High hardness die steel plate having anti-hic and ssc dual resistance performance and manufacturing method

Abstract

The present application relates to a kind of high-hardness die steel plate with anti-HIC and SSCC dual resistance performance and manufacturing method, the chemical composition of the steel plate is as follows in percentage by mass C 0.30~0.50%, Si 0.20~0.50%; P≤0.005%; S≤0.002%; Mn 0.50~0.80%; Al 0.02~0.04%; Nb≤0.01%; V≤0.01%; Cr0.35~0.75%; Mo+Ni+Cu 0.15~0.25%; Ceq≤0.80;The balance is Fe and inevitable impurities.The manufacturing process is KR molten iron pretreatment-BOF smelting-LF and RH furnace refining-continuous casting of slab-hot delivery hot charging-slab heating-quick TMCP rolling-high temperature DQ cooling-straightening-cold bed cooling-steel plate shearing and other processes.The present application is designed to use medium C, Cr and micro-alloy composite addition+quick TMCP+high temperature DQ process to produce 8~90mm thickness steel plate, through specific process parameters and corresponding regression equation, the use of the process and regression equation can produce unique microstructure;Make the steel plate can satisfy the dual resistance performance of steel plate, while having Vickers hardness≥400HV10, and the use requirement of die steel under acidic service condition.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of special steel smelting, and particularly relates to a high-hardness die steel plate with anti-HIC and SSCC dual resistance and a manufacturing method. BACKGROUND

[0002] In recent years, with the shift of global manufacturing centers to China and Southeast Asia, and the fact that China has become a world manufacturing center and manufacturing power, the development of manufacturing industry has greatly promoted the development of die steel industry. At present, the die market sales in China have exceeded 3 million tons, and the sales have exceeded 400 billion RMB. Although the demand for dies in China has increased sharply, the self-provision rate of domestic dies is insufficient, and there is an oversupply of low-grade dies, while high-grade die steels mainly rely on imports, especially acid-resistant, corrosion-resistant, high-hardness, large-scale, precise, long-life die steels. With the rapid development of new energy automobile industry, high-quality rubber and high-hardness plastic die industry, many industrialized countries are now researching acid-resistant, high-hardness and low-cost die steels. At present, the research on acid resistance and high hardness of low-cost die steels in industrialized countries is still in the exploratory stage.

[0003] According to the characteristics of high-hardness die steels with anti-HIC and SSCC dual resistance, and combined with customer demand, this paper proposes a high-hardness die steel plate with anti-HIC and SSCC dual resistance and a manufacturing method.

[0004] This patent first proposes a high-hardness die steel plate with anti-HIC and SSCC dual resistance, and systematically studies the chemical composition, production process, acid resistance, high hardness and microstructure performance of acid-resistant and high-hardness die steels. This patent uses medium C, Cr and micro-alloy composite addition + rapid TMCP + high temperature DQ process to produce 8-90mm thick steel plates. Through specific process parameters and corresponding high-hardness performance, a specific regression equation is found. The use of this process and regression equation can produce a mixed microstructure composed of martensite + bainite + long acicular ferrite. The steel plate with this unique microstructure can meet the dual resistance of the steel plate, and also has a Vickers hardness of ≥400HV10 and the use requirements of die steels under acid service conditions.

[0005] The previous patent publication No. CN102605264A proposes a preparation method of an ultra-high toughness high-hardness corrosion-resistant die steel, which is different from the present patent in the following aspects: CN102605264A adopts high C+high Cr+high Co+high Mo+V+Ti and rare earth RE composition design, and the process adopts electroslag remelting and quenching+tempering, while the present patent adopts medium C+low Cr+(Mo+Ni+Cu) composite addition, and the process adopts slab continuous casting and rapid TMCP+online high-temperature DQ cooling; on the other hand, the applications are different, CN102605264A is applied to flat steel and corrosion-resistant die steel, and the present patent is suitable for die industry in S-containing and high-temperature H2O steam and other acidic environments. Another patent publication No. CN113584379A proposes a low-carbon high-hardness high-toughness combined die steel and its production process, which is different from the present patent in the following aspects: one aspect is the chemical composition, CN113584379A adopts low C+high Mn+high Cr+(Mo+V+Ni), and the present patent adopts medium C+low Cr+(Mo+Ni+Cu) composite addition; another aspect is the product performance and use, the present patent is suitable for die industry in S-containing and high-temperature H2O steam and other acidic environments, and CN113584379A does not have acid-resistant performance. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a high-hardness die steel plate with anti-HIC and SSCC double resistance performance and a manufacturing method, which adopts medium C, Cr and micro-alloy composite addition+rapid TMCP+high-temperature DQ cooling process to produce a steel plate with a mixed structure of martensite+behenite+long needle-shaped ferrite, the steel plate has a Vickers hardness≥400HV10, and the use requirements of die steel under acidic service conditions.

