A low-cost thin-gauge high-strength steel plate subcritical online quenching production method

Abstract

The present application relates to the technical field of steel plate production, and particularly relates to a low-cost thin-gauge high-strength steel plate sub-temperature online quenching production method, which comprises the following steps: a continuous casting billet sequentially passes through heating, rolling, pre-straightening, sub-temperature online quenching, hot straightening, low-temperature straightening and offline tempering to obtain a thin-gauge high-strength steel plate with a thickness H, 8mm<=H<=16mm; the sub-temperature online quenching process specifically comprises the following steps: directly performing online quenching on the pre-straightened steel plate, the open cooling temperature is 720-760 DEG C, the cooling speed is > 25 DEG C / s, and the final cooling temperature is 200+ / -20 DEG C. Through the sub-temperature quenching method, the yield strength of the quenched steel plate is controlled to be 850-900 MPa, and the temperature is controlled to be 200+ / -20 DEG C, the strength and the temperature can realize low-temperature straightening of a hot straightening machine, and high-flatness plate shape is obtained, a good plate shape foundation is created for heat treatment tempering, the process flow is shortened, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of steel plate production technology, specifically to a low-cost, thin-gauge, high-strength steel plate sub-temperature online quenching production method. Background Technology

[0002] High-strength steel plates are widely used in various engineering machinery, such as cranes, bulldozers, excavators, transport vehicles, dump trucks, hydraulic supports, and other structural components in mining and various construction projects. With the nation's vigorous promotion of carbon neutrality and peak carbon emissions, lightweight development of medium and heavy plate products will inevitably become mainstream. Lightweighting means that while the thickness of the steel plate decreases, its strength needs to be further improved; this will increase the demand for thin-gauge high-strength steel products.

[0003] Currently, many medium and heavy plate production lines in China use online quenching technology, enabling them to mass-produce high-strength steel plates with a thickness of 20mm or more. However, due to the poor plate shape and inability to temper thin high-strength steel plates (thickness below 16mm) after online quenching, order delivery is affected. Therefore, the current heat treatment process for thin high-strength steel plates mainly employs offline quenching and tempering. This process has a long production cycle, low efficiency, high energy consumption, and high production costs. Chinese patent CN105369021A discloses an online quenching and cooling method that balances the plate shape and performance of thin high-strength steel plates. The method involves heating the billet to 1180~1240℃, using a conventional hot rolling process, controlling the final rolling temperature of the steel plate to ≥900℃, and using a MULPIC device for quenching and cooling. The hot-rolled steel plate is rapidly fed into the MULPIC device via a roller conveyor for high-volume water cooling, with an initial cooling temperature of 750~800℃. The method uses a MULPIC device with a short cooling zone, which limits its use to large-volume online quenching of thin sheets. Furthermore, it demands high precision and stable control of the MULPIC device, and introducing new production equipment increases production costs. Therefore, there is a need for a high-strength, thin-sheet product and its production method that can accommodate different sheet sizes while utilizing existing equipment. Summary of the Invention

[0004] To address the high production cost of online quenching processes for thin-gauge high-strength steel, this invention provides a low-cost production method for thin-gauge high-strength steel plates and sub-temperature online quenching. Through rational composition design, rolling, sub-temperature online quenching, hot straightening, low-temperature straightening, and heat treatment tempering, thin-gauge high-strength steel plates with low cost, high flatness, high performance, and high efficiency can be produced.

[0005] A low-cost, thin-gauge high-strength steel plate production method for sub-temperature online quenching includes: continuously cast billets sequentially undergoing heating, rolling, pre-straightening, sub-temperature online quenching, hot straightening at low temperature, and offline tempering to obtain thin-gauge high-strength steel plates with a thickness of 8~16mm; the sub-temperature online quenching process specifically involves: directly subjecting the pre-straightened steel plate to online quenching, with an initial cooling temperature of 720~760℃, a cooling rate >25℃ / s, and a final cooling temperature of 200±20℃.

[0006] After preliminary process testing and verification, the above-mentioned sub-temperature online quenching process controls the yield strength of the quenched steel plate at 850~900MPa. By controlling the strength and temperature of the steel plate, the difficulty of low-temperature straightening of the hot straightener is greatly reduced, and a high flatness plate shape can be obtained, which creates a good plate shape foundation for heat treatment tempering. This shortens the process flow and reduces production costs.

[0007] Furthermore, by mass percentage, the chemical composition of the continuously cast billet includes C 0.14%~0.17%, Si 0.20%~0.40%, Mn 1.35%~1.50%, P < 0.002%, S < 0.005%, Als 0.020%~0.05%, Nb 0.010%~0.025%, with the remainder being Fe and unavoidable impurities.

[0008] Furthermore, the heating process specifically involves heating the continuously cast billet at a temperature of 1160~1220℃ for a furnace time of 8~10 min / cm.

