Production method of carbon-manganese low-temperature steel medium plate

Abstract

The invention belongs to the technical field of metallurgy, and relates to a production method of a carbon-manganese low-temperature steel medium plate. The steel plate comprises the following chemical components in percentage by mass: 0.06 to 0.07 percent of C, 0.15 to 0.25 percent of Si, 1.40 to 1.50 percent of Mn, less than or equal to 0.012 percent of P, less than or equal to 0.003 percent of S, 0 to 0.15 percent of Ni, 0.010 to 0.015 percent of Nb, 0.008 to 0.018 percent of Ti, 0.020 to 0.050 percent of Al, less than or equal to 0.0070 percent of As and the balance of Fe and inevitable impurities. The method comprises the key production steps of converter smelting, LF refining, vacuum degassing, continuous casting, heating and rolling, wherein different rolling technologies are adopted according to the thicknesses of different finished products in the rolling stage, and meanwhile technological parameters such as rolling pass, speed control, descaling and rolled steel plate length are strictly controlled. According to the invention, the impact performance stability in the batch production process is obviously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy, and particularly relates to a production method for medium and heavy plates of carbon manganese low-temperature steel. Background Art

[0002] Carbon manganese low-temperature steel is a kind of steel material with excellent properties, mainly used for manufacturing transport ships such as liquefied petroleum gas and liquid ammonia carriers. In recent years, with the rapid development of offshore energy transportation, the order volume of LPG ships / VLGC ships in China has increased rapidly, and carbon manganese low-temperature steel has also been continuously improved and iterated.

[0003] Patent CN119411008A introduces a low yield ratio low-temperature steel and its production method. The mass percentage of chemical components is: C: 0.07% - 0.08%, Si: 0.15% - 0.25%, Mn: 1.30% - 1.40%, P ≤ 0.012%, S ≤ 0.003%, Ni: 0.10% - 0.20%, Nb: 0.012% - 0.017%, Ti: 0.008% - 0.020%, Al: 0.020% - 0.050%, and the rest is Fe and inevitable impurities. The involved specifications are 8 - 30 mm. However, in production practice, it is found that the impact performance of the produced thin-specification steel plates fluctuates, especially for the specifications below 12 mm. The present invention has taken a series of targeted improvements, and the verification measures are effective, and the performance stability has been significantly improved. Summary of the Invention

[0004] The problem to be solved by the present invention is to effectively improve the performance stability of large-scale production of carbon manganese low-temperature steel. A carbon manganese low-temperature steel plate and its production method are provided. The thickness specification of the produced steel plate is 6 - 40 mm, the yield strength is 355 - 440 MPa, the tensile strength is 470 - 520 MPa, the elongation is ≥ 30%, the yield ratio is ≤ 0.90, and the impact energy Akv at -60 °C is ≥ 100 J.

[0005] The technical solution adopted by the present invention is: a production method for medium and heavy plates of carbon manganese low-temperature steel. The mass percentage of the chemical components of the steel is: C: 0.06% - 0.07%, Si: 0.15% - 0.25%, Mn: 1.35% - 1.45%, P ≤ 0.012%, S ≤ 0.003%, Ni: 0% - 0.15%, Nb: 0.010% - 0.015%, Ti: 0.008% - 0.018%, Al: 0.020% - 0.050%, As ≤ 0.0070%, and the rest is Fe and inevitable impurities;

[0006] The production method includes: step (1) converter smelting, step (2) LF refining, step (3) vacuum degassing, step (4) continuous casting, step (5) heating, and step (6) rolling; the thickness specification of the rolled steel plate is 6 - 40 mm, and the delivery condition is TMCP.

[0007] Among them, in the step (6) rolling, different rolling processes are adopted according to different finished product thicknesses in the rolling stage, and at the same time, process parameters such as rolling passes, speed control, descaling, and the length of the rolled steel plate are strictly controlled.

[0008] For steel plates with a thickness of 6 - 12 mm, the thickness of the intermediate billet is not less than 65 mm, the final rolling temperature of the steel plate is 830 - 850 °C, weak cooling is carried out after rolling, and the recrystallization temperature is 730 - 740 °C.

