A production method of high-strength automobile beam steel 800L-AC steel

Abstract

The application relates to the technical field of steel rolling, and particularly discloses a production method of high-strength automobile beam steel 800L-AC steel, which reconfigures alloy element components; the billet is heated; the heating temperature of a heating furnace, total furnace time and soaking section residence time are controlled; rolling parameters are set, including the finish rolling inlet temperature, the final rolling temperature, the coiling temperature and the cooling strategy of the billet, the rough rolling scale removal pass and the load distribution of the finish rolling mill are controlled; the work roll bending force and the roll shifting amount are automatically adjusted according to the plate shape defect type, and the plate shape defect is corrected in real time; the load distribution technology is adopted to control the rolling force deviation of each rack within + / -8%, so that the excessive bending of the roll system caused by local overload is avoided, and the plate shape defect is reduced from the source; the work roll bending force and the roll shifting amount are automatically adjusted according to the plate shape defect type (edge wave and middle wave), the real-time correction of the plate shape defect is realized, the plate shape qualified rate is improved, and the strength and toughness of the steel are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of steel rolling technology, specifically to a production method of 800L-AC steel grade for high-strength automotive beams. Background Technology

[0002] As a core load-bearing structural component of automobiles, the steel used in automotive beams has extremely stringent technical requirements, necessitating a balance between high strength, high toughness, and excellent formability and weldability. Different grades correspond to different strength levels. Taking the currently mainstream 700L grade automotive beam steel as an example, its yield strength ≥700 MPa, the ability to resist plastic deformation, is a core indicator of lightweighting; its tensile strength of 780~950 MPa, the ability to resist fracture, is an important guarantee of safety; its elongation of 18%~25% measures plasticity, ensuring no cracking during stamping; its low-temperature impact toughness ≥100 J (-40℃), ensuring resistance to brittle fracture during service in cold regions; its cold bending performance is qualified with a 180° wide cold bend D=0; and it undergoes rigorous formability testing with a bending mandrel diameter of zero, simulating harsh bending conditions.

[0003] However, the existing 700L grade automotive beam steel has an optimal low-carbon equivalent weldable yield strength of over 750 MPa. Although the yield strength is ≥750 MPa, the tensile strength is 780~950 MPa, and the elongation is 15%, it is not clearly stated whether it possesses good low-temperature toughness. Furthermore, the alloy cost is relatively high, which not only increases production costs but may also pose safety hazards due to insufficient toughness when used in cold regions. The 700MPa grade automotive beam steel plate suffers from severe segregation in the cast billet due to problems in the continuous casting process. Uneven distribution of Ti element leads to mixed crystal phenomena, reduced impact toughness, and S element segregation causes delamination of the tensile fracture surface, ultimately resulting in stamping cracks. Therefore, it is necessary to explore a production method for high-strength 800L-AC steel for automotive beams to solve the problem of stamping cracking in the current 700L grade automotive beam steel. Summary of the Invention

[0004] In view of the problems existing in the prior art, the purpose of this invention is to provide a production method for 800L-AC steel grade high-strength automotive beam steel.

[0005] The technical solution adopted by this invention to solve its technical problem is: a production method of 800L-AC steel for high-strength automotive beams, comprising the following steps:

[0006] S1. Alloy element composition: The standard composition of the steel billet by mass percentage is as follows: C: 0.065~0.095%, Si: 0.15~0.25%, Mn: 1.80~1.90%, P≤0.015%, S≤0.005%, Ti: 0.115~0.140%, Nb: 0.055~0.065%, Als: 0.020~0.045%, N≤0.0060%;

[0007] S2. Steel billet heating: Controlling the heating temperature of the heating furnace, the total time in the furnace, and the residence time in the soaking zone;

[0008] S3. Rolling parameters: The billet rolling process sets the finishing mill inlet temperature, finishing mill temperature, coiling temperature, and cooling strategy to control the number of roughing mill descaling passes and the load distribution of the finishing mill.

[0009] S4. Automatically adjust the bending force and roll displacement of the work roll according to the type of plate defect, and correct the plate defect in real time.

[0010] Specifically, the target values ​​for the mass percentage of the chemical composition of the steel billet in step S1 are: C: 0.080%, Si: 0.20%, Mn: 1.85%, P≤0.010%, S≤0.002%, Ti: 0.120%, Nb: 0.060%, Als: 0.030%, N≤0.0045%.

[0011] Specifically, in step S2, the thickness of the steel billet is 10.0~14.0mm, the temperature of the first heating section of the heating furnace is 1290±20℃, the temperature of the soaking section is 1280±20℃, and the target tapping temperature is 1230±30℃.