[0007] The technical scheme adopted by the present application to solve the above problems is: a high-hardness die steel plate with anti-HIC and SSCC double resistance performance, the chemical composition is as follows in terms of mass percentage: C 0.30-0.50%, Si 0.20-0.50%; P≤0.005%; S≤0.002%; Mn 0.50-0.80%; Al 0.02-0.04%; Nb≤0.01%; V≤0.01%; Cr 0.35-0.75%; Mo+Ni+Cu 0.15-0.25%; Ceq≤0.80; the balance is Fe and inevitable impurities.

[0008] The application designs to produce 8-90mm thickness steel plate by adopting medium C, Cr and micro-alloying compound addition + fast TMCP + high temperature DQ cooling process, finds specific regression equation through specific process parameters and corresponding high hardness performance, and the process and the regression equation are used in cooperation to produce unique microstructure; the steel plate with the unique microstructure can meet the double resistance performance of the steel plate, and has the use requirements of the die steel under the acid service condition, the Vickers hardness is greater than or equal to 400HV10.

[0009] In addition, the application also provides a manufacturing method of the high-hardness die steel under the acid service condition, and the specific production steps are as follows: KR molten iron pretreatment, BOF smelting, LF and RH furnace refining, slab continuous casting, hot delivery and hot charging, slab heating, fast TMCP rolling, high temperature DQ cooling, straightening, cooling bed cooling, stack slow cooling, steel plate shearing, and inspection and warehousing.

[0010] The functions of all the components contained in the application and the reasons for selecting the content are specifically described as follows:

[0011] C: C in the steel can increase yield and tensile strength, but too high C will adversely affect the toughness of the steel, and the C content in the application is selected in the range of 0.30-0.50%.

[0012] Si: Si can strengthen ferrite, improve strength, elastic limit and hardenability, but Si increases the overheating sensitivity and crack tendency of the steel, and the Si content in the application is determined in the range of 0.20-0.50%.

[0013] Mn: Mn is a good deoxidizer and desulfurizer, which can improve the toughness of the steel and reduce the ductile-brittle transition temperature, and Mn is also an element for improving the hardenability of the steel; but Mn segregation has an adverse effect on the acid resistance and toughness of the steel plate, and considering comprehensively, the Mn content in the application is designed in the range of 0.50-0.80%.

[0014] P, S: P can easily cause segregation during solidification in the steel, and easily cause ferrite solid solution strengthening and increase cold brittleness, and the P content in the application is determined in the range of ≤0.005%; S is an unavoidable impurity, which can easily produce thermal brittleness and reduce the ductility and toughness of the steel, and the S content in the application is determined in the range of ≤0.002%.

[0015] Al: Al is a deoxidizing element, which can play a role in refining grains by forming AlN, but too much Al content can easily form Al2O3 and other brittle inclusions in the molten steel during the smelting process, and reduce the purity of the molten steel. The Al content in the application is selected in the range of 0.02-0.04%.

[0016] Cr: Cr can improve the oxidation resistance and corrosion resistance of the steel, but at the same time, it reduces the impact toughness; meanwhile, part of Cr can replace iron to form alloy cementite, thereby improving the tempering stability of the steel; in comprehensive consideration, the content of Cr in the application is designed in the range of 0.35-0.75%.

[0017] Mo+Ni+Cu: Mo can refine the grain of the steel and improve the hardenability, but too much Mo can lead to the increase of strength and the decrease of toughness; Ni can improve the strength of the steel and maintain good plasticity and toughness, and Ni has good corrosion resistance, but Ni is scarce in resources and expensive in price; Cu can improve the atmospheric corrosion resistance and can improve the corrosion resistance of the material, but too much Cu can cause the steel to have a tendency of thermal brittleness; in comprehensive consideration, Mo, Ni and Cu are added in combination, and the total content is determined in the range of 0.15-0.25%.