[0009] For steel plates with a thickness of 12.5 - 18 mm, the thickness of the intermediate billet is not less than 75 mm, the final rolling temperature of the steel plate is 810 - 830 °C, weak cooling is carried out after rolling, and the recrystallization temperature is 700 - 720 °C.

[0010] For steel plates with a thickness of 20 - 40 mm, the thickness of the intermediate billet is not less than 75 mm, the final rolling temperature of the steel plate is 800 - 820 °C, weak cooling is carried out after rolling, and the recrystallization temperature is 670 - 690 °C.

[0011] Furthermore, the step (1) converter smelting is as follows: smelting is carried out in a combined blowing converter using blast furnace hot metal + scrap steel, controlling the tapping temperature at 1580 - 1620 °C, P ≤ 0.008% in the converter tapping, adding deoxidizers and silicomanganese alloy for deoxidation and alloying during tapping, and the As content in the blast furnace hot metal ≤ 0.007%.

[0012] Furthermore, the step (2) LF refining is as follows: the ladle molten steel is powered on in the LF furnace, slag is formed for temperature adjustment, and low-carbon ferromanganese, ferroniobium, ferronickel, and ferro-titanium are added for precise adjustment of chemical composition.

[0013] Furthermore, the step (3) vacuum degassing is as follows: the ladle molten steel is sent into the VD furnace for vacuum treatment, calcium treatment is carried out after the vacuum treatment is completed, and finally bottom blowing argon gas is used for steel liquid calming treatment. After vacuum degassing, the gas content H ≤ 0.00015%, N ≤ 0.0040%, and O ≤ 0.0010%.

[0014] Furthermore, the step (4) continuous casting is as follows: the superheat of the tundish is 12 - 25 °C, and soft reduction is adopted in continuous casting to improve the internal quality of the continuous casting billet. The cumulative reduction at the solidification end of continuous casting is 8 - 12 mm, and the thickness dimension of the continuous casting billet is 180 - 260 mm, and the width dimension is 1500 - 2300 mm.

[0015] Further, the heating in step (5) is as follows: the temperature of the preheating section is 650 - 900°C, the temperature of the heating section is 1050 - 1220°C, the temperature of the soaking section is 1130 - 1220°C, and the discharging temperature is 1150 - 1220°C.

[0016] Further, in step (6), the finish rolling of the steel plate also includes controlling the finish rolling passes of the steel plate to be 7 - 9 passes, the biting and throwing speeds of the finish rolling being ≥2 m / s, the throwing distance being ≥3 m, the maximum speed of the last pass of rolling being 4 - 6 m / s, descaling in the first and second passes of the finish rolling, and the total rolling length of the steel plate being not greater than 45 m.

[0017] Further, for a slab with a thickness of 180 - 210 mm, the furnace temperature is not greater than 1200°C, and the discharging temperature is 1150 - 1200°C; for a slab with a thickness of 220 - 260 mm, the furnace temperature is not greater than 1220°C, and the discharging temperature is 1150 - 1220°C.

[0018] The functions of the various elements in the present invention are as follows:

[0019] Carbon (C): Carbon exists in the steel in the form of interstitial solid solution and can also form carbides with other elements. Carbon can effectively improve the strength of the steel. The change in the carbon content in the steel will change the content of ferrite and pearlite in the steel and affect the toughness and welding and other process properties of the steel.

[0020] Silicon (Si): Silicon is one of the deoxidizing elements in the steelmaking process. When it exists in the steel as a solid solution element, it can significantly improve the strength of the steel grade; silicon also has various effects on the carbides in the steel. It can not only change the type and morphology of the carbides, promote the decomposition and refinement of the carbides, but also affect the transformation and distribution of the carbides to a certain extent.

[0021] Manganese (Mn): Manganese is one of the main alloying elements in the steel. It can improve the strength through solid solution strengthening. Manganese can lower the critical transformation temperature to refine pearlite and indirectly improve the strength of the steel. Manganese can eliminate or weaken the hot brittleness of the steel caused by sulfur. Manganese can improve the low-temperature impact toughness of the steel. Manganese is a carbide-forming element and affects the microstructure and properties of the steel.