[0012] Specifically, the furnace time for steel billets entering the furnace as cooled billets is ≥200 minutes, the residence time in the soaking zone is ≥40 minutes, and the total residence time in the first heating zone and the soaking zone is ≥80 minutes; the furnace time for steel billets entering the furnace as hot billets is ≥180 minutes, the residence time in the soaking zone is ≥35 minutes, and the total residence time in the first heating zone and the soaking zone is ≥80 minutes.

[0013] Specifically, in step S3, when the thickness of the steel billet is 10.0~14.0mm, the finishing rolling inlet temperature is 1050±20℃, the final rolling temperature is 880±15℃, the coiling temperature is 610±15℃, and the cooling strategy adopts front-end low-pressure intensive cooling.

[0014] Specifically, in step S3, the roughing descaling passes adopt a 3+3 roughing descaling pass, the F1~F2 stands of the finishing mill bear 30%~35% of the total rolling force, the F3~F5 stands bear 40%~45% of the total rolling force, and the F6~F7 stands bear 20%~25% of the total rolling force. The rolling force deviation of each stand is controlled within ±8%, and the total reduction rate of the F3~F7 stands is ≥60%. During the rolling process, water spray cooling technology between stands is adopted to control the temperature difference between stands at 30-50℃.

[0015] Specifically, in step S4, the plate defects include edge waviness and center waviness. When edge waviness occurs, the bending force of the work rolls on stands F3 to F7 is increased to 1000 to 1500 kN to suppress edge extension. When center waviness occurs, the roll shifting amount is adjusted by ±50 to 100 mm to change the contact length of the work rolls and balance the rolling force between the center and the edge. The response time of the entire adjustment process is ≤0.5 s.

[0016] The present invention has the following beneficial effects:

[0017] The production method of 800L-AC steel for high-strength automotive beams designed in this invention employs load distribution technology to control the rolling force deviation of each stand within ±8%, avoiding excessive bending of the roll system caused by local overload and reducing plate defects from the source. Based on the type of plate defect (edge ​​waviness, center waviness), the bending force and roll shifting of the work rolls are automatically adjusted to achieve real-time correction of plate defects, improve the plate qualification rate, and significantly enhance the strength and toughness of the steel. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be described clearly, completely, and in further detail below. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0019] Example 1

[0020] Producing 800L-ACH steel with a thickness of 10.0~12.0mm. This includes the following steps:

[0021] 1. Alloy element composition: The standard composition of the steel billet by mass percentage is as follows: C: 0.080%, Si: 0.20%, Mn: 1.85%, P: 0.010%, S: 0.002%, Ti: 0.120%, Nb: 0.060%, Als: 0.030%, N: 0.0045%.

[0022] 2. Steel billet heating: Control the temperature of the first heating section of the heating furnace to 1290℃, the temperature of the soaking section to 1280℃, and the target tapping temperature to 1230℃.

[0023] 3. Rolling parameters: The billet rolling parameters are set as follows: finishing mill inlet temperature is 1050℃, final rolling temperature is 880℃, coiling temperature is 610℃, and the cooling strategy adopts low-pressure intensive cooling in the front section. The billet is placed in the furnace as a cooled billet for 210 minutes, the soaking zone residence time is 42 minutes, and the total residence time of the first heating section and the soaking zone is 81 minutes.

[0024] The roughing descaling passes employ a 3+3 roughing descaling pass system, with one ultra-high pressure pass and one high pressure pass in the finishing mill. The entry temperature into the finishing mill is 1050℃, ensuring high surface quality while maintaining uniform temperature, resulting in better subsequent strip shape. Load distribution technology: Based on the rolling force distribution characteristics of 2250mm ultra-wide strip (the rolling force at the edges is 10%~15% higher than at the center), the load distribution of each stand is optimized. Stands F1~F2 of the finishing mill bear 30%~35% of the total rolling force, stands F3~F5 bear 40%~45%, and stands F6~F7 bear 20%~25%. The rolling force deviation of each stand is controlled within ±8%, avoiding excessive bending of the roll system due to local overload, and reducing strip shape defects from the source.

[0025] 4. The bending force and roll displacement of the work roll are automatically adjusted according to the type of plate defect, and the plate defect is corrected in real time.