[0009] Furthermore, the rolling process is as follows: the target thickness of the thin-gauge high-strength steel plate is H. When 12mm≤H≤16mm, a two-stage controlled rolling mode of flat rolling is adopted; the roughing rolling start temperature is 1020~1060℃, and the intermediate billet thickness is 3.5H; the finishing rolling last pass reduction rate is controlled at 9%~12%; single-pass rolling is adopted, and the final rolling temperature is 740~780℃; when 8mm≤H<12mm, a flat rolling + coil rolling mode is adopted; the start rolling temperature is 1020~1060℃; the coil rolling last pass reduction rate is controlled at 9%~12%; single-pass rolling is adopted, and the final rolling temperature is 780~820℃.

[0010] Furthermore, the pre-straightening process parameters are set as follows: the side roller position is -5~1mm, and the bending roller position is -30~40mm; adjust the inlet and outlet roller gaps according to different thickness specifications: when 8mm≤H<12mm, the inlet roller gap is 4~8mm, and the outlet roller gap is 6~12mm; when 12mm≤H<14mm, the inlet roller gap is 8~10mm, and the outlet roller gap is 8~14mm; when 14mm≤H≤16mm, the inlet roller gap is 10~12mm, and the outlet roller gap is 10~16mm.

[0011] Pre-straightening not only releases the internal stress generated during rolling, but also flattens the poorly shaped plates, laying the foundation for the plate shape in the subsequent online quenching process.

[0012] Furthermore, the low-temperature straightening process is as follows: the steel plate is sent to the hot straightening machine for low-temperature straightening. When 12mm≤H≤16mm, a 9-roll system with a roll diameter of 285mm is used to straighten the steel plate in 1 to 3 passes.

[0013] When 8mm≤H<12mm, use an 11-roll system with a roll diameter of 220mm to straighten the steel plate in 1 to 3 passes.

[0014] Furthermore, the specific parameter settings in the low-temperature straightening process are as follows: the position of the side roller is -5~1mm, and the position of the bending roller is -30~40mm; the inlet and outlet roller gaps are adjusted according to different thickness specifications: when 8mm≤H<12mm, the inlet roller gap is 2~8mm, and the outlet roller gap is 6~12mm; when 12mm≤H<14mm, the inlet roller gap is 4~10mm, and the outlet roller gap is 8~14mm; when 14mm≤H≤16mm, the inlet roller gap is 6~12mm, and the outlet roller gap is 10~16mm.

[0015] Furthermore, the offline tempering process is as follows: heat the steel plate to 600~640℃, hold for 2.0~2.2min / mm and hold for ≥30min.

[0016] Furthermore, the yield strength of thin-gauge high-strength steel plates is 550~750MPa, the tensile strength is 640~940MPa, the elongation after fracture is ≥16%, and the longitudinal low-temperature impact energy at -20℃ is ≥47J.

[0017] Furthermore, the microstructure of the thin-gauge high-strength steel plate consists of tempered sorbite and undissolved ferrite, with the undissolved ferrite distributed between the tempered sorbite, dividing the tempered sorbite matrix. Since cracks are difficult to propagate at the interface between the undissolved ferrite and tempered sorbite, and during crack propagation, the undissolved ferrite hinders crack initiation and propagation through its own plastic deformation, the strength and toughness of the steel plate are greatly improved.

[0018] The beneficial effects of this invention are as follows:

[0019] 1. The sub-temperature online quenching method for producing thin-gauge high-strength steel plates provided by this invention uses sub-temperature quenching, with the temperature controlled at 200±20℃, to control the yield strength of the steel plate at 850~900MPa. This strength and temperature allow for low-temperature straightening using a hot straightener, resulting in a high-flatness plate shape. This creates a good plate shape foundation for heat treatment tempering, eliminating the need for new rapid cooling devices and reducing production equipment costs. Furthermore, this invention employs an online quenching process, eliminating the reheating process in traditional quenching and tempering processes, shortening the process flow, reducing energy consumption, and improving production efficiency.

[0020] 2. The thin-gauge high-strength steel plate produced by the present invention using a sub-temperature online quenching process allows undissolved ferrite to inhibit the initiation and propagation of cracks through its own plastic deformation, thereby improving the strength and toughness of the steel plate. Furthermore, the use of low-temperature rolling combined with sub-temperature online quenching preserves defects such as dislocations generated during the rolling process, further enhancing the strength of the thin-gauge high-strength steel plate. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a photograph of the sheet shape of the thin-gauge high-strength steel in Example 1.

[0023] Figure 2 This is a micrograph of the metallographic structure of thin-gauge high-strength steel before tempering in Example 1.

[0024] Figure 3 This is a micrograph of the metallographic structure of the thin-gauge high-strength steel after tempering in Example 1.