[0022] Nickel (Ni): Nickel can be infinitely soluble in iron, expand the austenite phase region, and is beneficial to the formation and stabilization of austenite; nickel can strengthen ferrite by solid solution strengthening and refine and increase pearlite; nickel can improve the low-temperature toughness of the steel; nickel can improve the weldability of the steel, reduce the precipitation of intermetallic compounds, and prevent and reduce their harmful effects; nickel can increase the stacking fault energy of the steel and increase the mobile dislocations during the deformation process, thereby improving the plasticity and toughness of the steel.

[0023] Niobium (Nb): As a microalloying element, a small addition of niobium will have a great impact on the properties of steel. Niobium can effectively refine the austenite grains during heating and rolling processes, inhibit austenite recrystallization. The precipitates of niobium can improve the mechanical properties of steel. Niobium can reduce the lamellar spacing of pearlite, reduce polygonal ferrite, refine the microstructure and improve the impact toughness; niobium has a significant impact on the yield strength of steel.

[0024] Titanium (Ti): Titanium is an alloying element. Titanium has a very strong affinity with nitrogen and carbon, which is beneficial to controlling the surface quality of slab; Titanium can inhibit the growth of austenite grains during heating process, and is beneficial to refining austenite grains during heating and rolling processes. The precipitates of titanium can improve the mechanical properties of steel, and titanium can also improve the toughness of steel at low temperatures.

[0025] Aluminum (Al): Aluminum is a strong deoxidizer, mainly added to molten steel as a deoxidizing alloy in molten steel. At the same time, Al has a strong affinity with N, which can inhibit the harm of nitrogen in steel; Al can refine the microstructure of steel, thereby improving the strength and toughness of steel.

[0026] Phosphorus (P): Phosphorus is a harmful element in steel, which will reduce the plasticity and toughness of steel, especially causing great damage to toughness at low temperature states. Phosphorus will also deteriorate the welding performance of steel.

[0027] Sulfur (S): Sulfur is a harmful element in steel. It will cause hot brittleness of steel at high temperatures, reduce the plasticity and toughness of steel, and cause internal cracks in steel. The formation of manganese sulfide by sulfur and manganese in steel will affect the uniformity of steel and have an adverse impact on performance.

[0028] Arsenic (As): Arsenic is a harmful impurity element. It is usually brought in from blast furnace hot metal or scrap steel, but it is not easy to remove during the steelmaking process. Previous studies have pointed out that As exceeding 0.05% will be harmful to low-temperature impact, and there are few reports or studies on the impact of ultra-low temperature impact at -60°C and below.

[0029] Principle of the present invention: The carbon manganese low-temperature steel plate of the present invention has a thickness specification of 6 - 40 mm and a delivery condition of TMCP. The microstructure type is designed as polygonal ferrite + pearlite. The chemical element control of the present invention adopts narrow composition range control. Vacuum treatment + calcium treatment + deoxidation treatment are carried out during the smelting process to reduce inclusions in molten steel. Low superheat + reduction at the end of solidification are adopted during the continuous casting process to improve the density of the slab and reduce segregation. Different heating systems are adopted for billets with different thicknesses during the slab heating process. Different rolling processes are adopted according to different finished product thicknesses during the rolling stage. At the same time, process parameters such as rolling passes, speed control, descaling, and the length of the rolled steel plate are strictly controlled to achieve the best organizational performance within the full size range of the final finished steel plate, and at the same time ensure the performance qualification rate of batch production of steel plates.

[0030] The beneficial effects of the present invention are as follows: The carbon manganese low-temperature steel plate of the present invention significantly improves the impact performance stability during mass production by controlling the narrow composition and refining the process control parameters during the heating and rolling process, and can further reduce the Ni content to achieve cost reduction. Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0032] Figure 1 It is the metallographic structure diagram of the present invention. Detailed Embodiments

