048%, P≤0.0200%, S≤0.0050%, O≤0.0025%, N≤0.0048%, H≤0.00018%, with the remainder being iron and unavoidable impurities;

[0017] The production method includes sequential steps.

[0018] Billet heating process: soaking temperature is T NbC +(100~150)℃, 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 +(60~100)℃, final rolling temperature T nr +(10~50)℃, the reduction in each pass is ≤30mm, and the reduction in the non-widening primary rolling pass is ≥20mm; during intermediate billet cooling, the intermediate billet thickness is 2.5~3.0 times the target thickness of the steel plate, and the final cooling temperature A r3 +(20~110)℃, cooling time ≥60s; during the second stage of rolling, the initial rolling temperature A r3 +(10~100)℃, final rolling temperature A r3 +(-30~60)℃, hold for 8~10s before the last rolling pass;

[0020] Controlling the water cooling process: Inlet water temperature A r3 +(-70~30)℃, outlet water temperature B s +(-140~80)℃, cooling rate 8~20℃ / s;

[0021] Tempering heat treatment process: The thickness d of the steel plate is 6~20mm, and the tempering temperature T is B. s +(-65~55)℃; or, the thickness d of the steel plate is 20~50mm, and the tempering temperature T is B. s +(-85~35)℃; or, if the thickness d of the steel plate is greater than 50mm, the tempering temperature T is B. s +(-105~15)℃; 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;

[0022] 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.

[0023] T NbC =7700 / (3.18-lg(Nb×C 0.87 ))-273.15;

[0024] T nr =887+464C-357Si+6445Nb-644 +890Ti+363Al;

[0025] A r3 =910-203 -11Si-15.2Mn-30Cr-13Ni-40Mo;

[0026] B s =550-160C-10Mn-10Cr-10Ni-5Mo.

[0027] Preferably, the tempering heat treatment process has a heating rate of 8~15℃ / min.

[0028] Preferably, the tempering heat treatment process involves tempering in a tempering furnace while maintaining a nitrogen atmosphere.

[0029] 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℃.

[0030] Preferably, the production method further includes a surface treatment step between the controlled water cooling step and the tempering heat treatment step: after the steel plate is cooled to room temperature, the steel plate is surface treated by shot blasting or shot peening.

[0031] Preferably, the surface treatment process:

[0032] The shot blasting or shot peening time t and the steel plate thickness d satisfy t=k×d+C, where t is in min, k is 0.1~0.2min / mm, and C is 5~7min.

[0033] Preferably, the surface treatment process:

[0034] The shot blasting or shot peening rate P and the thickness d of the steel plate satisfy P=k1×d+C1, where the unit of P is kg / min, k1 is 0.4~0.6kg / (min·mm), and C1 is 160~200kg / min.

[0035] Preferably, the surface treatment process:

[0036] The shot blasting or shot peening velocity S and the steel plate thickness d satisfy S=k2×d+C2, where S is in m / s, k2 is 0.1~0.3m / (s·mm), and C2 is 65~75m / s.

[0037] Preferably, the production method further includes an air cooling process between the water cooling process and the tempering heat treatment process: after the steel plate exits the water, it undergoes air cooling, with the upper cooling bed temperature B... s +(-150~200)℃, lower cooling bed temperature M s -(260~150)℃.

[0038] Preferably, the production method further includes a temperature-controlled preheating and straightening process between the hot rolling process and the controlled water cooling process: performing at least one pass of preheating and straightening, with a straightening speed of 0.1~1.5 m / s and a straightening temperature A. r3 +(-65~25)℃, maximum reduction ≤4mm.

[0039] Preferably, during the second stage of rolling, the reduction in each pass is ≤20mm, and the reduction in the last pass is ≤3mm.

[0040] Preferably, the chemical composition of the steel plate, by mass percentage, also satisfies any one, two, three, or all of the following conditions:

[0041] CEV = C + Mn / 6 + (Cr + Mo) / 5 + (Cu + Ni) / 15 is 0.239~0.532;

[0042] Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15 is 0.103~0.265;

[0043] The Ni / Cu ratio is 0.95~1.05;

[0044] 5C+Si+Mn+Cr+Ni+Mo+Cu is 1.54~3.51;

[0045] In the formula, the element symbols represent the mass percentage of the corresponding element.

[0046] Preferably, the billet heating process includes heat recovery, preheating, primary heating, secondary heating and homogenization. The heat recovery temperature is ≤850℃, the preheating temperature is ≤950℃, the primary heating temperature is 1020~1080℃, the secondary heating temperature is 1120~1180℃, and the total heating time is 0.019~0.023h / mm billet thickness.

[0047] Compared with the prior art, the beneficial effects of one embodiment of this application are as follows:

[0048] The design employs a low-alloy composition system and optimizes the microstructure and mechanical properties of the steel plate by controlling the homogenization temperature, homogenization time, temperature, reduction and residence time during hot rolling, water cooling temperature and cooling rate, and tempering heat treatment operations. In particular, it involves the coordinated control of tempering temperature T and tempering holding time t1, with precise control of tempering temperature T based on different thicknesses. This approach improves the ductility and toughness of the steel plate, such as impact toughness, while ensuring sufficient strength. It also reduces poor surface and core properties, such as hardness. Furthermore, it significantly reduces residual stress, improves residual stress distribution, and ensures that the steel plate is less prone to deformation and cracking during subsequent pipe manufacturing.

[0049] In this way, the effective control and reduction of residual stress in bridge steel plates, while taking into account the steel plate structure, performance, processing efficiency and cost, is of great significance for improving the safety of bridge structures. Attached Figure Description

[0050] Figure 1 This is a metallographic diagram of the steel plate of Experimental Example 1 of the present invention;

[0051] Figure 2 This is a metallographic diagram of the steel plate of Experimental Example 1A of the present invention;

[0052] Figure 3 This is a metallographic diagram of the steel plate of Experimental Example 1B of the present invention;

[0053] Figure 4 This is a metallographic diagram of the steel plate of Experimental Example 1C of the present invention;

[0054] Figure 5 This is a metallographic diagram of the steel plate of Experimental Example 1D of the present invention;

[0055] Figure 6 This is a metallographic diagram of the steel plate of Experimental Example 1E of the present invention. Detailed Implementation

[0056] 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.

[0057] One embodiment of the present invention provides a bridge steel plate.

[0058] The chemical composition of the steel plate, by mass percentage, includes: C 0.04~0.13%, Si 0.11~0.21%, Mn 1.17~1.45%, Cr 0~0.30%, Ni 0.06~0.30%, Mo 0~0.30%, Cu 0~0.30%, Nb 0.012~0.040%, Ti 0.010~0.018%, Al 0.024~0.048%, P≤0.0200%, S≤0.0050%, O≤0.0025%, N≤0.0048%, H≤0.00018%, with the remainder being iron and unavoidable impurities.

[0059] The following is a detailed analysis and explanation of the main functions of each element and the selection of its dosage.

[0060] C: Carbon is the most economical strengthening element in steel, providing solid solution strengthening. It also forms carbides with niobium, titanium, chromium, molybdenum, etc., resulting in 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 0.04~0.13%.

[0061] Preferably, the carbon content can be controlled at any one of 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, and 0.13%.

[0062] 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 0.11~0.21%.

[0063] Preferably, the silicon content can be controlled at any one of 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, and 0.21%.

[0064] 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 1.17~1.45%.

[0065] Preferably, the manganese content can be controlled at any one of 1.17%, 1.18%, 1.20%, 1.22%, 1.24%, 1.25%, 1.30%, 1.31%, 1.33%, 1.35%, 1.37%, 1.39%, 1.40%, and 1.45%.

