CN111394658A - 980 MPa-grade cold-rolled Q & P steel suitable for conventional continuous annealing production line and manufacturing method thereof - Google Patents
980 MPa-grade cold-rolled Q & P steel suitable for conventional continuous annealing production line and manufacturing method thereof Download PDFInfo
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/08—Iron or steel
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G3/00—Apparatus for cleaning or pickling metallic material
- C23G3/02—Apparatus for cleaning or pickling metallic material for cleaning wires, strips, filaments continuously
Abstract
The invention provides 980 MPa-grade cold-rolled Q & P steel suitable for a conventional continuous annealing production line and a manufacturing method thereof, and the steel comprises the following components: c: 0.16-0.20%, Si: 0.6-1.0%, Mn: 1.8-2.0%, Nb: 0.05 to 0.07%, Ti: 0.02-0.03%, Al: 0.40-0.60 percent, less than or equal to 0.02 percent of P, less than or equal to 0.01 percent of S and the balance of Fe. The method adopts two-phase region annealing, heating to the temperature of 810-; the invention meets the requirements of high strength and plasticity, good cold forming performance, resource saving, cost reduction and the like of the steel for the automobile.
Description
Technical Field
The invention belongs to the technical field of material heat treatment, and particularly relates to 980 MPa-grade cold-rolled Q & P steel suitable for a conventional continuous annealing production line and a manufacturing method thereof.
Background
The weight reduction, energy conservation and emission reduction of the automobile and the improvement of the safety requirement promote the application of high-strength steel, particularly advanced high-strength steel in the automobile manufacturing. The first generation advanced high-strength steel represented by DP (Dual-Phase) steel has low alloy content, excellent formability and welding performance, is applied in a large amount at present, but the product of strength and elongation is low (generally within 15 GPa%), cannot meet the stamping and forming requirements of complex parts, and the parts have little collision energy absorption and cannot meet the increasingly developed requirements of automobile safety; although the strength product of the second-generation automobile steel represented by TWIP (twining Induced plasticity) steel reaches 50 GPa%, the second-generation automobile steel is hardly accepted by the market due to high alloy content and poor manufacturability and application performance; the Q & p (quenching and refining) steel, one of the third-generation advanced high-strength steels, is a third-generation automotive steel with high strength and toughness developed in recent years because it has high strength and plasticity and good comprehensive mechanical properties at the same time when a small amount of alloy elements are added.
The Q & P steel was originally proposed by Speer et al, the basic process route of which was: austenitizing is firstly carried out, and a high-Temperature austenite structure is obtained, and is rapidly cooled to a certain Temperature (QT) from Ms (martensite transformation starting Temperature) to Mf (martensite transformation finishing Temperature) for Quenching, and part of austenite is transformed into martensite; then heating to a certain distribution Temperature (PT), preserving heat for a period of time to carry out carbon distribution, diffusing and enriching supersaturated solid solution carbon in martensite into untransformed austenite, increasing the carbon content and stability of the untransformed austenite, and finally rapidly cooling to room Temperature. Through a quenching distribution process (Q & P process), the Q & P steel structure comprises certain retained austenite, so that the Q & P steel can keep higher tensile strength and higher elongation in the stretching process, and the aim of light weight of the automobile steel can be fulfilled.
The key to the Q & P process is two points: the first step of quenching process: after complete austenitization, rapidly cooling to a temperature of more than 100 ℃ below the Ms temperature to obtain a certain amount of martensite to ensure that the material has sufficient strength; the second step of distribution process: the rapidly cooled steel plate is rapidly heated to a certain temperature near the Ms point for distribution, and the distribution of C from martensite to austenite is an important factor for stabilizing the retained austenite in the process, so that more retained austenite can be obtained and the stability of the retained austenite can be improved. According to the production process of Q & P steel, the product is generally produced in a special production line for high-strength steel having high-temperature heating, rapid cooling, and post-cooling induction heating capabilities.