[0025] Figure 4 This is a photograph of the sheet shape of the thin-gauge high-strength steel in Example 2.

[0026] Figure 5 This is a micrograph of the metallographic structure of thin-gauge high-strength steel before tempering in Example 2.

[0027] Figure 6 This is a micrograph of the metallographic structure of the thin-gauge high-strength steel after tempering in Example 2. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0029] Example 1

[0030] 16mm thick high-strength steel plate Q550D is produced using 150mm thick continuously cast billets on a 3500mm single-stand hot roll mill production line.

[0031] The continuously cast billet contains the following chemical composition in percentage: C 0.16%, Si 0.3%, Mn 1.4%, P < 0.002%, S < 0.005%, Als 0.03%, Nb 0.015%, with the remainder being Fe and unavoidable impurities.

[0032] The production method specifically includes the following steps:

[0033] (1) Heating: The 150mm continuous casting billet is heated at 1180℃ for 120min.

[0034] (2) Rolling: The two-stage control rolling mode of flat rolling is adopted, with single-pass rolling, 6 passes of roughing rolling and 5 passes of finishing rolling; the initial rolling temperature of roughing rolling is 1040℃, and the thickness of the intermediate billet is 56mm; the reduction rate of the last pass of finishing rolling is 9%, rolling the steel plate to 16mm; the final rolling temperature is 760℃.

[0035] (3) Pre-straightening: The rolled steel plate is sent to the pre-straightening machine for straightening. The inlet roll gap is 12mm, the outlet roll gap is 16mm, the side roll position is 0, and the bending roll is 2mm.

[0036] (4) Sub-temperature online quenching: The pre-straightened steel plate is directly quenched online with an initial cooling temperature of 740℃, a cooling rate of 30℃ / s, and a final cooling temperature of 180℃.

[0037] (5) Hot straightening and low temperature straightening: The steel plate is then sent to a 9-roll hot straightening machine with a roll diameter of 285mm for online low temperature straightening. The inlet roll gap is 8mm, the outlet roll gap is 15mm, the side roll position is -3mm, and the bending roll is -30mm.

[0038] (6) Offline tempering: The steel plate after low temperature straightening is heated to 640℃, held for 32 minutes, and then air-cooled to room temperature to obtain a 16mm thick high-strength steel plate.

[0039] The thin-gauge high-strength steel plate obtained in this embodiment has the following shape: Figure 1 As shown, the unevenness is ≤3mm / m, and the plate shape is good and without defects.

[0040] Samples of the steel plate before tempering were taken and tested, and its microstructure was as follows: Figure 2 As shown, the microstructure is a multiphase microstructure of martensite and undissolved ferrite.

[0041] Samples were taken from the tempered steel plates for testing, and their microstructure was as follows: Figure 3 As shown, the microstructure consists of tempered sorbite and undissolved ferrite, with the undissolved ferrite distributed between the tempered sorbite, dividing the tempered sorbite matrix.

[0042] The mechanical properties of the 16mm thick high-strength steel plate prepared in this embodiment were tested. The specific results are as follows: yield strength is 621MPa, tensile strength is 790MPa, elongation after fracture is 20%, and longitudinal low-temperature impact energy at -20℃ is 156J.

[0043] Example 2

[0044] 10mm thick high-strength steel plate Q690D is produced using 150mm thick continuously cast billets on a 3500mm single-stand hot roll mill production line.

[0045] The continuously cast billet contains the following chemical composition in percentage: C 0.16%, Si 0.3%, Mn 1.4%, P < 0.002%, S < 0.005%, Als 0.03%, Nb 0.015%, with the remainder being Fe and unavoidable impurities.

[0046] The production method specifically includes the following steps:

[0047] (1) Heating: The 150mm continuous casting billet is heated at 1200℃ and the time in the furnace is 120min.

[0048] (2) Rolling: The rolling mode of flat rolling + coil rolling is adopted, and the rolling is carried out in a single pass, including 6 passes of flat rolling and 5 passes of coil rolling; the initial rolling temperature is 1040℃, the reduction rate of the last pass of coil rolling is 12%, and the steel plate is rolled to 10mm; the final rolling temperature is 800℃.

[0049] (3) Pre-straightening: The rolled steel plate is sent to the pre-straightening machine for straightening. The inlet roll gap is 2mm, the outlet roll gap is 10mm, the side roll position is -2mm, and the bending roll is 3mm.

[0050] (4) Sub-temperature online quenching: The pre-straightened steel plate is directly quenched online with an initial cooling temperature of 740℃, a cooling rate of 30℃ / s, and a final cooling temperature of 200℃.