[0066] Cr: Chromium plays a solid solution strengthening role in steel, significantly improving its hardenability and hardness. Chromium can form stable carbides and increase 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 0~0.30%.

[0067] 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.

[0068] Preferably, in another embodiment, chromium is added, and the chromium content can be controlled at 0.18~0.30%.

[0069] Preferably, the chromium content can be controlled at any one of 0.18%, 0.20%, 0.22%, 0.25%, 0.27%, 0.29%, and 0.30%.

[0070] 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 also improve the toughness of steel and reduce stress concentration. In this application, the nickel content is controlled at 0.06~0.30%.

[0071] 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%, and 0.30%.

[0072] 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 0~0.30%.

[0073] 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.

[0074] Preferably, in another embodiment, molybdenum is added, and the molybdenum content is controlled at 0.05~0.30%.

[0075] 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 0.30%.

[0076] 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 0~0.30%.

[0077] 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.

[0078] Preferably, in another embodiment, copper is added, and the copper content is controlled at 0.10~0.30%.

[0079] Preferably, the copper content can be controlled at any one of 0.06%, 0.08%, 0.10%, 0.15%, 0.20%, 0.21%, 0.23%, 0.25%, 0.29%, and 0.30%.

[0080] 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 0.012~0.040%.

[0081] Preferably, the niobium content can be controlled at any one of 0.012%, 0.015%, 0.018%, 0.019%, 0.021%, 0.024%, 0.026%, 0.030%, 0.031%, 0.034%, 0.036%, 0.038%, and 0.040%.

[0082] 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 0.010~0.018%.

[0083] Preferably, the titanium content can be controlled at any one of 0.010%, 0.014%, 0.015%, 0.016%, and 0.018%.

[0084] 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 lead to discontinuous microstructure and stress concentration. In this application, the aluminum content is controlled at 0.024~0.048%.

[0085] Preferably, the aluminum content can be controlled at any one of 0.024%, 0.025%, 0.028%, 0.030%, 0.033%, 0.035%, 0.038%, 0.040%, 0.042%, 0.045%, and 0.048%.

[0086] 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 ≤0.0200%, S ≤0.0050%, O ≤0.0025%, N ≤0.0048%, and H ≤0.00018%.

[0087] Preferably, the P content is controlled at 0.0150% or less, 0.0120% or less, and can also be controlled at 0.0060% or more.

[0088] Preferably, the sulfur content is controlled at 0.0050% or less, 0.0040% or less, or even 0.0005% or more.

[0089] Preferably, the nitrogen content is controlled at 0.0022% or more.

[0090] Preferably, the O content is controlled at 0.0011% or more.

[0091] Preferably, the H content is controlled at 0.00005% or more.

[0092] 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:

[0093] ①CEV=C+Mn / 6+(Cr+Mo) / 5+(Cu+Ni) / 15 is 0.239~0.532;

[0094] ②Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15 is 0.103~0.265;

[0095] ③ The Ni / Cu ratio is 0.95~1.05;

[0096] ④5C+Si+Mn+Cr+Ni+Mo+Cu is 1.54~3.51.

[0097] 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.

[0098] Furthermore, the residual stress of the steel plate is ≤80MPa.

[0099] 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.

[0100] Furthermore, the steel plate exhibits small fluctuations and uniform distribution of residual stress throughout the plate.

[0101] For example, the residual stress difference between any two points in the head, middle, tail, upper, and lower parts is ≤30MPa.

[0102] 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".

[0103] In this embodiment, the thickness d of the steel plate is ≥ 6 mm.

[0104] Furthermore, the steel plate possesses excellent mechanical properties:

[0105] R m ≥490MPa;

[0106] R eL ≥345MPa;

[0107] A≥16%;

[0108] R eL / R m ≤0.87;

[0109] Z-direction reduction of area ≥40%.

[0110] 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".

[0111] The steel plate has excellent toughness and satisfies any one or any combination of the following conditions:

[0112] Impact energy at 0℃ KV2≥250J;

[0113] Impact energy at -20℃ KV2≥220J;

[0114] Impact energy at -40℃ KV2≥200J;

[0115] -60℃ impact energy KV2≥180J;

[0116] ductile-brittle transition temperature T t50%US ≤-80℃;

[0117] At 0℃, the crack tip opening displacement of CTOD is ≥0.6mm;

[0118] At -20℃, the crack tip opening displacement of CTOD is ≥0.4mm;

[0119] At -40℃, the crack tip opening displacement of CTOD is ≥0.3mm.

[0120] 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".

[0121] In addition, the steel plate has excellent shape, with an unevenness of ≤3mm / m.

[0122] Furthermore, in one embodiment, the microstructure of the steel plate is polygonal ferrite + pearlite + tempered bainite + decomposed MA, and the total volume percentage of polygonal ferrite, pearlite, tempered bainite and decomposed MA is 100%.

[0123] In another embodiment, the microstructure of the steel plate is polygonal ferrite + acicular ferrite + tempered bainite + decomposed MA, and the total volume percentage of polygonal ferrite, acicular ferrite, tempered bainite and decomposed MA is 100%.

[0124] The average grain size of the steel plate is 3~20μm.

[0125] Furthermore, one embodiment of the present invention also provides a method for producing the steel plate. This method can be used to prepare a bridge steel plate with low and uniform residual stress.

[0126] The production method includes a sequential process of billet heating, hot rolling, controlled water cooling, and tempering heat treatment to process the billet into the steel plate.

[0127] The following sections will describe each process in detail in order.

[0128] <Bill Heating Process>

[0129] In this process, the billet is sent into a heating furnace for heating.

[0130] The billet can be either a continuously cast billet or a mold-cast billet; this application does not specify either.

[0131] The thickness of the cast billet is preferably above 200mm, for example, 220~320mm.

[0132] The chemical composition of the billet is consistent with that of the steel plate prepared therefrom.

[0133] In this process, the soaking temperature is T. NbC +(100~150)℃, heat soaking time ≥25min.

[0134] 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.

[0135] 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.

[0136] Preferably, the heat spreader temperature is T. NbC +100℃, T NbC +110℃, T NbC +115℃, T NbC +120℃, T NbC +125℃, T NbC Any value of +150℃.

[0137] 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.

[0138] The heat recovery temperature is ≤850℃, the preheating temperature is ≤950℃, the first heating temperature is 1020~1080℃, the second heating temperature is 1120~1180℃, 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.

[0139] Furthermore, the furnace entry temperature of the billet is ≥ M S -300℃.

[0140] 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.

[0141] <Hot Rolling Process>

[0142] 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.

[0143] The thickness d of the steel plate is, for example, 6~100mm.

[0144] During the first stage of rolling, the initial rolling temperature T nr +(60~100)℃, final rolling temperature T nr +(10~50)℃, the reduction of each pass is ≤30mm, and the reduction of the non-widening primary rolling pass is ≥20mm.

[0145] 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.

[0146] Furthermore, the first stage of rolling includes several passes, some of which are widening passes and others are non-widening passes. The reduction in each pass does not exceed 30 mm; while the reduction in the initial rolling pass (i.e., the first non-widening pass) among the multiple non-widening passes is ≥20 mm.

[0147] The thickness of the intermediate billet obtained through the first stage of rolling is 2.5 to 3.0 times the target thickness of the steel plate.