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0034] The R & D motivation of the present invention: Patent CN119411008A introduces a low yield ratio low-temperature steel and its production method. The mass percentage of chemical components is: C: 0.07% - 0.08%, Si: 0.15% - 0.25%, Mn: 1.30% - 1.40%, P ≤ 0.012%, S ≤ 0.003%, Ni: 0.10% - 0.20%, Nb: 0.012% - 0.017%, Ti: 0.008% - 0.020%, Al: 0.020% - 0.050%, and the rest are Fe and inevitable impurities. It is found in mass production that the problem of performance qualification rate is relatively prominent, mainly manifested as large fluctuations in impact performance. For example, in the 97 batches produced in October 2024, 6 batches had a yield strength exceeding 440 MPa, 3 batches had a yield ratio exceeding 0.90, 11 batches had an impact below 80 J, and the total number of unqualified batches was 15, with a qualification rate of 84.5%. The process capability CPK of the yield strength in this batch of production is 0.97, the process capability CPK of the yield ratio is 1.12, and the process capability CPK of the -60°C impact energy is 0.67.

[0035] To solve this problem, optimization in the rolling process was carried out based on experience. The finishing rolling temperature was controlled at the lower limit of 810 - 830 °C (i.e., around 810 °C), and the thickness of the intermediate billet was reduced to avoid uneven austenite grain caused by inappropriate reduction ratio in the early stage of the finishing rolling stage, which could reduce the impact performance. In November 2024, 73 batches were produced. Among them, 3 batches had a yield strength exceeding 440 MPa, and another 3 batches had an impact energy at -60 °C lower than 80 J. The total number of unqualified batches was 6, and the qualified rate increased to 91.7%. The process capability CPK of the yield strength of this batch of production was 0.95, the process capability CPK of the yield ratio was 0.78, and the process capability CPK of the impact energy at -60 °C was 1.38.

[0036] In December 2024, large-scale production started according to the adjusted process, and significant fluctuations in performance occurred. A total of 305 batches were produced in December. Among them, 14 batches had a yield strength exceeding 440 MPa, 2 batches had a yield ratio exceeding 0.90, and 71 batches had an impact energy at -60 °C lower than 80 J. The total number of unqualified batches was 81, and the qualified rate increased to 73.4%. The process capability CPK of the yield strength of the steel in this batch of production was 0.79, the process capability CPK of the yield ratio was 0.86, and the process capability CPK of the impact energy at -60 °C was 0.54. In 2025, some customers put forward higher requirements for the impact energy, and the order thickness was 6 - 40 mm, and the maximum width reached 4500 mm. Considering comprehensively, it was decided to redesign the composition and process. The first trial production was carried out in January, and the trial production composition is shown in Table 1:

[0037] Table 1: Composition of the steel in the first trial production by mass percentage

[0038] C Si Mn P S Al Nb Ti Ni 0.05 0.18 1.20 0.008 0.0023 0.030 0.012 0.01 0.11

[0039] The tapping temperature was 1170 - 1220 °C, the intermediate billet was 60 - 70 mm, the finishing rolling temperature was 810 - 850 °C, the trial production specification was 8 - 12 mm, and the performance is shown in Table 2:

[0040] Table 2: Performance of the steel in the first trial production

[0041] Specification Yield Tensile Elongation Yield ratio Transverse impact Longitudinal impact 8*4000 399 474 42 0.84 126、123、118 123、127、129 10*4500 380 455 38 0.84 333、327、337 322、319、330 10*4500 385 450 39 0.86 329、346、349 334、332、343 12*2200 376 436 45 0.86 326、334、335 328、323、309 12*2200 395 448 43 0.88 324、330、331 332、309、326

[0042] It can be seen from the table that although the impact performance was good, the tensile strength was lower than the lower limit of 440 MPa. The chemical composition was adjusted and the second trial production was carried out. The composition is shown in Table 3.

[0043] Table 3: Composition of the steel in the second trial production by mass percentage

[0044]

[0045] The main rolling process of the second trial production is as follows:

[0046] 8*3000 batches: furnace temperature 1179℃, intermediate billet 75mm, final rolling temperature 836℃, no water cooling.

[0047] 8*2500 batches: furnace temperature 1180℃, intermediate billet 70mm, final rolling temperature 844℃, no water cooling.

[0048] 12*2500 batches: furnace temperature 1187℃, intermediate billet 75mm, final rolling temperature 821℃, no water cooling.

[0049] Batch 16*1700: furnace temperature 1188℃, intermediate billet 75mm, final rolling temperature 814℃, and red-returning temperature 720℃.

