CN111549288A - Automobile girder steel with thickness of 12.0-16.0 mm and high toughness of 700MPa and production method thereof - Google Patents
Automobile girder steel with thickness of 12.0-16.0 mm and high toughness of 700MPa and production method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- 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
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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
- 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
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- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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Abstract
The invention discloses automobile girder steel with the thickness of 12.0-16.0 mm and the high toughness of 700MPa and a production method thereof, wherein the girder steel comprises the following chemical components in percentage by weight: 0.06-0.09%, Si: 0.10 to 0.30%, Mn: 1.60-1.90%, P is less than or equal to 0.020%, S is less than or equal to 0.005%, Alt: 0.020 to 0.050%, Nb: 0.04-0.06%, Ti: 0.06-0.10% of N, less than or equal to 0.0050% of N, and the balance of Fe and inevitable impurities; its preparing process is also disclosed. The metallographic structure of the automobile girder steel is ferrite and pearlite, wherein the pearlite content is less than 10%, and the grain size is more than or equal to 12 grade.
Description
Technical Field
The invention relates to the technical field of thick high-strength steel production, in particular to automobile beam steel which has high strength, excellent plasticity, low-temperature impact toughness and welding performance, is mainly used for automobile structural members such as automobile beams and longitudinal beams which require good forming and processing performances and have high strength requirements, and particularly relates to automobile beam steel with the thickness of 12.0-16.0 mm and the high toughness of 700MPa and a production method thereof.
Background
Along with the development of economy, automobiles occupy more and more important positions in industrial and agricultural production and daily life of people, and meanwhile, the common application of automobiles brings about various problems such as energy consumption, environmental pollution and the like while bringing convenience to the production and the life of people. Therefore, the light weight of the automobile becomes an important subject of sustainable development of the automobile industry, the light weight of the automobile is to reduce the equipment quality of the automobile as much as possible on the premise of ensuring the strength and the safety performance of the automobile, the weight reduction of the automobile is the most effective energy-saving means besides improving the combustion efficiency of an engine, and meanwhile, the weight reduction of the automobile body can also save raw materials, reduce the cost of automobile production enterprises, improve the benefit and reduce the carbon emission of raw material supply enterprises. In the special automobile industry, the high-strength steel plate is used, the thickness of the girder steel plate can be reduced, the self weight of the girder is reduced, the method is one of the most effective means for reducing the weight of the automobile, the weight of the whole automobile can be obviously reduced, the load is improved, and the service life of the automobile is prolonged. After the special automobile is lightened, the transportation efficiency can be improved, the logistics cost is greatly reduced, the energy-saving and emission-reducing social benefits are remarkable, and compared with the traditional common steel plate, the special automobile has incomparable advantages.
The automobile beam is a heavy load-bearing part in a vehicle body structure, bears frequent alternating loads of pulling, pressing, bending and twisting, and has high requirement on the stability of mechanical performance. The crossbeam steel plate is used for manufacturing structural members such as automobile longitudinal beams, cross beams, front and rear axles, bumpers and the like, the thickness is generally 3.0-10.0 mm, the steel plate is large in demand in automobile structural steel and is one of steel types with high performance index requirements. The automobile beam is a main part of a truck and almost bears the whole weight of cargos, so that the quality of the beam directly influences the service life and the driving safety of the whole truck. However, some heavy trucks cannot improve their service life by reducing their weight, for example, trucks for pulling heavy equipment can only raise the strength grade of the steel beam of the truck and put forward higher requirements on strength and toughness matching under the same thickness specification, so the demand of the steel beam of the truck with the thickness specification of 12.0mm or more is increased year by year.
At present, high-strength automobile beam steels which are produced and widely used at home and abroad mainly comprise 610L, 650L, 700L, 750L and the like, steel enterprises capable of producing comprise Bao steel, Wu steel, saddle steel, package steel, Tai steel, Lai steel, An steel, Chengde steel and the like, meanwhile, high-strength automobile beam steels with the yield strength of 700MPa gradually enter the steel market for automobiles of domestic and foreign commercial vehicles, and the high-strength automobile beam steels comprise BS700MC developed by Bao steel, WL700 developed by Wu steel, A700L developed by saddle steel, TH800 developed by Tai steel, AG700MC developed by An steel, BT700 developed by package steel, LG700L developed by Lai steel, C700L developed by bearing steel and the like.
Zhao Bei Lin et al (Zhao Bei Lin et al, 700MPa super strength automobile beam steel research and development, steel rolling, 3 rd, 4 months 2011) produced 700MPa automobile beam steel by Nb and Ti microalloy, and the strength and elongation index of the 6mm thick test steel meet the requirements, but the value of impact toughness is not given in the text.
The method is characterized in that the Tokyo et al (Tokyo et al, trial production of 700MPa grade high-strength automobile side beam steel, Hebei metallurgy, 2016, 9 th year) utilizes V, Ti composite micro-alloying in a steel bearing company to produce 700MPa grade automobile girder steel with the thickness of 5.8mm by a 1780 continuous rolling mill set, but the chemical composition design contains 0.07-0.10V, the production cost is high, and the width and the thickness of a steel plate are limited.
The patent CN103849812A discloses a low-brittleness 700 MPa-level steel for automobile beams and a manufacturing method thereof, wherein the thickness range is 3.0-12.0 mm, but only the mechanical property index of a steel plate with the thickness of 10.0mm is given. The patent CN108315639A discloses a high-toughness 600 MPa-grade automobile girder steel and a production method thereof, wherein the tensile strength is 600-700 MPa, the yield strength is more than or equal to 500MPa, the elongation is more than or equal to 20%, the maximum steel plate is 7.8mm, but the strength is lower. Patent CN109161806A discloses a700 MPa-level automobile beam steel belt and a preparation method thereof, and only discloses that the mechanical property is 14.0mm in thickness, and the thickness specification is single.