[0148] Thus, rolling at a higher temperature range can reduce the resistance to rolling deformation and increase the rolling reduction, which is conducive to deformation penetration into the core of the billet and improve 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. Moreover, by controlling the reduction of each pass and having a larger reduction in the initial rolling pass of the non-widening pass, the as-cast structure can be fully broken down to obtain refined recrystallized grains, while avoiding a sharp increase in internal stress.

[0149] The target thickness of the steel plate is the final thickness d of the steel plate.

[0150] Preferably, during the first stage of rolling, the initial rolling temperature is T. nr +60℃, T nr +65℃, T nr +70℃, T nr +75℃, T nr +80℃, T nr +85℃, T nr +90℃, T nr +95℃, T nr Any value within +100℃.

[0151] Preferably, during the first stage of rolling, the final rolling temperature is T. nr +10℃, T nr +20℃, T nr +30℃, T nr +40℃, T nr Any value within +50℃.

[0152] Furthermore, during the cooling of the intermediate billet, the intermediate billet is cooled to a final cooling temperature A. r3 +(20~110)℃, cooling time ≥60s.

[0153] 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.

[0154] 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 cooling process can be avoided, which would lead to a decrease in low-temperature toughness. More importantly, it allows for sufficient recrystallization and releases certain internal stresses at high temperatures.

[0155] Preferably, the final cooling temperature is A.r3 +20℃, A r3 +30℃, A r3 +40℃, A r3 +50℃, A r3 +60℃, A r3 +70℃, A r3 +80℃, A r3 +90℃, A r3 +100℃, A r3 Any value within +110℃.

[0156] More preferably, the intermediate billet can be cooled by air cooling.

[0157] Next, during the second stage of rolling, the initial rolling temperature A r3 +(10~100)℃, final rolling temperature A r3 +(-30~60)℃, hold for 8~10s before the last rolling pass.

[0158] Preferably, during the second stage of rolling, the initial rolling temperature is A. r3 +10℃, A r3 +20℃, A r3 +30℃, A r3 +40℃, A r3 +45℃, A r3 +50℃, A r3 +60℃, A r3 +70℃, A r3 +80℃, A r3 +90℃, A r3 Any value within +100℃.

[0159] Preferably, during the second stage of rolling, the final rolling temperature is A. r3 -30℃, A r3 -20℃, A r3 -15℃, A r3 -5℃, A r3 A r3 +10℃, A r3 +20℃, A r3 +30℃, A r3 +40℃, A r3 +50℃, A r3 Any value within +60℃.

[0160] 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.

[0161] Preferably, during the second stage of rolling, the reduction in each pass is ≤20mm, and the reduction in the last pass is ≤3mm.

[0162] 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.

[0163] <Controlled Water Cooling Process>

[0164] In this process, the rolled steel plate is cooled by water.

[0165] In this process, the water inlet temperature A r3 +(-70~30)℃, outlet water temperature B s +(-140~80)℃, cooling rate 8~20℃ / s.

[0166] 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.

[0167] 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.

[0168] Preferably, the water temperature is A r3 -70℃, A r3 -60℃, A r3 -50℃, A r3 -40℃, A r3 -30℃, A r3 -20℃, A r3 A r3 +10℃, A r3 +20℃, A r3 Any value within +30℃.

[0169] Preferably, the outlet water temperature is B s -140℃, B s -120℃, B s -100℃, B s -80℃, B s -60℃, B s -40℃, B s -20℃, B sB s +20℃, B s +40℃, B s +60℃, B s Any value within +80℃.

[0170] Preferably, the cooling rate is any value among 8℃ / s, 10℃ / s, 12℃ / s, 14℃ / s, 15℃ / s, 16℃ / s, 18℃ / s, and 20℃ / s.

[0171] Preferably, in this process, the steel plate is water-cooled using an ultra-fast cooling system.

[0172] The optimal roller speed of the ultra-fast cooling system is controlled at 0.6~1.8m / s, water pressure at 0.15~0.25MPa, and water-to-water ratio at 0.88~0.94.

[0173] 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.

[0174] 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.

[0175] 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.

[0176] 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 X3The values ​​are 0.50~0.60, 0.60~0.70, and 0.70~0.80 respectively.

[0177] <Tempering heat treatment process>

[0178] In this process, for the steel plate with a thickness d of 6~20mm, the tempering temperature T is B. s +(-65~55)℃.

[0179] For the steel plate with a thickness d of 20~50mm, the tempering temperature T is B. s +(-85~35)℃.

[0180] For the steel plate with a thickness d > 50 mm, the tempering temperature T is B. s +(-105~15)℃.

[0181] Furthermore, the tempering and heat preservation time t1 is controlled according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥13.7, where t1 is in minutes.

[0182] In other words, by coordinating and controlling the tempering temperature T and the tempering holding time t1, and further precisely controlling the tempering temperature T according to different thicknesses, the microstructure and various mechanical properties of the steel plate can be optimized. While ensuring sufficient strength, the plasticity and toughness of the steel plate, such as impact toughness, can be improved. Poor surface properties of the steel plate, such as hardness, can be reduced. Moreover, residual stress can be significantly reduced and its distribution improved, ensuring that the plate is less prone to deformation and cracking during subsequent pipe manufacturing. Furthermore, the problem of excessive energy consumption and production costs caused by the introduction of tempering heat treatment can be avoided.

[0183] Preferably, the heating rate is 8~15℃ / min.

[0184] Preferably, in this process, tempering heat treatment can be carried out in a tempering furnace, where a nitrogen atmosphere can be maintained.

[0185] 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.

[0186] In summary, one embodiment of the present invention improves the plasticity and toughness of steel plates, such as impact toughness, by controlling the homogenization temperature, homogenization time, temperature during hot rolling, water cooling temperature and cooling rate, and tempering heat treatment, while ensuring sufficient strength margin; reduces poor core and surface properties of steel plates, such as hardness; and further significantly reduces residual stress and improves residual stress distribution.

[0187] As a preferred embodiment, the production method may further include any one, any combination of, or all of the following processes: air cooling process, surface treatment process, tempering and stacking process, and temperature-controlled preheating and straightening process.

[0188] The following sections will provide a detailed introduction to each process.

[0189] <Air Cooling Process>

[0190] This process is located between the controlled water cooling process and the tempering heat treatment process.

[0191] Specifically, after the steel plate is removed from the water, it is air-cooled 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] This process is located between the controlled water cooling process and the tempering heat treatment process. In embodiments with an air cooling process, this process is located between the air cooling process and the tempering heat treatment process.

[0200] Specifically, after the steel plate is cooled to room temperature, the steel plate is surface treated by shot blasting or shot peening.

[0201] Thus, by shot blasting or shot peening the steel plate cooled to room temperature, surface compressive stress can be achieved, which can then counteract the residual tensile stress inside the steel plate, thereby reducing residual stress and improving the distribution of residual stress.

[0202] In this process, the shot blasting or shot peening time t and the steel plate thickness d satisfy t=k×d+C.

[0203] Where t is in min, k is 0.1~0.2 min / mm, and C is 5~7 min.

[0204] In this process, the shot blasting amount P and the thickness d of the steel plate satisfy P=k1×d+C1.

[0205] Where P is in kg / min, k1 is 0.4~0.6 kg / (min·mm), and C1 is 160~200 kg / min.

[0206] In this process, the shot blasting or shot peening speed S and the steel plate thickness d satisfy S=k2×d+C2.

[0207] Where S is in m / s, k2 is 0.1~0.3m / (s·mm), and C2 is 65~75m / s.