[0026] Plate shape defects include edge waviness and center waviness. When edge waviness occurs, the bending force of the work rolls on stands F3 to F7 is increased to 1000 to 1500 kN to suppress edge extension. When center waviness occurs, the roll shifting amount is adjusted by ±50 to 100 mm to change the contact length of the work rolls and balance the rolling force between the center and the edge. The response time of the entire adjustment process is ≤0.5s, realizing real-time correction of plate shape defects. The plate shape qualification rate is increased from less than 60% in the traditional process to more than 98%.

[0027] Precise control of the finishing mill's final rolling temperature at 820-840℃ (within the non-recrystallization region of austenite), with a total reduction rate of ≥60% for stands F3-F7, generates a large number of dislocations and subgrain boundaries in austenite grains through cumulative deformation (total deformation ≥85%), inhibiting grain growth. During the rolling process, "inter-stand water spray cooling" technology is used to control the temperature between stands to drop to 30-50℃, ensuring that each stand is rolled in the non-recrystallization region. Ultimately, the ferrite grain size of the finished steel is refined to below 10μm, which is 40%-50% finer than traditional processes, significantly improving the strength and toughness of the steel.

[0028] Example 2

[0029] Producing 800L-ACH steel with a thickness of 12.1~14.0mm. This includes the following steps:

[0030] 1. Alloy element composition: The standard composition of the steel billet by mass percentage is as follows: C: 0.095%, Si: 0.25%, Mn: 1.90%, P: 0.015%, S: 0.005%, Ti: 0.140%, Nb: 0.065%, Als: 0.045%, N: 0.0060%.

[0031] 2. Billet heating: The temperature of the first heating section of the heating furnace is controlled at 1310℃, the temperature of the soaking section is 1300℃, and the target tapping temperature is 1260℃. The billet is charged into the furnace as a hot billet and spends 190 minutes in the furnace, 38 minutes in the soaking section, and a total of 80 minutes in the first heating section and the soaking section.

[0032] 3. Rolling parameters: The billet rolling is set with a finishing mill inlet temperature of 1070℃, a finishing mill temperature of 895℃, a coiling temperature of 625℃, and a front-end low-pressure intensive cooling strategy.

[0033] The roughing descaling passes employ a 3+3 roughing descaling pass system, with one ultra-high pressure pass and one high pressure pass in the finishing mill. The entry temperature into the finishing mill is 1050℃, ensuring high surface quality while maintaining uniform temperature, resulting in better subsequent strip shape. Load distribution technology: Based on the rolling force distribution characteristics of 2250mm ultra-wide strip (the rolling force at the edges is 10%~15% higher than at the center), the load distribution of each stand is optimized. Stands F1~F2 of the finishing mill bear 30%~35% of the total rolling force, stands F3~F5 bear 40%~45%, and stands F6~F7 bear 20%~25%. The rolling force deviation of each stand is controlled within ±8%, avoiding excessive bending of the roll system due to local overload, and reducing strip shape defects from the source.

[0034] 4. The bending force and roll displacement of the work roll are automatically adjusted according to the type of plate defect, and the plate defect is corrected in real time.

[0035] Plate shape defects include edge waviness and center waviness. When edge waviness occurs, the bending force of the work rolls on stands F3 to F7 is increased to 1000 to 1500 kN to suppress edge extension. When center waviness occurs, the roll shifting amount is adjusted by ±50 to 100 mm to change the contact length of the work rolls and balance the rolling force between the center and the edge. The response time of the entire adjustment process is ≤0.5s, realizing real-time correction of plate shape defects. The plate shape qualification rate is increased from less than 60% in the traditional process to more than 98%.

[0036] Precise control of the finishing mill's final rolling temperature at 820-840℃ (within the non-recrystallization region of austenite), with a total reduction rate of ≥60% for stands F3-F7, generates a large number of dislocations and subgrain boundaries in austenite grains through cumulative deformation (total deformation ≥85%), inhibiting grain growth. During the rolling process, "inter-stand water spray cooling" technology is used to control the temperature between stands to drop to 30-50℃, ensuring that each stand is rolled in the non-recrystallization region. Ultimately, the ferrite grain size of the finished steel is refined to below 10μm, which is 40%-50% finer than traditional processes, significantly improving the strength and toughness of the steel.