[0050] 30*2300 batches: furnace temperature 1191℃, intermediate billet 75mm, final rolling temperature 810℃, red-returning temperature 695℃.

[0051] The performance of the second trial production is as follows:

[0052] Table 4: Performance of the second trial steel

[0053]

[0054] The subsequent batch production will be arranged with a qualified rate of about 92%. After increasing the cutting amount of the head and tail of the steel plate and optimizing the rolling process of different specifications, the performance qualified rate will be further improved to about 96%. In order to ensure the performance qualified rate and reduce the loss of yield rate, the process parameters of the finishing rolling mill are adjusted (mainly the steel biting speed, steel throwing distance, rolling speed, etc.). At the same time, in order to ensure the uniformity of the performance of the steel plate over the entire length range, the total length of the steel plate rolling is limited. The production qualified rate in February 2025 is between 95% and 97%.

[0055] Based on the above experiments, the present invention provides a method for producing a carbon-manganese low-temperature steel medium and thick plate, comprising: step (1) converter smelting, step (2) LF refining, step (3) vacuum degassing, step (4) continuous casting, step (5) heating, and step (6) rolling; wherein the chemical composition mass percentage of the steel is: C: 0.06% to 0.07%, Si: 0.15% to 0.25%, Mn: 1.35% to 1.45%, P≤0.012%, S≤0.003%, Ni: 0% to 0.15%, Nb: 0.010% to 0.015%, Ti: 0.008% to 0.018%, Al: 0.020% to 0.050%, As≤0.0070%, and the rest is Fe and unavoidable impurities;

[0056] Step (1) Converter smelting: The converter smelting is carried out by using blast furnace hot metal + scrap steel, with a top and bottom combined blown converter. The tapping temperature is controlled at 1580 - 1620°C. The P content in the converter tapping is ≤0.008%. During the tapping process, deoxidizers and ferrosilicon manganese alloy are added for deoxidation and alloying. The As content in the blast furnace hot metal is ≤0.007%.

[0057] Step (2) LF refining: The ladle molten steel is charged into the LF furnace for power supply, slag making and temperature adjustment, and low-carbon ferromanganese, ferro-niobium, ferro-nickel, and ferro-titanium are added for precise adjustment of chemical composition.

[0058] Step (3) Vacuum degassing: The ladle molten steel is sent into the VD furnace for vacuum treatment. After the vacuum treatment, calcium treatment is carried out, and finally, bottom blowing argon gas is used for steel water calming treatment. The gas content after vacuum degassing is H ≤ 0.00015%, N ≤ 0.0040%, and O ≤ 0.0010%.

[0059] Step (4) Continuous casting: The superheat of the tundish is 12 - 25°C. Soft reduction is adopted in continuous casting to improve the internal quality of the continuous casting billet. The cumulative reduction at the solidification end of continuous casting is 8 - 12 mm. The thickness dimension of the continuous casting billet is 180 - 260 mm, and the width dimension is 1500 - 2300 mm.

[0060] Step (5) Heating: The temperature of the preheating section is 650 - 900°C, the temperature of the heating section is 1050 - 1220°C, the temperature of the soaking section is 1130 - 1220°C, and the tapping temperature is 1150 - 1220°C;

[0061] Among them, for the slab with a thickness of 180 - 210 mm, the furnace temperature is not greater than 1200°C, and the tapping temperature is 1150 - 1200°C; for the slab with a thickness of 220 - 260 mm, the furnace temperature is not greater than 1220°C, and the tapping temperature is 1150 - 1220°C.