[0051] (5) Hot straightening and low temperature straightening: The steel plate is then sent to an 11-roll hot straightening machine with a roll diameter of 220mm for online low temperature straightening. The inlet roll gap is 3mm, the outlet roll gap is 6mm, the side roll position is 2mm, and the bending roll is 40mm.

[0052] (6) Offline tempering: Heat the steel plate after low temperature straightening to 600℃, hold for 30 minutes, and then air cool to room temperature to obtain a 10mm thick high-strength steel plate.

[0053] The thin-gauge high-strength steel plate obtained in this embodiment has the following shape: Figure 4 As shown, the unevenness is ≤3mm / m, and the plate shape is good and without defects.

[0054] Samples of the steel plate before tempering were taken and tested, and its microstructure was as follows: Figure 5 As shown, the microstructure is a multiphase microstructure of martensite and undissolved ferrite.

[0055] Samples were taken from the tempered steel plates for testing, and their microstructure was as follows: Figure 6 As shown, the microstructure consists of tempered sorbite and undissolved ferrite, with the undissolved ferrite distributed between the tempered sorbite, dividing the tempered sorbite matrix.

[0056] The mechanical properties of the 10mm thick high-strength steel plate prepared in this embodiment were tested. The specific results are as follows: yield strength is 748MPa, tensile strength is 814MPa, elongation after fracture is 18%, and longitudinal low-temperature impact energy at -20℃ is 130J.

[0057] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for the intercritical on-line quenching of low-cost thin-gauge high-strength steel sheets, characterized in that, The method comprises the following steps: The continuous casting billet is heated, and the heating temperature is 1160-1220 DEG C, and the furnace time is 8-10 min / cm.

2. The subcritical online quench production method of claim 1, wherein, The rolling process is as follows: when 12mm≤H≤16mm, the flat rolling two-stage controlled rolling mode is adopted; the rough rolling opening rolling temperature is 1020-1060 DEG C, and the intermediate billet thickness is 3.5H; the final pass reduction rate of the finish rolling is controlled to be 9%-12%; single pass rolling is adopted, and the finish rolling temperature is 740-780 DEG C; when 8mm≤H<12mm, the flat rolling+coil rolling rolling mode is adopted; the opening rolling temperature is 1020-1060 DEG C; the final pass reduction rate of the coil rolling is controlled to be 9%-12%; single pass rolling is adopted, and the finish rolling temperature is 780-820 DEG C.

3. The subcritical online quench production method of claim 1, wherein, The pre-straightening process parameters are set as follows: the edge roller position is-5-1mm, and the bending roller position is-30-40mm; according to different thickness specifications, the inlet and outlet roller gaps are adjusted: when 8mm≤H<12mm, the inlet roller gap is 4-8mm, and the outlet roller gap is 6-12mm; when 12mm≤H<14mm, the inlet roller gap is 8-10mm, and the outlet roller gap is 8-14mm; when 14mm≤H≤16mm, the inlet roller gap is 10-12mm, and the outlet roller gap is 10-16mm.

4. The subcritical online quench production method of claim 1, wherein, The low-temperature straightening process is as follows: the steel plate is sent to the hot straightening machine for low-temperature straightening; when 12mm≤H≤16mm, the 9-roller roller system with a roller diameter of 285mm is used to straighten the steel plate for 1-3 passes; when 8mm≤H<12mm, the 11-roller roller system with a roller diameter of 220mm is used to straighten the steel plate for 1-3 passes.

5. The subcritical online quench production method of claim 1, wherein The low-temperature straightening process parameters are set as follows: the edge roller position is-5-1mm, and the bending roller position is-30-40mm; according to different thickness specifications, the inlet and outlet roller gaps are adjusted: when 8mm≤H<12mm, the inlet roller gap is 2-8mm, and the outlet roller gap is 6-12mm; when 12mm≤H<14mm, the inlet roller gap is 4-10mm, and the outlet roller gap is 8-14mm; when 14mm≤H≤16mm, the inlet roller gap is 6-12mm, and the outlet roller gap is 10-16mm.

6. The subcritical online quench production method of claim 5, wherein, ​ 7. The subcritical online quench production method of claim 1, wherein, The offline tempering process is that the steel plate is heated to 600-640 DEG C, the holding time is 2.0-2.2 min / mm and the holding time is greater than or equal to 30 min.

8. The subcritical online quench production method of claim 1, wherein, The yield strength of the thin-gauge high-strength steel plate is 550-750 MPa, the tensile strength is 640-940 MPa, the elongation after fracture is greater than or equal to 16%, and the longitudinal low-temperature impact energy at-20 DEG C is greater than or equal to 47 J.

9. The subcritical online quench production process of claim 1, wherein, The microstructure of the thin-gauge high-strength steel plate is tempered sorbite and undissolved ferrite, the undissolved ferrite is distributed between the tempered sorbite, and the tempered sorbite matrix is divided.

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