[0037] This invention will be used to produce 800L-ACH grade steel. Upon reaching full production capacity, the project will have an annual capacity of 300,000 tons, increasing the added value per ton of steel by 50 yuan compared to other products, and generating an additional net profit of 15 million yuan annually. It will also drive the development of the automotive parts processing and logistics supply chain. Breaking through the technological bottleneck of ultra-wide high-strength steel, it will promote the transformation of my country's steel industry towards high-end development, increase the localization rate of automotive steel to over 95%, and enhance the self-controllability of the supply chain. The project's construction and operation will directly create 10 jobs and indirectly create 200 jobs in upstream and downstream industries, cultivating a group of professionals in high-strength steel rolling processes. Ultra-wide specifications reduce welding joints, increasing the fatigue life of commercial vehicle beams by 30%, reducing the risk of traffic accidents, and ensuring road transport safety. Process optimization will reduce furnace energy consumption by 10%, saving 12,000 tons of standard coal annually; it will also reduce iron oxide scale generation by 5%, reducing solid waste emissions. It will promote a 10% weight reduction in commercial vehicles. Based on 100,000 kilometers of annual driving per 10,000 commercial vehicles, this will reduce fuel consumption by 12 million liters and CO2 emissions by 32,000 tons annually. The low-alloy design reduces the consumption of rare metals, while the product has a recyclability rate of over 95%, which meets the requirements for the development of a circular economy.

[0038] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

[0039] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A method for producing 800L-AC steel grade high-strength automotive frame steel, characterized in that, Includes the following steps: S1. Alloy element composition: The standard composition of the steel billet by mass percentage is as follows: C: 0.065~0.095%, Si: 0.15~0.25%, Mn: 1.80~1.90%, P≤0.015%, S≤0.005%, Ti: 0.115~0.140%, Nb: 0.055~0.065%, Als: 0.020~0.045%, N≤0.0060%; S2. Steel billet heating: Controlling the heating temperature of the heating furnace, the total time in the furnace, and the residence time in the soaking zone; S3. Rolling parameters: The billet rolling process sets the finishing mill inlet temperature, finishing mill temperature, coiling temperature, and cooling strategy to control the number of roughing mill descaling passes and the load distribution of the finishing mill. S4. Automatically adjust the bending force and roll displacement of the work roll according to the type of plate defect, and correct the plate defect in real time.

2. The production method of the high-strength automotive beam steel 800L-AC grade according to claim 1, characterized in that, The target values ​​for the mass percentage of the chemical composition of the steel billet in step S1 are: C: 0.080%, Si: 0.20%, Mn: 1.85%, P≤0.010%, S≤0.002%, Ti: 0.120%, Nb: 0.060%, Als: 0.030%, N≤0.0045%.

3. The production method of the high-strength automotive beam steel 800L-AC grade according to claim 1, characterized in that, In step S2, the thickness of the steel billet is 10.0~14.0mm, the temperature of the first heating section of the heating furnace is 1290±20℃, the temperature of the soaking section is 1280±20℃, and the target tapping temperature is 1230±30℃.

4. The production method of the high-strength automotive beam steel 800L-AC grade according to claim 3, characterized in that, The furnace time for steel billets entering the furnace as cold billets is ≥200 minutes, the residence time in the soaking zone is ≥40 minutes, and the total residence time in the first heating zone and the soaking zone is ≥80 minutes; the furnace time for steel billets entering the furnace as hot billets is ≥180 minutes, the residence time in the soaking zone is ≥35 minutes, and the total residence time in the first heating zone and the soaking zone is ≥80 minutes.

5. The production method of the high-strength automotive beam steel 800L-AC grade according to claim 3, characterized in that, In step S3, when the thickness of the steel billet is 10.0~14.0mm, the finishing rolling inlet temperature is 1050±20℃, the final rolling temperature is 880±15℃, the coiling temperature is 610±15℃, and the cooling strategy adopts front-end low-pressure intensive cooling.

6. The production method of the high-strength automotive beam steel 800L-AC grade according to claim 1, characterized in that, In step S3, the roughing descaling passes adopt a 3+3 roughing descaling pass. The F1~F2 stands of the finishing mill bear 30%~35% of the total rolling force, the F3~F5 stands bear 40%~45% of the total rolling force, and the F6~F7 stands bear 20%~25% of the total rolling force. The rolling force deviation of each stand is controlled within ±8%, and the total reduction rate of the F3~F7 stands is ≥60%. During the rolling process, water spray cooling technology between stands is used to control the temperature difference between stands at 30-50℃.

7. The production method of high-strength automotive beam steel 800L-AC grade according to claim 6, characterized in that, In step S4, the plate defects include edge waviness and center waviness. When edge waviness occurs, increase the bending force of the work rolls on stands F3 to F7 to 1000 to 1500 kN to suppress edge extension. When center waviness occurs, adjust the roll shifting amount by ±50 to 100 mm to change the contact length of the work rolls and balance the rolling force between the center and the edge. The response time of the entire adjustment process is ≤0.5 s.