[0208] In this way, by jointly controlling the time t, the shot blasting amount or shot peening amount P, the speed S and the plate thickness d respectively, a uniform compressive stress layer can be formed on the surface of the steel plate, and the formed compressive stress can greatly eliminate residual tensile stress, thereby achieving the effect of reducing residual stress and improving residual stress distribution.

[0209] 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.

[0210] 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.

[0211] 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.

[0212] 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.

[0213] Furthermore, the shot blasting or shot peening angle is 45°~80°, with a coverage rate of 100%.

[0214] <Stacking process after tempering>

[0215] This process occurs after the tempering heat treatment process.

[0216] 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.

[0217] Among them, stacking temperature B s -(210~110)℃, cooling rate 10~30℃ / h, destacking temperature ≤B s -450℃.

[0218] Thus, by rapidly removing and stacking materials, and by controlling the cooling rate, the distribution of residual stress is made more uniform.

[0219] Preferably, the stacking time is 12~24h.

[0220] <Temperature Controlled Preheating and Straightening Process>

[0221] This process is located between the hot rolling process and the controlled water cooling process.

[0222] Specifically, the steel plate obtained from the hot rolling process is subjected to at least one pass of preheating and straightening.

[0223] The straightening speed is 0.1~1.5 m / s, and the straightening temperature is A. r3 +(-65~25)℃, maximum reduction ≤4mm.

[0224] 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.

[0225] Preferably, in this process, the straightening temperature is A. r3 -65℃, A r3 -60℃, A r3 -55℃, A r3 -50℃, A r3 -45℃, A r3 -40℃, A r3 -35℃, A r3 -30℃, A r3 -25℃, A r3 -20℃, A r3 -15℃, A r3 -10℃, A r3 -5℃, A r3 A r3 +5℃, A r3 +10℃, A r3 +15℃, A r3 +20℃, A r3 Any value within +25℃.

[0226] 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.

[0227] First Embodiment

[0228] This embodiment provides a bridge steel plate and its production method. Specifically, the steel plate is a Q345q grade or 345MPa grade bridge steel plate.

[0229] The chemical composition of the steel plate, by mass percentage, includes: C 0.09~0.13%, Si 0.11~0.21%, Mn 1.37~1.45%, Ni 0.06~0.14%, Nb 0.012~0.020%, Ti 0.010~0.018%, Al 0.024~0.048%, P 0.0100~0.0200%, S 0.0010~0.0050%, O 0.0011~0.0025%, N 0.0022~0.0048%, H 0.00005~0.00018%, with the remainder being iron and unavoidable impurities.

[0230] Furthermore, the chemical composition of the steel plate, by mass percentage, also satisfies the following: CEV is 0.322~0.381, Pcm is 0.163~0.212, and 5C+Si+Mn+Cr+Ni+Mo+Cu is 1.99~2.45.

[0231] Furthermore, the residual stress of the steel plate is ≤40MPa.

[0232] 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.

[0233] In this embodiment, the thickness d of the steel plate is ≥ 6 mm. For example, the thickness d is 6~100 mm.

[0234] In this embodiment, the steel plate exhibits excellent mechanical properties:

[0235] R m ≥490MPa;

[0236] R eL ≥345MPa;

[0237] A≥21%;

[0238] R eL / R m ≤0.82;

[0239] Z-direction reduction of area ≥40%.

[0240] The steel plate has excellent toughness:

[0241] Impact energy at 0℃ KV2≥250J;

[0242] Impact energy at -20℃ KV2≥220J;

[0243] -40℃ impact energy KV2≥200J;

[0244] -60℃ impact energy KV2≥180J;

[0245] At 0℃, the crack tip opening displacement of CTOD is ≥0.6mm;

[0246] At -20℃, the crack tip opening displacement of CTOD is ≥0.4mm;

[0247] At -40℃, the crack tip opening displacement of CTOD is ≥0.3mm.

[0248] In addition, the steel plate has excellent shape, with an unevenness of ≤1mm / m.

[0249] Furthermore, the microstructure of the steel plate is polygonal ferrite + pearlite + tempered bainite + decomposed MA, and the total volume percentage of polygonal ferrite, pearlite, tempered bainite and decomposed MA is 100%.

[0250] Among them, polygonal ferrite accounts for 65-75% of the volume, pearlite accounts for 20-25% of the volume, tempered bainite accounts for 0-8% of the volume, and decomposed MA accounts for 0-7% of the volume.

[0251] The average grain size of the steel plate is 12~20μm.

[0252] Furthermore, the production method includes a sequential billet heating process, a hot rolling process, an optional temperature-controlled preheating and straightening process, a controlled water cooling process, an optional air cooling process, an optional surface treatment process, a tempering heat treatment process, and an optional post-tempering stacking process, to process the billet into the steel plate.

[0253] The following sections will describe each process in detail in order.

[0254] <Bill Heating Process>

[0255] The thickness of the cast billet is above 200mm, for example, 220~320mm.

[0256] The heat spreader temperature is T NbC +(100~150)℃, heat soaking time ≥25min.

[0257] 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.

[0258] The heat recovery temperature is ≤850℃, the preheating temperature is ≤950℃, the first heating temperature is 1020~1080℃, the second heating temperature is 1120~1180℃, and the total heating time is 0.019~0.023h / mm billet thickness.

[0259] Furthermore, the furnace entry temperature of the billet is ≥ M S -300℃.

[0260] <Hot Rolling Process>

[0261] 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.

[0262] The thickness d of the steel plate is, for example, 6~100mm.

[0263] During the first stage of rolling, the initial rolling temperature T nr +(60~100)℃, final rolling temperature T nr +(10~50)℃, the reduction of each pass is ≤30mm, and the reduction of the non-widening primary rolling pass is ≥20mm.

[0264] During the cooling of the intermediate billet, the thickness of the intermediate billet is 2.5 to 3.0 times the target thickness of the steel plate.

[0265] Furthermore, during the cooling of the intermediate billet, the intermediate billet is cooled to a final cooling temperature A. r3 +(90~110)℃, cooling time ≥60s.

[0266] Intermediate billets can be cooled by air cooling.

[0267] Next, during the second stage of rolling, the initial rolling temperature A r3 +(80~100)℃, final rolling temperature A r3 +(40~60)℃, hold for 8~10s before the last rolling pass.

[0268] Furthermore, during the second stage of rolling, the reduction in each pass is ≤20mm, and the reduction in the final pass is ≤3mm.

[0269] <Optional temperature-controlled preheating and straightening process>

[0270] 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.

[0271] Specifically, the steel plate obtained from the hot rolling process is subjected to at least one pass of preheating and straightening.

[0272] The straightening speed is 0.1~1.5 m / s, and the straightening temperature is A. r3 +(-65~25)℃, maximum reduction ≤4mm.

[0273] <Controlled Water Cooling Process>

[0274] In this process, the rolled steel plate is cooled by water in an ultra-fast cooling system.

[0275] Inlet water temperature Ar3 +(10~30)℃, outlet water temperature B s +(40~80)℃, cooling rate 8~20℃ / s.

[0276] The roller speed of the ultra-fast cooling system is preferably controlled at 0.5~1.5m / s.

[0277] Furthermore, in an optional implementation, the cooling manifold in the ultrafast cooling system can be controlled in either the intermittent manner or the head-and-tail shielding manner.

[0278] <Optional air cooling process>

[0279] In this process, the steel plate is cooled by air cooling on a cooling bed, during which self-tempering occurs.

[0280] upper cooling bed temperature B s +(-150~200)℃.

[0281] Furthermore, in this process, the temperature of the lower cooling bed for the steel plate does not exceed M. s -150℃.