[0018] In the component design, the medium C, Cr and micro-alloying are added in combination, and the medium C and Cr are highlighted; in the process, the rapid TMCP and high-temperature DQ cooling process are adopted, so that the material has a unique microstructure, and the structure has good double resistance and high hardness.

[0019] The application discloses a high-hardness die steel plate with double resistance of HIC and SSCC and a manufacturing method thereof.

[0020] (1) a steelmaking process, a KR molten iron pretreatment, a BOF converter smelting, an LF refining, an RH vacuum degassing treatment are adopted to produce high-purity molten steel, then a 365mm-thickness continuous casting machine is used to produce a continuous casting slab, after the continuous casting is completed, the continuous casting slab is subjected to slow cooling, the slow cooling time is greater than or equal to 6 hours, and then the continuous casting slab is hot sent and hot charged.

[0021] (2) the continuous casting slab is heated to 1160-1220 DEG C, and high-pressure water is used to remove the scale after the continuous casting slab is discharged; then two-stage rolling is carried out.

[0022] The first stage is a rough rolling stage: the rough rolling temperature is 1100-1160 DEG C, wherein the down-line temperature 1100 DEG C = the finishing rolling 1030 DEG C + 7 rough rolling passes * 10 DEG C temperature drop / pass, and the up-line temperature 1160 DEG C is determined according to the 1220 DEG C furnace discharge temperature after a high-pressure water initial descaling temperature drop of greater than or equal to 60 DEG C; the intermediate blank thickness in the stage is 2.0h-4.0h (h is the finished plate thickness), which can ensure the heating effect of the heating furnace and ensure that the finishing rolling has 5-9 rolling passes; meanwhile, the cumulative comprehensive reduction rate in the stage is greater than or equal to 60%, which can ensure that the austenite grains are completely crushed and provide superfine grains for the finishing rolling; the second stage is a finishing rolling stage: in order to ensure that the finish rolling temperature is greater than or equal to AC3+60 DEG C (AC3 = 800-880 DEG C), according to the pass temperature drop on the site, the finishing rolling open rolling is set to 1000-1060 DEG C, and the cumulative pass reduction rate of the finishing rolling is greater than or equal to 70%, so as to ensure that the deformation can be deep into the center of the plate and obtain more refined grains; the rolled plate is quickly sent to DQ (the plate speed is greater than or equal to 4.0 m / s), so as to ensure that the plate enters the DQ temperature is 900-950 DEG C, and then the DQ is quickly cooled (online rapid cooling), the cooling speed is controlled to be 15-25 DEG C / s, the water outlet temperature is 550-650 DEG C, and the plate is air-cooled after water outlet.

[0023] The present application adopts medium C, Cr and micro-alloying compound addition + fast TMCP + high temperature DQ cooling process to produce 8-90 mm thick steel plates, finds a specific regression equation through specific process parameters and corresponding high hardness performance, and the cooperation of the process and the regression equation can produce a unique microstructure; the steel plate with the unique microstructure can meet the double resistance performance of the steel plate, and has a Vickers hardness of greater than or equal to 400 HV10 and the use requirements of the die steel under the acid service condition.

[0024] The regression formula is determined according to specific process parameters (DQ inlet temperature, DQ outlet temperature) and corresponding hardness performance, the DQ inlet temperature and the DQ outlet temperature are mainly considered to determine the hardness performance of the plate, so only these two main factors are taken; the regression formula is derived according to the field experimental data and experimental detection results:

[0025] Z = -46897 + 92.5X + 14.69Y - 4.97*10 -2 X 2 -1.2425*10 -2 Y -2 , wherein: X is the DQ inlet temperature DEG C, Y is the DQ outlet temperature DEG C, and Z is the hardness performance HV10.

[0026] From the 3D graph, it can be concluded that the entering DQ temperature and the exiting DQ temperature will affect the hardness performance if they are too large or too small, the high point in the 3D graph is the best place for the hardness performance, so the control temperature is adopted at the place, and the best performance can be obtained, and the number of process experiments and the cost are reduced. The complex pure steel smelting technology is adopted to provide excellent billets, the medium C, the Cr and the micro-alloy composite addition + the fast TMCP + the high-temperature DQ cooling process are adopted to produce the steel plates with the thickness of 8-90mm, the specific regression equation is found through the specific process parameters and the corresponding high hardness performance, and the mixed structure composed of the martensite + the bainite + the long acicular ferrite can be produced by the cooperation of the process and the regression equation, and the hardness and the acid resistance of the steel can be greatly improved.