[0062] Step (6) Rolling: In the rolling stage, different rolling processes are adopted according to different finished product thicknesses. At the same time, the process parameters such as rolling passes, speed control, descaling, and the length of the rolled steel plate are strictly controlled;

[0063] Among them, for the steel plate with a thickness of 6 - 12 mm, the thickness of the intermediate billet is not less than 65 mm, the finish rolling temperature of the steel plate is 830 - 850°C, and it is weakly cooled after rolling, and the recrystallization temperature is 730 - 740°C; for the steel plate with a thickness of 12.5 - 18 mm, the thickness of the intermediate billet is not less than 75 mm, the finish rolling temperature of the steel plate is 810 - 830°C, and it is weakly cooled after rolling, and the recrystallization temperature is 700 - 720°C; for the steel plate with a thickness of 20 - 40 mm, the thickness of the intermediate billet is not less than 75 mm, the finish rolling temperature of the steel plate is 800 - 820°C, and it is weakly cooled after rolling, and the recrystallization temperature is 670 - 690°C. The finish rolling passes of the steel plate are controlled within 7 - 9 passes. The biting and throwing speeds in finish rolling are ≥2 m / s, the throwing distance is ≥3 m, the maximum speed in the last pass of rolling is 4 - 6 m / s, descaling is carried out in the first and second passes of finish rolling, and the total length of the steel plate rolling is not greater than 45 m.

[0064] The production method of the medium and heavy plate of carbon manganese low-temperature steel of the present invention will be described in detail below in conjunction with specific embodiments.

[0065] Example 1:

[0066] The chemical composition of the low-alloy structural heavy plate in this example is as follows by mass percentage: C: 0.07%, Si: 0.17%, Mn: 1.36%, P: 0.012%, S: 0.0018%, Ni: 0.11%, Nb: 0.012%, Ti: 0.014%, Al: 0.040%, As: 0.0058%, and the rest is Fe and inevitable impurities.

[0067] The specific production method steps are as follows:

[0068] (1) Converter smelting: The As content of the hot metal entering the furnace is 0.0062%. Appropriate scrap steel is added, and the converter is blown with oxygen for smelting. The tapping temperature of the converter is 1584°C. During tapping, aluminum blocks and silicomanganese are added for deoxidation, and ferrosilicon, silicomanganese, and low-carbon ferromanganese are added for alloying.

[0069] (2) Refining: After the ladle molten steel is heated up by power supply in the LF furnace, ferroniobium, ferronickel, and ferro-titanium are added for precise adjustment of the chemical composition. After LF refining is completed, it is sent to the RH station.

[0070] (3) Vacuum treatment: Vacuum treatment is carried out in the RH furnace. After vacuum treatment, a calcium wire is fed, and the molten steel is allowed to stand for 15 minutes.

[0071] (4) Continuous casting: The superheat of the tundish is 22 - 25°C. Soft reduction is used to improve the internal density of the slab and reduce internal segregation. The thickness dimension of the continuous casting billet is 180 mm.

[0072] (5) Heating: The slab is heated in a walking beam continuous reheating furnace. The maximum furnace temperature is 1200°C, and the tapping temperature is 1170 - 1200°C.

[0073] (6) Rolling: Two-stage controlled rolling is adopted. The finished product specification is 10 - 20 mm. The rolling temperature in the rough rolling is 1100 - 1040°C, the thickness of the intermediate slab is 70 - 75 mm, the starting rolling temperature in the finish rolling is 980 - 1020°C, the final rolling temperature in the finish rolling is 810 - 840°C; the recrystallization temperature is 700 - 740°C.

[0074] Example 2:

[0075] The chemical composition mass percentages of the low-alloy structural heavy plate described in this embodiment are as follows: C: 0.06%, Si: 0.16%, Mn: 1.44%, P: 0.008%, S: 0.0015%, Ni: 0.03%, Nb: 0.013%, Ti: 0.011%, Al: 0.028%, As: 0.0043%, and the balance is Fe and unavoidable impurities.

[0076] The specific production method steps are as follows:

[0077] (1) Converter smelting: The As content of the hot metal charged into the furnace is 0.0062%. Appropriate scrap steel is added, and the converter is blown with oxygen for smelting. The tapping temperature of the converter is 1602°C. Aluminum blocks and silicomanganese are added for deoxidation during tapping, and ferrosilicon, silicomanganese, and low-carbon ferromanganese are added for alloying.

[0078] (2) Refining: After the ladle molten steel is heated by power supply in the LF furnace, ferroniobium, ferronickel, and ferrotitanium are added for precise adjustment of the chemical composition. After the LF refining is completed, it is sent to the RH station.

[0079] (3) Vacuum treatment: Vacuum treatment is carried out in the RH furnace. After the vacuum treatment, a calcium wire is fed, and the molten steel is allowed to stand for 15 min.