[0282] Preferably, the temperature M of the lower cooling bed s -(260~150)℃.

[0283] <Optional surface treatment process>

[0284] After the steel plate is cooled to room temperature, it is surface treated by shot blasting or shot peening.

[0285] During this period, one, two, or all of the following three conditions must be met:

[0286] Condition 1, t=k×d+C;

[0287] Condition 2, P = k1 × d + C1;

[0288] Condition 3: S = k2 × d + C2.

[0289] 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;

[0290] 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.

[0291] 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.

[0292] 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.

[0293] 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.

[0294] Furthermore, the shot blasting or shot peening angle is 45°~80°, with a coverage rate of 100%.

[0295] <Tempering heat treatment process>

[0296] In this process, for the steel plate with a thickness d of 6~20mm, the tempering temperature T is B. s +(35~55)℃.

[0297] For the steel plate with a thickness d of 20~50mm, the tempering temperature T is B. s +(15~35)℃.

[0298] For the steel plate with a thickness d > 50 mm, the tempering temperature T is B. s +(-5~15)℃.

[0299] The tempering and heat preservation time t1 is controlled according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥16.0, where t1 is in minutes.

[0300] Preferably, the heating rate is 8~15℃ / min.

[0301] Preferably, in this process, tempering heat treatment can be carried out in a tempering furnace, where a nitrogen atmosphere can be maintained.

[0302] <Optional post-tempering stacking process>

[0303] This process occurs after the tempering heat treatment process.

[0304] 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.

[0305] Among them, stacking temperature B s -(210~110)℃, cooling rate 10~30℃ / h, destacking temperature ≤B s -450℃.

[0306] Preferably, the stacking time is 12~24h.

[0307] The following are some experimental examples of this embodiment.

[0308] First, Table 1 shows the chemical composition of the steel plates in several test examples.

[0309] [Table 1]

[0310]

[0311] 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 and 3. " / " indicates that the corresponding process was not performed.

[0312] [Table 2]

[0313]

[0314] [Table 3]

[0315]

[0316] The microstructure and properties of the steel plates described in each test example were tested, and the results are shown in Tables 4 and 5. Additionally, Figure 1 The metallographic structure of Experimental Example 1 is shown.

[0317] [Table 4]

[0318]

[0319] [Table 5]

[0320]

[0321] Second Embodiment

[0322] This embodiment provides a bridge steel plate and its production method. Specifically, the steel plate is a Q370q grade or 370MPa grade bridge steel plate.

[0323] 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.

[0324] In this embodiment, the chemical composition of the steel plate, by mass percentage, includes: C 0.08~0.12%, Si 0.11~0.21%, Mn 1.32~1.40%, Ni 0.10~0.18%, Cu 0.10~0.18%, Nb 0.015~0.023%, Ti 0.010~0.018%, Al 0.024~0.048%, P 0.0100~0.0200%, S 0.0010~0.0050%, O 0.0011~0.0025%, N 0.0022~0.0048%, H 0.00005~0.00018%, with the remainder being iron and unavoidable impurities.

[0325] Furthermore, the chemical composition of the steel plate, by mass percentage, also satisfies the following: CEV 0.313~0.377, Pcm 0.156~0.209, Ni / Cu 0.95~1.05, and 5C+Si+Mn+Cr+Ni+Mo+Cu 2.03~2.57.

[0326] Furthermore, the residual stress of the steel plate is ≤40MPa.

[0327] 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.

[0328] In this embodiment, the thickness d of the steel plate is ≥ 6 mm. For example, the thickness d is 6~100 mm.

[0329] In this embodiment, the steel plate exhibits excellent mechanical properties:

[0330] R m ≥510MPa;

[0331] R eL ≥370MPa;

[0332] A≥20%;

[0333] R eL / R m ≤0.83;

[0334] Z-direction reduction of area ≥40%.

[0335] The steel plate has excellent toughness:

[0336] Impact energy at 0℃ KV2≥260J;

[0337] Impact energy at -20℃ KV2≥240J;

[0338] Impact energy at -40℃ KV2≥220J;

[0339] Impact energy at -60℃ KV2≥200J;

[0340] ductile-brittle transition temperature T t50%US ≤-80℃;

[0341] At 0℃, the crack tip opening displacement of CTOD is ≥0.6mm;

[0342] At -20℃, the crack tip opening displacement of CTOD is ≥0.4mm;

[0343] At -40℃, the crack tip opening displacement of CTOD is ≥0.3mm.

[0344] In addition, the steel plate has excellent shape, with an unevenness of ≤1mm / m.

[0345] Furthermore, the microstructure of the steel plate is polygonal ferrite + acicular ferrite + tempered bainite + decomposed MA, and the total volume percentage of polygonal ferrite, acicular ferrite, tempered bainite and decomposed MA is 100%.

[0346] Among them, polygonal ferrite accounts for 65-75% of the volume, acicular ferrite accounts for 0-5% of the volume, tempered bainite accounts for 15-25% of the volume, and decomposed MA accounts for 5-10% of the volume.

[0347] The average grain size of the steel plate is 8~15μm.

[0348] In this embodiment, some parameters of the following processes differ from those in the first embodiment described above.

[0349] <Hot Rolling Process>

[0350] When the intermediate billet is cooled, the final cooling temperature A r3 +(70~90)℃.

[0351] During the second stage of rolling, the initial rolling temperature A r3 +(60~80)℃, final rolling temperature A r3 +(20~40)℃.

[0352] <Controlled Water Cooling Process>

[0353] Inlet water temperature A r3 +(-10~10)℃, outlet water temperature B s +(10~50)℃.

[0354] <Tempering heat treatment process>

[0355] In this process, for the steel plate with a thickness d of 6~20mm, the tempering temperature T is B. s +(15~35)℃.

[0356] For the steel plate with a thickness d of 20~50mm, the tempering temperature T is B. s +(-5~15)℃.

[0357] For the steel plate with a thickness d > 50 mm, the tempering temperature T is B. s -(25~5)℃.

[0358] The tempering and heat preservation time t1 is controlled according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥15.3, where t1 is in minutes.

[0359] The following are some experimental examples of this embodiment.

[0360] First, Table 6 shows the chemical composition of the steel plates in several test examples.

[0361] [Table 6]

[0362]

[0363] Each test case was prepared using the specific production method of this embodiment, and some parameters of each process are shown in Tables 7 and 8. " / " indicates that the corresponding process was not performed.

[0364] [Table 7]

[0365]

[0366] [Table 8]

[0367]

[0368] The microstructure and properties of the steel plates described in each test example were tested, and the results are shown in Tables 9 and 10. Additionally, Figure 2 The metallographic structure of Experimental Example 1A is shown.

[0369] [Table 9]

[0370]

[0371] [Table 10]

[0372]

[0373] Third Embodiment

[0374] This embodiment provides a bridge steel plate and its production method. Specifically, the steel plate is a 420MPa grade or Q420q grade bridge steel plate.

[0375] 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.

[0376] In this embodiment, the chemical composition of the steel plate, by mass percentage, includes: C 0.07~0.11%, Si 0.11~0.21%, Mn 1.27~1.35%, Ni 0.14~0.22%, Mo 0.05~0.13%, Cu 0.14~0.22%, Nb 0.018~0.026%, Ti 0.010~0.018%, Al 0.024~0.048%, P 0.0090~0.0160%, S 0.0010~0.0040%, O 0.0011~0.0025%, N 0.0022~0.0048%, H 0.00005~0.00018%, with the remainder being iron and unavoidable impurities.