[0027] Compared with the prior art, the advantages of the present application are that:

[0028] (1) The complex pure steel smelting technology is adopted to provide excellent billets, the medium C, the Cr and the micro-alloy composite addition + the fast TMCP + the high-temperature DQ cooling process are adopted to produce the steel plates with the thickness of 8-90mm for the first time, and the specific regression equation is found through the specific process parameters and the corresponding hardness performance.

[0029] (2) The steel plate provided by the present application is produced by combining the fast TMCP and the high-temperature DQ process for the first time at home and abroad, and has a unique microstructure mainly composed of the mixed structure of the martensite + the bainite + the long acicular ferrite, can meet the double resistance performance requirements of the steel plate, and has the Vickers hardness of greater than or equal to 400HV10 and the use requirements of the die steel under the acid service condition. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is the cross-section crack situation of the HIC-resistant sample of the 10mm-thickness steel plate of the present application;

[0031] Figure 2 It is the cross-section crack situation of the HIC-resistant sample of the 65mm-thickness steel plate of the present application;

[0032] Figure 3 It is the microstructure photo of the 10mm-thickness steel plate of the present application at the 1 / 4 position along the plate thickness direction;

[0033] Figure 4 It is the microstructure photo of the 65mm-thickness steel plate of the present application at the 1 / 4 position along the plate thickness direction. DETAILED DESCRIPTION

[0034] The following describes a method for controlling rolling and cooling in the production of small and medium-sized CrV series spring steel hot-rolled wire rods according to a preferred embodiment of the present application. However, this embodiment is only a description of a preferred embodiment of the present application and should not limit the scope of the present application in any way. Any equivalent substitutions or changes made in accordance with the present application are within the scope of the present application.

[0035] Example 1-2:

[0036] According to the chemical composition range and manufacturing method of the present application, a new type of steel plate with unique microstructure, dual resistance and high hardness dual characteristics is manufactured through KR hot metal pretreatment - BOF smelting - LF and RH furnace refining - slab continuous casting - hot delivery and hot charging - slab heating - rapid TMCP rolling - high temperature DQ cooling - straightening - cold bed cooling - stack slow cooling - steel plate shearing - inspection and warehousing.

[0037] The specific process of the above heating, rapid TMCP rolling, and high temperature DQ cooling is as follows: a 365 mm thick continuous casting billet is heated to 1210°C, and the soaking section is kept at 40 min (Example 1) or a 365 mm thick continuous casting billet is heated to 1200°C, and the soaking section is kept at 30 min (Example 2), and high-pressure water is used to remove the scale after the continuous casting billet is discharged; then two-stage rolling is performed, the first stage rolling temperature is 1150-1160°C, the cumulative comprehensive reduction is ≥75%, and the intermediate billet thickness is 35 mm (Example 1) or the first stage rolling temperature is 1130-1140°C, the cumulative comprehensive reduction is ≥65%, and the intermediate billet thickness is 180 mm (Example 2); the second stage rolling temperature is 1050°C, and the cumulative pass reduction is 80% (Example 1) or the second stage rolling temperature is 1020°C, and the cumulative pass reduction is 85% (Example 2), and the final steel plate thickness is 10 mm (Example 1) and 65 mm (Example 2); high temperature DQ rapid cooling is performed after rolling, the DQ temperature is 940°C, the cooling rate is 22°C / s, and the water outlet temperature is 630°C (Example 1) and the DQ temperature is 920°C, the cooling rate is 18°C / s, and the water outlet temperature is 580°C (Example 2); then hot straightening is performed; and the steel plate is air-cooled on a cold bed after hot straightening.

[0038] The chemical composition of the test steel plate is shown in Table 1, the dual resistance performance and hardness performance are shown in Table 2, the HIC crack condition of the steel plate is shown in Figure 1 , Figure 2 , the microstructure is shown in Figure 3 and Figure 4 .