[0080] (4) Continuous casting: The superheat of the tundish is 15 - 21°C. Soft reduction is used to improve the internal density of the slab and reduce internal segregation. The thickness dimension of the continuous casting billet is 260 mm.

[0081] (5) Heating: The slab is heated in a walking beam continuous reheating furnace. The maximum furnace temperature is 1220°C, and the tapping temperature is 1150 - 1170°C.

[0082] (6) Rolling: Two-stage controlled rolling is adopted. The finished product specifications are 22 - 40 mm. The rolling temperature in the rough rolling is 1050 - 1000°C, the thickness of the intermediate billet is 75 mm, the rolling start temperature in the finish rolling is 980 - 1020°C, the finish rolling temperature in the finish rolling is 800 - 820°C; the recrystallization temperature is 680 - 710°C.

[0083] Comparative Example 1:

[0084] The chemical composition mass percentages of the low-alloy structural heavy plate described in this embodiment are as follows: C: 0.07%, Si: 0.24%, Mn: 1.34%, P: 0.010%, S: 0.0014%, Ni: 0.11%, Nb: 0.014%, Ti: 0.016%, Al: 0.023%, As: 0.0101%, and the balance is Fe and unavoidable impurities.

[0085] The specific production method steps are as follows:

[0086] (1) Converter smelting: The As content in the hot metal charged into the furnace is 0.0105%. Appropriate scrap steel is added, and the converter is blown with oxygen for smelting. The tapping temperature of the converter is 1612°C. During tapping, aluminum blocks and silicomanganese are added for deoxidation, and ferrosilicon, silicomanganese, and low-carbon ferromanganese are added for alloying.

[0087] (2) Refining: After the molten steel in the tundish is heated up by power supply in the LF furnace, ferroniobium, ferronickel, and ferro-titanium are added for precise adjustment of chemical composition. After LF refining is completed, it is sent to the RH station.

[0088] (3) Vacuum treatment: Vacuum treatment is carried out in the RH furnace. After vacuum treatment, a calcium wire is fed, and the molten steel is left standing for 15 minutes.

[0089] (4) Continuous casting: The superheat of the tundish is 16 - 22°C. Soft reduction is adopted to improve the internal density of the slab and reduce internal segregation. The thickness dimension of the continuous casting slab is 220 mm.

[0090] (5) Heating: The slab is heated in a walking beam continuous reheating furnace. The maximum furnace temperature is 1220°C, and the tapping temperature is 1170 - 1205°C.

[0091] (6) Rolling: Two-stage controlled rolling is adopted. The finished product specifications are 8 - 20 mm. The rolling temperature in the roughing stage is 1150 - 1080°C, the thickness of the intermediate billet is 75 - 90 mm, the rolling start temperature in the finishing stage is 980 - 1020°C, the final rolling temperature in the finishing stage is 814 - 832°C; the recrystallization temperature is 685 - 725°C.

[0092] Table 5 Mechanical properties of the examples and comparative examples

[0093]

[0094]

[0095]

[0096]

[0097] It can be seen from the above data that the impact performance of the comparative example that does not adopt the technical solution of the present invention is unstable, and the impact energy (J) at -60°C is high and low, while for the examples that adopt the technical solution of the present invention, the impact performance is stable during mass production.

[0098] The above are only the preferred embodiments of the present invention, and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are all included within the protection scope of the present invention.