[0377] Furthermore, the chemical composition of the steel plate, by mass percentage, also satisfies the following: CEV is 0.310~0.390, Pcm is 0.150~0.208, Ni / Cu is 0.95~1.05, and 5C+Si+Mn+Cr+Ni+Mo+Cu is 2.06~2.68.

[0378] Furthermore, the residual stress of the steel plate is ≤40MPa.

[0379] 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.

[0380] In this embodiment, the thickness d of the steel plate is ≥ 6 mm. For example, the thickness d is 6~100 mm.

[0381] In this embodiment, the steel plate exhibits excellent mechanical properties:

[0382] R m ≥540MPa;

[0383] R eL ≥420MPa;

[0384] A≥19%;

[0385] R eL / R m ≤0.84;

[0386] Z-direction reduction of area ≥40%.

[0387] The steel plate has excellent toughness:

[0388] Impact energy at 0℃ KV2≥270J;

[0389] Impact energy at -20℃ KV2≥260J;

[0390] Impact energy at -40℃ KV2≥240J;

[0391] Impact energy at -60℃ KV2≥220J;

[0392] ductile-brittle transition temperature T t50%US ≤-80℃;

[0393] At 0℃, the crack tip opening displacement of CTOD is ≥0.6mm;

[0394] At -20℃, the crack tip opening displacement of CTOD is ≥0.4mm;

[0395] At -40℃, the crack tip opening displacement of CTOD is ≥0.3mm.

[0396] In addition, the steel plate has excellent shape, with an unevenness of ≤1mm / m.

[0397] Furthermore, the microstructure of the steel plate is polygonal ferrite + acicular ferrite + tempered bainite + decomposed MA, and the total volume percentage of polygonal ferrite, acicular ferrite, tempered bainite and decomposed MA is 100%.

[0398] Among them, polygonal ferrite accounts for 45-55% of the volume, acicular ferrite accounts for 5-15% of the volume, tempered bainite accounts for 20-30% of the volume, and decomposed MA accounts for 10-20% of the volume.

[0399] The average grain size of the steel plate is 6~12μm.

[0400] In this embodiment, some parameters of the following processes differ from those in the first embodiment described above.

[0401] <Hot Rolling Process>

[0402] When the intermediate billet is cooled, the final cooling temperature A r3 +(50~70)℃.

[0403] During the second stage of rolling, the initial rolling temperature A r3 +(40~60)℃, final rolling temperature A r3 +(0~20)℃.

[0404] <Controlled Water Cooling Process>

[0405] Inlet water temperature A r3 -(30~10)℃, outlet water temperature B s+(-20~20)℃.

[0406] <Tempering heat treatment process>

[0407] In this process, for the steel plate with a thickness d of 6~20mm, the tempering temperature T is B. s +(-5~15)℃.

[0408] For the steel plate with a thickness d of 20~50mm, the tempering temperature T is B. s -(25~5)℃.

[0409] For the steel plate with a thickness d > 50 mm, the tempering temperature T is B. s -(45~25)℃.

[0410] The tempering and heat preservation time t1 is controlled according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥14.9, where t1 is in minutes.

[0411] The following are some experimental examples of this embodiment.

[0412] First, Table 11 shows the chemical composition of the steel plates in several test examples.

[0413] [Table 11]

[0414]

[0415] Each test case was prepared using the specific production method of this embodiment, and some parameters of each process are shown in Tables 12 and 13. " / " indicates that the corresponding process was not performed.

[0416] [Table 12]

[0417]

[0418] [Table 13]

[0419]

[0420] The microstructure and properties of the steel plates described in each test example were tested, and the results are shown in Tables 14 and 15. Additionally, Figure 3 The metallographic structure of Experimental Example 1B is shown.

[0421] [Table 14]

[0422]

[0423] [Table 15]

[0424]

[0425] Fourth embodiment

[0426] This embodiment provides a bridge steel plate and its production method. Specifically, the steel plate is a Q460q grade or 460MPa grade bridge steel plate.

[0427] 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.

[0428] In this embodiment, the chemical composition of the steel plate, by mass percentage, includes: C 0.06~0.10%, Si 0.11~0.21%, Mn 1.22~1.30%, Cr 0.08~0.16%, Ni 0.18~0.26%, Mo 0.08~0.16%, Cu 0.18~0.26%, Nb 0.021~0.029%, Ti 0.010~0.018%, Al 0.024~0.048%, P 0.0090~0.0160%, S 0.0010~0.0040%, O 0.0011~0.0025%, N 0.0022~0.0048%, H 0.00005~0.00018%, with the remainder being iron and unavoidable impurities.

[0429] Furthermore, the chemical composition of the steel plate, by mass percentage, also satisfies the following: CEV is 0.319~0.415, Pcm is 0.146~0.208, Ni / Cu is 0.95~1.05, and 5C+Si+Mn+Cr+Ni+Mo+Cu is 2.15~2.85.

[0430] Furthermore, the residual stress of the steel plate is ≤60MPa.

[0431] 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.

[0432] In this embodiment, the thickness d of the steel plate is ≥ 6 mm. For example, the thickness d is 6~100 mm.

[0433] In this embodiment, the steel plate exhibits excellent mechanical properties:

[0434] R m ≥570MPa;

[0435] R eL ≥460MPa;

[0436] A≥18%;

[0437] R eL / R m ≤0.85;

[0438] Z-direction reduction of area ≥45%.

[0439] The steel plate has excellent toughness:

[0440] Impact energy at 0℃ KV2≥330J;

[0441] Impact energy at -20℃ KV2≥320J;

[0442] -40℃ impact energy KV2≥300J;

[0443] -60℃ impact energy KV2≥280J;

[0444] ductile-brittle transition temperature T t50%US ≤-80℃;

[0445] At 0℃, the crack tip opening displacement of CTOD is ≥1.0mm;

[0446] At -20℃, the crack tip opening displacement of CTOD is ≥0.8mm;

[0447] At -40℃, the crack tip opening displacement of CTOD is ≥0.5mm.

[0448] In addition, the steel plate has excellent shape, with an unevenness of ≤2mm / m.

[0449] Furthermore, the microstructure of the steel plate is polygonal ferrite + acicular ferrite + tempered bainite + decomposed MA, and the total volume percentage of polygonal ferrite, acicular ferrite, tempered bainite and decomposed MA is 100%.

[0450] Among them, polygonal ferrite accounts for 25-35% of the volume, acicular ferrite accounts for 5-15% of the volume, tempered bainite accounts for 40-50% of the volume, and decomposed MA accounts for 10-20% of the volume.

[0451] The average grain size of the steel plate is 5~10μm.

[0452] In this embodiment, some parameters of the following processes differ from those in the first embodiment described above.

[0453] <Hot Rolling Process>

[0454] When the intermediate billet is cooled, the final cooling temperature A r3 +(40~60)℃.

[0455] During the second stage of rolling, the initial rolling temperature A r3 +(30~50)℃, final rolling temperature Ar3 +(-10~10)℃.

[0456] <Controlled Water Cooling Process>

[0457] Inlet water temperature A r3 -(40~20)℃, outlet water temperature B s -(50~10)℃.

[0458] <Tempering heat treatment process>

[0459] In this process, for the steel plate with a thickness d of 6~20mm, the tempering temperature T is B. s -(25~5)℃.

[0460] For the steel plate with a thickness d of 20~50mm, the tempering temperature T is B. s -(45~25)℃.

[0461] For the steel plate with a thickness d > 50 mm, the tempering temperature T is B. s -(65~45)℃.