Patent document CN201210092207.7 discloses an ultra-high strength steel plate for cold forming, wherein the elongation of the steel plate at 1000MPa level can reach 18-22%, and the elongation of the steel plate at 1200MPa level can reach 13-15%. Although the performance indexes of the third-generation steel are achieved, the production process needs to be carried out by heating to austenitizing and preserving heat in a continuous annealing production line with rapid cooling treatment, and then carrying out distribution treatment in a hood-type annealing furnace. The process has long flow, high cost and high requirement on production line.
Patent document No. 200910077392.0 discloses a C-Mn-Al Q system&P steel, method for producing the same, and Q&P steel tensile strength of 886MPa or more and elongation (A)50mm) Greater than 20.0%, and has better product of strength and elongation. The process is realized in a laboratory, the Al content in the component design is generally more than 1.3%, and metallurgical defects such as inclusions and the like easily occur in the actual production and smelting process. The annealing temperature in the heat treatment process is more than 850 ℃, and the conventional continuous annealing line cannot be realized.
Patent document CN201610792298.3 describes a cold-rolled quenched ductile steel and a method for manufacturing the same, which is produced by a "one-step" Q & P process, but in order to improve the plasticity of the steel sheet, the composition design thereof is to add 1.3-1.8% of Si to suppress the precipitation of cementite during the partitioning process. However, the excessively high Si content makes the surface of the steel sheet susceptible to formation of an oxide layer during hot rolling, and the oxide layer is broken during subsequent rolling and partially enters the surface of the steel, resulting in a reduction in the surface quality of the finished product. Meanwhile, three-stage heating is adopted in the annealing and heating stage in the one-step Q & P process, so that the process is complex.
Patent document CN201810144307.7 introduces a 980MPa grade cold-rolled high-strength Q & P steel for automobiles and a production method thereof, and the provided Q & P steel has tensile strength of more than or equal to 980MPa, elongation of more than or equal to 18 percent and good cold forming performance. However, because the one-step partitioning process is adopted, the quenching end temperature is high, the martensite content is insufficient, so that the high C, Mn element needs to be added in the component design to improve the strength, which is unfavorable for the welding performance of the material, and meanwhile, 0.5-1.0% of Al is added in the component, so that metallurgical defects such as inclusion and the like are easy to occur, and the surface quality is unfavorable.
The patent document with the application number of CN201510504662.7 introduces a niobium alloying TAM steel and a manufacturing process thereof, wherein the adopted new process adds a complete austenitizing and quenching process (heating to the austenitizing temperature of 900 ℃ at 10 ℃/s and preserving the temperature of 920 ℃ for 600s, and then cooling to the room temperature at 50 ℃/s) before the conventional continuous annealing, and the added process has higher requirements on equipment, and cannot be realized in large-scale production at present.
The patent document with the application number of CN201610297645.5 introduces a Q & P steel plate and a two-time distribution preparation method thereof, the tensile strength of the steel plate produced by the method introduced by the patent is more than or equal to 1200MPa, the elongation is more than or equal to 20 percent, and the product of strength and elongation is more than or equal to 25 GP.
Disclosure of Invention
The invention aims to provide 980 MPa-grade cold-rolled Q & P steel suitable for a conventional continuous annealing production line, which is characterized in that Nb and Ti are properly added on the basis of C-Si-Mn steel, a hot-rolled structure is refined, and the diffusion of alloy elements is facilitated; on the other hand, the element Nb can also lower the Ms temperature, lower the overaging distribution temperature and suppress the formation of carbides. Meanwhile, through reasonable selection and mutual cooperation of a critical annealing austenitizing system, quenching system and a partitioning system, the content of residual austenite in the steel is improved to the greatest extent, and the content of austenite is 8-15%, so that the product of strength and elongation of the steel is greatly improved through the TRIP effect of the residual austenite, and the requirements of high strength and plasticity, good cold forming performance, resource saving, cost reduction and the like of the automobile steel are met.
The invention also aims to provide a manufacturing method of 980MPa grade cold-rolled Q & P steel suitable for a conventional continuous annealing production line.
The specific technical scheme of the invention is as follows:
a980 MPa-grade cold-rolled Q & P steel manufacturing method suitable for a conventional continuous annealing production line comprises the following production and manufacturing process flows: smelting → continuous casting → hot rolling → acid pickling and cold rolling → continuous annealing → finished product.