[0039] Table 1 Chemical composition of steel plate in Examples 1 and 2 (wt. %)

[0040] Example C Si Mn P S Al Nb V Cr Mo+Cu+Ni Ceq 1 0.39 0.23 0.60 0.003 0.0007 0.032 0.005 0.001 0.49 0.21 0.625 2 0.40 0.23 0.61 0.004 0.0006 0.031 0.004 0.001 0.49 0.22 0.626

[0041] Note: Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15

[0042] Table 2 Dual phase properties and hardness properties of steel sheets in Examples 1 and 2

[0043]

[0044] While the preferred embodiments of the application have been described above in detail, it is to be understood that various modifications and variations can be made to the application by those skilled in the art without departing from the spirit and principles of the application. None of the above citation is admitted to be prior art to the present application, which achieves the present application. Any citation of the above documents is intended as a citation of something shown by the document in connection with presenting its teachings and is not intended, and should not be construed, as an admission that the document is prior art to the present application.

Claims

1. A high hardness die steel plate having both HIC and SSCC resistance, characterized by The chemical composition of the steel plate is C 0.30-0.50%, Si 0.20-0.50%; P≤0.005%; S≤0.002%; Mn 0.50-0.80%; Al 0.02-0.04%; Nb ≤0.01%; V ≤0.01%; Cr 0.35-0.75%; Mo+Ni+Cu 0.15-0.25%; Ceq≤0.80; the balance being Fe and inevitable impurities; The thickness of the steel plate is 8-90mm; The metallographic structure of the steel plate is a mixed structure of martensite + bainite + long acicular ferrite; The Vickers hardness of the steel plate is ≥400HV10; The Vickers hardness of the steel plate is determined according to the following formula: Z = -46897 + 92.5X + 14.69Y - 4.97*10 -2 X 2 -1.2425*10 -2 Y -2 , Wherein: X is the DQ temperature ℃, Y is the DQ temperature ℃, Z is the hardness performance HV10.

2. A method of manufacturing a high hardness die steel plate having both HIC and SSCC resistance according to claim 1, characterized by: The method mainly comprises the following steps: 1) steelmaking process, using KR hot metal pretreatment, BOF converter smelting, LF refining, RH vacuum degassing treatment to produce high-purity molten steel, and then using continuous casting machine to produce continuous casting slab, after continuous casting, the continuous casting billet is subjected to slow cooling, the slow cooling time is ≥6 hours, and finally hot charging is performed; 2) heating the continuous casting billet to 1160-1220℃, using high-pressure water to remove the scale after the continuous casting billet is discharged; then two-stage rolling is carried out, the steel plate is quickly cooled after rolling, the cooling speed is controlled at 15-25℃ / s, air cooling is carried out after water is discharged, and then hot straightening is carried out, and the steel plate is air cooled on the cooling bed after hot straightening.

3. The method of claim 2, wherein the high hardness die steel plate having both HIC and SSCC resistance is manufactured by the steps of: The two-stage rolling specifically comprises: ​ The first stage is the rough rolling stage: the rolling temperature is 1100-1160℃, the thickness of the intermediate billet in this stage is 2.0h-4.0h, h is the thickness of the finished steel plate, the thickness in this range can ensure the heating effect of the heating furnace and ensure that there are 5-9 rolling passes in the finishing rolling; at the same time, the cumulative comprehensive reduction rate in this stage is ≥60%, which can ensure that the austenite grains are completely broken and provide ultra-fine grains for the finishing rolling; the second stage is the finishing rolling stage: in order to ensure that the finish rolling temperature is ≥AC3+60℃, AC3=800-880℃, according to the on-site pass temperature drop, the finishing rolling start rolling temperature is set to 1000-1060℃, and the finishing rolling cumulative pass reduction rate is ≥70%, which ensures that the deformation can penetrate to the center of the steel plate and obtain more refined grains.

4. The method of claim 3, wherein the high hardness die steel plate having both HIC and SSCC resistance is manufactured by the steps of: The rough rolling start rolling off-line temperature is 1100℃=the finishing rolling 1030℃+7 passes rough rolling*10℃ temperature drop / pass, and the on-line temperature is 1160℃, which is determined according to the 1220℃ discharge temperature and the ≥60℃ temperature drop after high-pressure water initial descaling. ​ 5. The method of claim 2, wherein the high hardness die steel plate having both HIC and SSCC resistance is manufactured by the steps of: The speed of the steel plate entering the DQ after rolling is ≥4.0m / s, the steel plate entering the DQ temperature is 900-950℃, and the water discharge temperature is 550-650℃. ​

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