[0462] The tempering and heat preservation time t1 is controlled according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥14.5, where t1 is in minutes.

[0463] The following are some experimental examples of this embodiment.

[0464] First, Table 16 shows the chemical composition of the steel plates in several test examples.

[0465] [Table 16]

[0466]

[0467] Each test case was prepared using the specific production method of this embodiment, and some parameters of each process are shown in Tables 17 and 18. " / " indicates that the corresponding process was not performed.

[0468] [Table 17]

[0469]

[0470] [Table 18]

[0471]

[0472] The microstructure and properties of the steel plates described in each test example were tested, and the results are shown in Tables 19 and 20. Additionally, Figure 4 The metallographic structure of Experimental Example 1C is shown.

[0473] [Table 19]

[0474]

[0475] [Table 20]

[0476]

[0477] Fifth Embodiment

[0478] This embodiment provides a bridge steel plate and its production method. Specifically, the steel plate is a Q500q grade or 500MPa grade bridge steel plate.

[0479] 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.

[0480] In this embodiment, the chemical composition of the steel plate, by mass percentage, includes: C 0.05~0.09%, Si 0.11~0.21%, Mn 1.17~1.25%, Cr 0.18~0.26%, Ni 0.22~0.30%, Mo 0.12~0.20%, Cu 0.22~0.30%, Nb 0.024~0.032%, Ti 0.010~0.018%, Al 0.024~0.048%, P 0.0080~0.0140%, S 0.0005~0.0030%, O 0.0011~0.0025%, N 0.0022~0.0048%, H 0.00005~0.00018%, with the remainder being iron and unavoidable impurities.

[0481] Furthermore, the chemical composition of the steel plate, by mass percentage, also satisfies the following: CEV is 0.334~0.430, Pcm is 0.144~0.206, Ni / Cu is 0.95~1.05, and 5C+Si+Mn+Cr+Ni+Mo+Cu is 2.27~2.97.

[0482] Furthermore, the residual stress of the steel plate is ≤70MPa.

[0483] 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.

[0484] In this embodiment, the thickness d of the steel plate is ≥ 6 mm. For example, the thickness d is 6~100 mm.

[0485] In this embodiment, the steel plate exhibits excellent mechanical properties:

[0486] R m ≥630MPa;

[0487] R eL ≥500MPa;

[0488] A≥18%;

[0489] R eL / R m ≤0.86;

[0490] Z-direction reduction of area ≥45%.

[0491] The steel plate has excellent toughness:

[0492] Impact energy at 0℃ KV2≥320J;

[0493] Impact energy at -20℃ KV2≥300J;

[0494] -40℃ impact energy KV2≥280J;

[0495] -60℃ impact energy KV2≥260J;

[0496] ductile-brittle transition temperature T t50%US ≤-80℃;

[0497] At 0℃, the crack tip opening displacement of CTOD is ≥1.0mm;

[0498] At -20℃, the crack tip opening displacement of CTOD is ≥0.8mm;

[0499] At -40℃, the crack tip opening displacement of CTOD is ≥0.5mm.

[0500] In addition, the steel plate has excellent shape, with an unevenness of ≤2mm / m.

[0501] Furthermore, the microstructure of the steel plate is polygonal ferrite + acicular ferrite + tempered bainite + decomposed MA, and the total volume percentage of polygonal ferrite, acicular ferrite, tempered bainite and decomposed MA is 100%.

[0502] Among them, polygonal ferrite accounts for 5-15% of the volume, acicular ferrite accounts for 10-20% of the volume, tempered bainite accounts for 45-55% of the volume, and decomposed MA accounts for 20-30% of the volume.

[0503] The average grain size of the steel plate is 4~9μm.

[0504] In this embodiment, some parameters of the following processes differ from those in the first embodiment described above.

[0505] <Hot Rolling Process>

[0506] When the intermediate billet is cooled, the final cooling temperature A r3 +(30~50)℃.

[0507] During the second stage of rolling, the initial rolling temperature A r3 +(20~40)℃, final rolling temperature A r3 -(20~0)℃.

[0508] <Controlled Water Cooling Process>

[0509] Inlet water temperature A r3 -(50~30)℃, outlet water temperature B s -(90~50)℃.

[0510] <Tempering heat treatment process>

[0511] In this process, for the steel plate with a thickness d of 6~20mm, the tempering temperature T is B. s -(45~25)℃.

[0512] For the steel plate with a thickness d of 20~50mm, the tempering temperature T is B. s -(65~45)℃.

[0513] For the steel plate with a thickness d > 50 mm, the tempering temperature T is B. s -(85~65)℃.

[0514] The tempering and heat preservation time t1 is controlled according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥14.1, where t1 is in minutes.

[0515] The following are some experimental examples of this embodiment.

[0516] First, Table 21 shows the chemical composition of the steel plates in several test examples.

[0517] [Table 21]

[0518]

[0519] Each test example was prepared using the specific production method of this first embodiment, and some parameters of each process are shown in Tables 22 and 23. " / " indicates that the corresponding process was not performed.

[0520] [Table 22]

[0521]

[0522] [Table 23]

[0523]

[0524] The microstructure and properties of the steel plates described in each test example were tested, and the results are shown in Tables 24 and 25. Additionally, Figure 5 The metallographic structure of Experimental Example 1D is shown.

[0525] [Table 24]

[0526]

[0527] [Table 25]

[0528]

[0529] Sixth Embodiment

[0530] This embodiment provides a bridge steel plate and its production method. Specifically, the steel plate is a Q550q grade or 550MPa grade bridge steel plate.

[0531] 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.

[0532] In this embodiment, the chemical composition of the steel plate, by mass percentage, includes: C 0.04~0.08%, Si 0.11~0.21%, Mn 1.22~1.30%, Cr 0.22~0.30%, Ni 0.22~0.30%, Mo 0.22~0.30%, Cu 0.22~0.30%, Nb 0.032~0.040%, Ti 0.010~0.018%, Al 0.024~0.048%, P 0.0060~0.0120%, S 0.0005~0.0020%, O 0.0011~0.0025%, N 0.0022~0.0048%, H 0.00005~0.00018%, with the remainder being iron and unavoidable impurities.

[0533] Furthermore, the chemical composition of the steel plate, by mass percentage, also satisfies the following: CEV 0.361~0.456, Pcm 0.145~0.207, Ni / Cu 0.95~1.05, Ni / Mo 0.95~1.05, Mo / Cu 0.95~1.05, and 5C+Si+Mn+Cr+Ni+Mo+Cu 2.41~3.11.

[0534] Furthermore, the residual stress of the steel plate is ≤80MPa.

[0535] 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.

[0536] In this embodiment, the thickness d of the steel plate is ≥ 6 mm. For example, the thickness d is 6~100 mm.

[0537] In this embodiment, the steel plate exhibits excellent mechanical properties:

[0538] R m ≥660MPa;

[0539] R eL ≥550MPa;

[0540] A≥16%;

[0541] R eL / R m ≤0.87;

[0542] Z-direction reduction of area ≥45%.

[0543] The steel plate has excellent toughness:

[0544] Impact energy at 0℃ KV2≥300J;

[0545] Impact energy at -20℃ KV2≥280J;

[0546] -40℃ impact energy KV2≥260J;

[0547] Impact energy at -60℃ KV2≥240J;

[0548] ductile-brittle transition temperature T t50%US ≤-80℃;

[0549] At 0℃, the crack tip opening displacement of CTOD is ≥1.0mm;

[0550] At -20℃, the crack tip opening displacement of CTOD is ≥0.8mm;

[0551] At -40℃, the crack tip opening displacement of CTOD is ≥0.5mm.