Further, smelting: the method is suitable for smelting of converters, electric furnaces and induction furnaces;
furthermore, a casting blank is produced by adopting continuous casting, and a dynamic soft reduction and electromagnetic stirring system can be used for ensuring the quality of the casting blank;
further, the hot rolling comprises: heating the casting blank at 1200-1260 ℃, and preserving the heat for 2-3 hours; the final rolling temperature is 870 ℃ and 910 ℃; and winding the steel coil at the temperature of 540 ℃ and 600 ℃.
Preferably, the hot rolling is specifically: heating the casting blank at 1200-1260 ℃, preserving heat for 2-3 hours, carrying out 5-7 times of rolling by a roughing mill, carrying out 5-7 times of rolling to obtain an intermediate blank of 30-50mm, carrying out 5-7 times of rolling by a hot continuous rolling mill unit, carrying out 870-910 ℃ of final rolling temperature, coiling to obtain a steel coil within the range of 540-600 ℃ after rolling to the target thickness, and obtaining uniform and fine hot rolled tissues;
acid pickling and cold rolling: pickling the hot-rolled strip steel by a hydrochloric acid tank, removing surface iron scales, performing cold continuous rolling or cold rolling, wherein the cold rolling reduction rate is 50-70%, and rolling to the target thickness.
And (3) continuous annealing: heating the steel plate treated in the acid-washing and cold-rolling step to 810-850 ℃ for two-phase region annealing, slowly cooling to 720-760 ℃, then rapidly cooling to 260-300 ℃ for quenching, then heating to 340-380 ℃ for distribution, and finally cooling to room temperature.
Preferably, the continuous annealing: heating the steel plate treated in the pickling and cold rolling step to 810-850 ℃ and preserving heat for 90-170 seconds to carry out two-phase region annealing to obtain 60-80% of austenitizing effect; then slowly cooling to 720-760 ℃ at a cooling speed of 3-5 ℃/s, and precipitating a small amount of proeutectoid ferrite in the process; then cooling to 260-300 ℃ at a cooling rate of more than or equal to 25/s for quenching, wherein part of austenite is transformed into martensite in the process; then heating to 340-380 ℃ for isothermal 380-720s for distribution, wherein C in supersaturated martensite is diffused to untransformed austenite in the process, so that the austenite is rich in carbon; and finally cooling to room temperature, and retaining the carbon-rich austenite to the room temperature to obtain 8-15% of retained austenite.
The annealing curves in conjunction with FIG. 1 illustrate: the lower the quenching temperature, the higher the martensite content in the final structure and the higher the strength. The higher the distribution temperature is, the more sufficient the distribution process is, the higher the content of the retained austenite in the final structure is, and the higher the elongation of the material is, and meanwhile, the higher the distribution temperature is, the higher the tempering degree of the martensite is, and the strength of the material is reduced. For a conventional continuous annealing line, no rapid heating equipment is arranged after quenching, the temperature rise capability is limited, and the maximum temperature rise is about 80-100 ℃. In the invention, the diffusion distance of C in the distribution process is shortened by adding the refining elements of trace Nb and Ti in the components. If the quenching temperature is lower than 260 ℃, enough martensite is obtained, and higher strength can be obtained, but the temperature is not enough to be raised to a reasonable distribution temperature for a conventional continuous annealing line, so that the content of residual austenite in a finished product is insufficient, and the performance is represented by high strength and low elongation; on the contrary, the quenching temperature is higher than 300 ℃, the martensite content in the final product is less, and the performance of the final product is represented by low strength and high elongation. For the distribution temperature, if the distribution temperature is lower than 300 ℃, the C diffusion power is insufficient, the content of the residual austenite of the finished product is low, and the elongation is poor; under the quenching temperature (260-.
The 980 MPa-grade cold-rolled Q & P steel manufactured by the method and suitable for a conventional continuous annealing production line comprises the following components in percentage by mass:
c: 0.16-0.20%, Si: 0.6-1.0%, Mn: 1.8-2.0%, Nb: 0.05 to 0.07%, Ti: 0.02-0.03%, Al: 0.40-0.60 percent, less than or equal to 0.02 percent of P, less than or equal to 0.01 percent of S and the balance of Fe.