Claims

1. A production method of medium and heavy plates of carbon manganese low-temperature steel, characterized in that, The chemical composition of the steel by mass percentage is as follows: C: 0.06% - 0.07%, Si: 0.15% - 0.25%, Mn: 1.35% - 1.45%, P ≤ 0.012%, S ≤ 0.003%, Ni: 0% - 0.15%, Nb: 0.010% - 0.015%, Ti: 0.008% - 0.018%, Al: 0.020% - 0.050%, As ≤ 0.0070%, and the rest is Fe and inevitable impurities; The production method includes: step (1) converter smelting, step (2) LF refining, step (3) vacuum degassing, step (4) continuous casting, step (5) heating, and step (6) rolling; the thickness specification of the rolled steel plate is 6 - 40 mm, and the delivery condition is TMCP; Among them, in the said step (6) rolling, different rolling processes are adopted according to different finished product thicknesses in the rolling stage, and at the same time, strict control is carried out on process parameters such as rolling passes, speed control, descaling, and the length of the rolled steel plate; For steel plates with a thickness of 6 - 12 mm, the thickness of the intermediate billet is not less than 65 mm, the finish rolling temperature of the steel plate is 830 - 850 °C, weakly cooled after rolling, and the recrystallization temperature is 730 - 740 °C; For steel plates with a thickness of 12.5 - 18 mm, the thickness of the intermediate billet is not less than 75 mm, the finish rolling temperature of the steel plate is 810 - 830 °C, weakly cooled after rolling, and the recrystallization temperature is 700 - 720 °C; For steel plates with a thickness of 20 - 40 mm, the thickness of the intermediate billet is not less than 75 mm, the finish rolling temperature of the steel plate is 800 - 820 °C, weakly cooled after rolling, and the recrystallization temperature is 670 - 690 °C.

2. The production method of a medium and heavy plate of carbon manganese low-temperature steel according to claim 1, characterized in that, The said step (1) converter smelting is as follows: smelting is carried out in the way of blast furnace hot metal + scrap steel, a top-bottom combined blown converter, controlling the tapping temperature at 1580 - 1620 °C, P ≤ 0.008% in the converter tapping, adding deoxidizer and silicomanganese alloy for deoxidation alloying during the tapping process, and the As content in the blast furnace hot metal ≤ 0.007%.

3. The production method of a medium and heavy plate of carbon manganese low-temperature steel according to claim 1, characterized in that, The said step (2) LF refining is as follows: the ladle molten steel is powered on in the LF furnace, slag is made and the temperature is adjusted, and low-carbon ferromanganese, ferroniobium, ferronickel, and ferro-titanium are added for precise adjustment of chemical composition.

4. The production method of a medium and heavy plate of carbon manganese low-temperature steel according to claim 1, characterized in that, The said step (3) vacuum degassing is as follows: the ladle molten steel is sent into the VD furnace for vacuum treatment, calcium treatment is carried out after the vacuum treatment is completed, and finally bottom blowing argon gas for steel water calming treatment is carried out. After vacuum degassing, the gas content is H ≤ 0.00015%, N ≤ 0.0040%, and O ≤ 0.0010%.

5. The production method of a medium-thick plate of carbon manganese low-temperature steel according to claim 1, characterized in that, The said step (4) continuous casting is as follows: the superheat of the tundish is 12 - 25 °C, soft reduction is adopted in continuous casting to improve the internal quality of the continuous casting billet, the cumulative reduction at the solidification end of continuous casting is 8 - 12 mm, and the thickness dimension of the continuous casting billet is 180 - 260 mm and the width dimension is 1500 - 2300 mm.

6. The production method of a medium and heavy plate of carbon manganese low-temperature steel according to claim 1, characterized in that, The said step (5) heating is as follows: the temperature of the preheating section is 650 - 900 °C, the temperature of the heating section is 1050 - 1220 °C, the temperature of the soaking section is 1130 - 1220 °C, and the furnace outlet temperature is 1150 - 1220 °C.

7. The production method of a medium and heavy plate of carbon manganese low-temperature steel according to claim 1, characterized in that, The rolling in step (6) further includes that the finish rolling passes of the steel plate are controlled at 7 to 9 passes, the biting and throwing speeds of finish rolling are ≥ 2 m / s, the throwing distance is ≥ 3 m, the maximum speed of the last pass of rolling is 4 to 6 m / s, descaling is carried out in the first and second passes of finish rolling, and the total rolling length of the steel plate is not more than 45 m.

8. The production method of a medium and heavy plate of carbon manganese low-temperature steel according to claim 6, characterized in that, For slab with a thickness of 180 - 210 mm, the furnace temperature is not more than 1200 °C, and the tapping temperature is 1150 - 1200 °C; for slab with a thickness of 220 - 260 mm, the furnace temperature is not more than 1220 °C, and the tapping temperature is 1150 - 1220 °C.

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