[0552] In addition, the steel plate has excellent shape, with an unevenness of ≤3mm / m.

[0553] Furthermore, the microstructure of the steel plate is polygonal ferrite + acicular ferrite + tempered bainite + decomposed MA, and the total volume percentage of polygonal ferrite, acicular ferrite, tempered bainite and decomposed MA is 100%.

[0554] Among them, polygonal ferrite accounts for 3~10% of the volume, acicular ferrite accounts for 12~25% of the volume, tempered bainite accounts for 50~60% of the volume, and decomposed MA accounts for 15~25% of the volume.

[0555] The average grain size of the steel plate is 3~8μm.

[0556] In this embodiment, some parameters of the following processes differ from those in the first embodiment described above.

[0557] <Hot Rolling Process>

[0558] When the intermediate billet is cooled, the final cooling temperature A r3 +(20~40)℃.

[0559] During the second stage of rolling, the initial rolling temperature A r3 +(10~30)℃, final rolling temperature A r3 -(30~10)℃.

[0560] <Controlled Water Cooling Process>

[0561] Inlet water temperature A r3 -(70~40)℃, outlet water temperature B s -(140~100)℃.

[0562] <Tempering heat treatment process>

[0563] In this process, for the steel plate with a thickness d of 6~20mm, the tempering temperature T is B. s -(65~45)℃.

[0564] For the steel plate with a thickness d of 20~50mm, the tempering temperature T is B. s -(85~65)℃.

[0565] For the steel plate with a thickness d > 50 mm, the tempering temperature T is B. s -(105~85)℃.

[0566] The tempering and heat preservation time t1 is controlled according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥13.7, where t1 is in minutes.

[0567] The following are some experimental examples of this embodiment.

[0568] First, Table 26 shows the chemical composition of the steel plates in several test examples.

[0569] [Table 26]

[0570]

[0571] Each test example was prepared using the specific production method of this first embodiment, and some parameters of each process are shown in Tables 27 and 28. " / " indicates that the corresponding process was not performed.

[0572] [Table 27]

[0573]

[0574] [Table 28]

[0575]

[0576] 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 6 The metallographic structure of Experimental Example 1E is shown.

[0577] [Table 29]

[0578]

[0579] [Table 30]

[0580]

Claims

1. A method for producing bridge steel plates, characterized in that, The chemical composition of the steel plate, by mass percentage, includes: C 0.04~0.13%, Si 0.11~0.21%, Mn 1.17~1.45%, Cr 0~0.30%, Ni 0.06~0.30%, Mo 0~0.30%, Cu 0~0.30%, Nb 0.012~0.040%, Ti 0.010~0.018%, Al 0.024~0.048%, P≤0.0200%, S≤0.0050%, O≤0.0025%, N≤0.0048%, H≤0.00018%, with the remainder being iron and unavoidable impurities; The production method includes sequential steps. Billet heating process: soaking temperature is T NbC +(100~150)℃, soaking time ≥25min; 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 +(60~100)℃, final rolling temperature T nr +(10~50)℃, the reduction in each pass is ≤30mm, and the reduction in the non-widening primary rolling pass is ≥20mm; during intermediate billet cooling, the intermediate billet thickness is 2.5~3.0 times the target thickness of the steel plate, and the final cooling temperature A r3 +(20~110)℃, cooling time ≥60s; during the second stage of rolling, the initial rolling temperature A r3 +(10~100)℃, final rolling temperature A r3 +(-30~60)℃, hold for 8~10s before the last rolling pass; Controlling the water cooling process: Inlet water temperature A r3 +(-70~30)℃, outlet water temperature B s +(-140~80)℃, cooling rate 8~20℃ / s; Tempering heat treatment process: The thickness d of the steel plate is 6~20mm, and the tempering temperature T is B. s +(-65~55)℃; or, the thickness d of the steel plate is 20~50mm, and the tempering temperature T is B. s +(-85~35)℃; or, if the thickness d of the steel plate is greater than 50mm, the tempering temperature T is B. s +(-105~15)℃; 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; 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. T NbC =7700 / (3.18-lg(Nb×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 =550-160C-10Mn-10Cr-10Ni-5Mo。 2. The method for producing bridge steel plates according to claim 1, characterized in that, Tempering heat treatment process: heating rate 8~15℃ / min.

3. The method for producing bridge steel plates according to claim 1, characterized in that, Tempering heat treatment process: Tempering heat treatment is carried out in a tempering furnace, which is maintained in a nitrogen atmosphere.

4. The method for producing bridge steel plates according to claim 1, characterized in that, The production method further includes a post-tempering stacking process following the tempering heat treatment process: after reaching the tempering holding time t1, 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℃.

5. The method for producing bridge steel plates according to claim 1, characterized in that, The production method also includes a surface treatment process between the controlled water cooling process and the tempering heat treatment process: after the steel plate is cooled to room temperature, the steel plate is surface treated by shot blasting or shot peening.

6. The method for producing bridge steel plates according to claim 5, characterized in that, Surface treatment process: The shot blasting or shot peening time t and the steel plate thickness d satisfy t=k×d+C, where t is in min, k is 0.1~0.2min / mm, and C is 5~7min.

7. The method for producing bridge steel plates according to claim 5, characterized in that, Surface treatment process: The shot blasting or shot peening rate P and the thickness d of the steel plate satisfy P=k1×d+C1, where the unit of P is kg / min, k1 is 0.4~0.6kg / (min·mm), and C1 is 160~200kg / min.

8. The method for producing bridge steel plates according to claim 5, characterized in that, Surface treatment process: The shot blasting or shot peening velocity S and the steel plate thickness d satisfy S=k2×d+C2, where S is in m / s, k2 is 0.1~0.3m / (s·mm), and C2 is 65~75m / s.

9. The method for producing bridge steel plates according to claim 1, characterized in that, The production method also includes an air cooling process between the water cooling process and the tempering heat treatment process: after the steel plate exits the water, it undergoes air cooling, with the upper cooling bed temperature B. s +(-150~200)℃, lower cooling bed temperature M s -(260~150)℃.

10. The method for producing bridge steel plates according to claim 1, characterized in that, The production method further includes a temperature-controlled preheating and straightening process between the hot rolling process and the controlled water cooling process: performing at least one preheating and straightening pass, with a straightening speed of 0.1~1.5 m / s and a straightening temperature A. r3 +(-65~25)℃, maximum reduction ≤4mm.

11. The method for producing bridge steel plates according to claim 1, characterized in that, During the second stage of rolling, the reduction in each pass is ≤20mm, and the reduction in the last pass is ≤3mm.

12. The method for producing bridge steel plates according to claim 1, characterized in that, The chemical composition of the steel plate, by mass percentage, also meets any one, two, three, or all of the following conditions: CEV = C + Mn / 6 + (Cr + Mo) / 5 + (Cu + Ni) / 15 is 0.239~0.532; Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15 is 0.103~0.265; The Ni / Cu ratio is 0.95~1.05; 5C+Si+Mn+Cr+Ni+Mo+Cu is 1.54~3.51; In the formula, the element symbols represent the mass percentage of the corresponding element.

13. The method for producing bridge steel plates according to claim 1, characterized in that, The billet heating process includes heat recovery, preheating, primary heating, secondary heating and homogenization. The heat recovery temperature is ≤850℃, the preheating temperature is ≤950℃, the primary heating temperature is 1020~1080℃, the secondary heating temperature is 1120~1180℃, and the total heating time is 0.019~0.023h / mm billet thickness.

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