The design principle of each element and content of the invention is as follows:
c: the carbon content directly affects the martensite transformation point and the enrichment of carbon into austenite during heat treatment results in a decrease in the Ms point temperature. Carbon can stabilize austenite, the strength of the steel plate is insufficient due to the low carbon content, and sufficient C atoms are not enriched into the retained austenite in the distribution process, so that the stability of the obtained retained austenite is insufficient. However, since too high a carbon content is disadvantageous in formability and weldability, it is not generally preferable that the higher the carbon content is. In the present invention, the content of C is controlled to be in a lower range of 0.16 to 0.20%.
Si: ferrite forming elements which play a role in solid solution strengthening; can prevent cementite from being precipitated and play a role in stabilizing austenite; on the other hand, too high a silicon content causes selective oxidation of the surface of the steel sheet during annealing, and scales are generated during heating, and when scales are pressed into the surface of the sheet during hot rolling, the surface quality of the sheet is deteriorated, which causes difficulty in welding the material, difficulty in hot galvanizing, poor coating properties of the surface layer, and the like. Therefore, the weight percentage of Si in the invention is controlled as follows: 0.6 to 1.0 percent.
Mn: the strength of a ferrite matrix is improved through the solid solution strengthening effect, and Ac can be reduced by increasing the content of Mn element1And Ac3Temperature, realizing low-temperature critical zone annealing; the other function of adding Mn element into the low-carbon steel is to shift the pro-eutectoid ferrite precipitation line to the right, so that the precipitation amount of ferrite in the annealing and cooling process is less to ensure the content of residual austenite in the final microstructure. Too high Mn content may lead to increased austenite volume, severe band structure of the steel, and high cost and processing difficulty. Therefore, the Mn content of the invention is controlled to be 1.8-2.0% by weight.
Nb: the strengthening elements are separated out, the effect of refining crystal grains is achieved, uniform and fine finished product structures are obtained, and the method is beneficial to improving the strength and the elongation of finished products. Meanwhile, the addition of trace Nb element refines the annealed austenite grains, and reduces the Ms temperature, so that the steel of the invention can complete the distribution process at a lower temperature, and is more beneficial to being realized on a conventional continuous annealing line. The Nb content of the invention is controlled between 0.05 and 0.07 percent by weight.
Ti: the steel is added with a trace amount of Ti, so that the strength of the steel can be improved, the effects of precipitation strengthening and grain refining are achieved, the TiN can effectively prevent austenite from growing in the heating process during heating, the effect of refining austenite grains is achieved, meanwhile, the toughness of a welding heat affected zone can be improved, and the welding performance of the material is improved. The Ti content of the invention is controlled between 0.02 and 0.03 percent by weight.
Al: while adding a trace amount of aluminum during smelting, deoxidation can be carried out, but excessive Al can block a nozzle during continuous casting, so that the difficulty of continuous casting is increased, and therefore, the content of Als is preferably controlled to be 0.4-0.6%.
P, S: the content of P, S in the steel is strictly controlled in order to reduce the adverse effect of harmful impurities in the steel on the punching properties of the steel.
When the Q & P steel alloy elements are designed, the content of the Nb element is properly increased, the hot rolling structure is refined, and the diffusion of the alloy elements during annealing is facilitated; meanwhile, the austenite grains are refined and annealed, the Ms temperature is reduced, and the adjustment of the process window of the distribution temperature (overaging temperature) of the conventional continuous annealing line is facilitated; and trace Ti is added to refine austenite grains, so that the toughness of a welding heat affected zone can be improved, and the welding performance of the material can be improved. The invention has the advantages of economic and reasonable components and excellent welding performance and is suitable for the conventional continuous annealing production line.
Compared with the prior art, in the aspect of components, noble metal elements such as Ni and Mo are not added, the C, Mn content is relatively low, and trace Ti is mainly used for refining hot-rolled austenitized grains and welding performance; nb is used for refining grains to improve the strength and the plasticity; on the other hand, the hot rolling structure is refined, so that the free diffusion path of alloy elements in the annealing process is shortened, and the diffusion of the alloy elements in the annealing process is facilitated; meanwhile, the crystal grains are refined, the Ms point is reduced, the isothermal distribution temperature is reduced, and the precipitation of carbide in the overlong overaging isothermal process of the production line of the conventional continuous annealing process is favorably inhibited. In the aspect of process, the invention adopts two-phase region annealing, the annealing temperature is lower, and the method can be implemented on the conventional continuous annealing production line; on the other hand, by reasonably controlling the quenching temperature and the distribution (overaging) temperature (the difference between the quenching temperature and the distribution (overaging) temperature is smaller and not more than 100 ℃, and the difference is larger, a special production line induction heating is required), so that the method is beneficial to the existing continuous annealing production line without special induction heating and long-time overaging, can be directly implemented, and does not need to modify and input equipment. 980 MPa-grade cold-rolled Q for automobiles produced by adopting alloy component design and continuous annealing process&The yield strength of the P steel plate is 550-650MPa, the tensile strength is more than or equal to 980MPa, and the elongation (A)50) Not less than 20 percent, the product of strength and elongation not less than 20 GPa%, and has good weldability and processing formability, and resources are savedAnd the cost is reduced, and the use requirements of the cold-rolled high-strength steel for the automobile are met.
Drawings
FIG. 1 is a schematic diagram of a continuous annealing process of the present invention;
FIG. 2 shows SEM structure (10000 ×) of 980MPa class Q & P steel product of the present invention, wherein F-ferrite, M-martensite, RA: retained austenite;
FIG. 3 is an SEM structure for a comparative example 1Q & P steel product;
FIG. 4 is an SEM structure for a comparative example 2Q & P steel product;
FIG. 5 is an SEM structure for a comparative example 3Q & P steel product;
Detailed Description
The invention is further described below by means of specific examples.
Examples 1 to 9
980 MPa-grade cold-rolled Q & P steel suitable for a conventional continuous annealing production line is disclosed, and the chemical composition mass percentage of the steel is shown in Table 1.
The manufacturing method of 980MPa cold-rolled Q & P steel suitable for the conventional continuous annealing line described in the embodiment 1-9 comprises the following steps:
smelting → continuous casting → hot rolling → acid pickling and cold rolling → continuous annealing → finished product.
The method specifically comprises the following steps:
(1) smelting and continuous casting: the method is suitable for smelting in a converter, an electric furnace and an induction furnace, continuous casting is adopted to produce a casting blank, and an electromagnetic stirring and dynamic soft reduction device is used in the pouring process to reduce component segregation in the solidification process;
(2) hot continuous rolling of a casting blank or ingot: heating the casting blank at the temperature of 1200-1260 ℃, preserving heat for 2-3 hours, carrying out 5-7 times of rolling by a roughing mill, carrying out 5-7 times of rolling to an intermediate blank of 30-50mm, carrying out 5-7 times of rolling by a hot continuous rolling mill set, carrying out 870-910 ℃ of final rolling temperature, and coiling to form a steel coil within the range of 540-600 ℃ after the target thickness is achieved;
(3) acid pickling and cold rolling: pickling the hot-rolled strip steel by a hydrochloric acid tank, removing surface iron oxide scales, performing cold continuous rolling or cold rolling, wherein the cold rolling reduction rate is 50-70%, and rolling to the target thickness;
(4) and (3) continuous annealing: annealing the acid-rolled sample by using a continuous annealing production line, wherein the parameters of the continuous annealing process of the embodiments 1 to 9 are shown in a table 1; the properties of the products produced are shown in table 1.
Comparative examples 1 to 3
The chemical composition of the cold rolled steel is shown in the mass percentage in table 1.
The process for producing cold rolled steel as described in comparative example 1 is the same as examples 1-9, except for the ingredients listed in table 1 (no Nb, Ti additions).
The cold rolled steel of comparative examples 2-3 was produced by the same process as examples 1-9, except for the annealing process as set forth in table 1.
TABLE 1 composition, production Process parameters and Properties of the steels of the examples and comparative examples
FIG. 2 shows SEM structure (10000 ×) of 980MPa class Q & P steel product of the present invention, wherein F-ferrite, M-martensite, RA: retained austenite;
FIG. 3 is an SEM structure for a comparative example 1Q & P steel product; no addition of Nb and Ti, relatively large crystal grains and low content of residual austenite;
FIG. 4 is an SEM structure for a comparative example 2Q & P steel product; low-temperature quenching and low-temperature partitioning, high martensite content, low residual austenite content, high strength and poor elongation.
FIG. 5 is an SEM structure for a comparative example 3Q & P steel product; high-temperature quenching and high-temperature distribution, the martensite content is low, the tempering characteristic is achieved, and the strength is insufficient.
980 MPa-grade cold-rolled Q for automobiles produced by using alloy composition design and continuous annealing process&The yield strength of the P steel plate is 550-650MPa, the tensile strength is more than or equal to 980MPa, and the elongation (A)50) Not less than 20 percent, the product of strength and elongation not less than 20GPa, good weldability and processing formability, resource saving,the cost is reduced, and the use requirements of the cold-rolled high-strength steel for the automobile are met.
Claims (10)
1. A980 MPa-grade cold-rolled Q & P steel manufacturing method suitable for a conventional continuous annealing production line comprises the following production and manufacturing process flows: smelting → continuous casting → hot rolling → acid pickling cold rolling → continuous annealing → finished product, which is characterized in that the continuous annealing is: heating to 810-850 ℃ to perform two-phase region annealing, slowly cooling to 720-760 ℃, then rapidly cooling to 260-300 ℃ to perform quenching, then heating to 340-380 ℃ to perform distribution, and finally cooling to room temperature.
2. The method as claimed in claim 1, wherein the two-phase annealing is performed by heating to 810-850 ℃ for 90-170 seconds.
3. The manufacturing method according to claim 1 or 2, wherein the slow cooling is slow cooling at a cooling rate of 3 to 5 ℃/s.
4. The method as claimed in any one of claims 1 to 3, wherein the rapid cooling is performed at a cooling rate of at least 25/s to a temperature of at least 260 ℃ and at least 300 ℃.
5. The method as claimed in any one of claims 1 to 4, wherein the distribution is performed by heating to 340 ℃ and 380 ℃ for 380-720 s.
6. The manufacturing method according to claim 1, wherein the hot rolling includes: the heating temperature of the casting blank is 1200-1260 ℃, and the temperature is kept for 2-3 hours.
7. The method as claimed in claim 1, wherein said hot rolling comprises a finish rolling temperature of 870-.
8. The method as claimed in claim 1, wherein the hot rolling comprises coiling at 600 ℃ and 540 ℃ to form a steel coil.
9. The manufacturing method according to claim 1, wherein the acid pickling cold rolling: pickling the hot-rolled strip steel by a hydrochloric acid tank, removing surface iron scales, performing cold continuous rolling or cold rolling, wherein the cold rolling reduction rate is 50-70%, and rolling to the target thickness.
10. A 980MPa grade cold-rolled Q & P steel suitable for a conventional continuous annealing line manufactured by the manufacturing method according to any one of claims 1 to 9, characterized in that the 980MPa grade cold-rolled Q & P steel suitable for a conventional continuous annealing line comprises the following components in percentage by mass:
c: 0.16-0.20%, Si: 0.6-1.0%, Mn: 1.8-2.0%, Nb: 0.05 to 0.07%, Ti: 0.02-0.03%, Al: 0.40-0.60 percent, less than or equal to 0.02 percent of P, less than or equal to 0.01 percent of S and the balance of Fe.
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| CN112048681A (en) * | 2020-09-07 | 2020-12-08 | 鞍钢股份有限公司 | 980 MPa-grade high-formability cold-rolled DH steel and preparation method thereof |
| CN113416887A (en) * | 2021-05-21 | 2021-09-21 | 鞍钢股份有限公司 | Automobile super-high formability 980 MPa-grade galvanized steel plate and preparation method thereof |
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