In short, the 700MPa grade automotive frame steel according to the above documents and patents has technical problems that the thickness specification does not break through 14.0mm, the strength is low, and the like.
Disclosure of Invention
The invention aims to provide automobile girder steel with the thickness of 12.0-16.0 mm and the high toughness of 700MPa and a production method thereof, wherein the metallographic structure of the automobile girder steel is ferrite and pearlite, the content of the pearlite is less than 10%, and the grain size is more than or equal to 12.
In order to solve the technical problems, the invention adopts the following technical scheme:
the automobile girder steel with the thickness of 12.0-16.0 mm and the high toughness of 700MPa and the production method thereof are disclosed, wherein the girder steel comprises the following chemical components in percentage by weight: 0.06-0.09%, Si: 0.10 to 0.30%, Mn: 1.60-1.90%, P is less than or equal to 0.020%, S is less than or equal to 0.005%, Alt: 0.020 to 0.050%, Nb: 0.04-0.06%, Ti: 0.06-0.10 percent of N, less than or equal to 0.0050 percent of N, and the balance of Fe and inevitable impurities.
Preferably, the chemical composition of the beam steel is, by weight percent, C: 0.07 to 0.09%, Si: 0.15 to 0.25%, Mn: 1.70-1.85%, P is less than or equal to 0.015%, S is less than or equal to 0.003%, Alt: 0.030-0.045%, Nb: 0.045-0.055%, Ti: 0.065-0.90%, N is less than or equal to 0.0035%, and the balance is Fe and inevitable impurities.
The production method comprises the following steps: the method comprises the following steps of molten iron pretreatment, converter combined blowing, RH refining, continuous casting, slab heating, hot continuous rolling, laminar cooling and coiling; the hot continuous rolling process comprises rough rolling and finish rolling;
the continuous casting slab is continuously cast to form a continuous casting billet, and the continuous casting billet comprises the following chemical components in percentage by weight: c: 0.06-0.09%, Si: 0.10 to 0.30%, Mn: 1.60-1.90%, P is less than or equal to 0.020%, S is less than or equal to 0.005%, Alt: 0.020 to 0.050%, Nb: 0.04-0.06%, Ti: 0.06-0.10 percent of N, less than or equal to 0.0050 percent of N, and the balance of Fe and inevitable impurities.
In the continuous casting billet heating step, the continuous casting billet is heated to 1190-1230 ℃, and the furnace time is controlled within 200-260 min, such as 200min, 210min, 220min, 230min, 240min, 250min, 260min and the like.
The invention adopts two-stage controlled rolling process of rough rolling and finish rolling, namely austenite recrystallization region rolling and austenite non-recrystallization region rolling, so that the steel can obtain a deformed austenite structure storing large deformation energy while finishing rolling, further obtain a fine phase change structure, and improve the strength of the steel through fine grain strengthening.
The rough rolling is carried out by adopting a 3+3 model 2-frame rolling mill, the rough rolling initial rolling temperature is 1120-1190 ℃, such as 1120 ℃, 1130 ℃, 1140 ℃,1150 ℃, 1160 ℃, 1170 ℃, 1180 ℃,1190 ℃ and the like, the rough rolling initial reduction is 25.0-37.0 mm, such as 25.0mm, 27.0mm, 29.0mm, 31.0mm, 33.0mm, 35.0mm, 37.0mm and the like.
In the finish rolling step, the finish rolling is finished by adopting a 7-rack continuous variable-crown rolling mill, and the initial rolling temperature of the finish rolling is 950-1100 ℃.
The thickness of the intermediate blank in the finish rolling and the initial rolling is 3.4-4.6 times of the thickness of the finished steel plate, the finish rolling reduction rate is more than 70%, and the finish rolling temperature is 820-860 ℃.
The laminar cooling adopts a front section cooling mode, the cooling speed is 20-40 ℃/s, and the coiling temperature is 590-610 ℃.
Compared with the prior art, the invention has the beneficial technical effects that:
according to the invention, low-carbon manganese steel is taken as a base, microalloy elements such as niobium and titanium are added in a compounding manner, the niobium and titanium improve the recrystallization temperature through precipitation strengthening, and the strength and the low-temperature impact toughness of the steel are improved through grain refinement, but if the content is improper or the heating temperature is low, undissolved phases can be formed, and the strength and the impact toughness can be influenced. However, the inventor finds that the high-strength hot-rolled automobile beam steel strip with the thickness of 12.0-16.0 mm and the pressure of 700MPa, which is developed by adopting the raw material components and the mass ratio provided by the invention and combining the controlled rolling and the controlled cooling process and adopting a 2250mm hot-rolling production line, has good formability, low-temperature toughness and fatigue property, is successfully applied to the manufacture of heavy commercial vehicles, and has the following beneficial effects:
the invention provides a high-toughness 700 MPa-grade automobile beam steel strip with the thickness of 12.0-16.0 mm, which contains the following components by reasonable component design: 0.06-0.10%, Nb: 0.04-0.06% of microalloy elements, a microstructure of ferrite and pearlite, a grain size of about 13 grade, high strength, excellent processing and forming properties, excellent welding properties and the like, and the steel is suitable for automobile structural members such as automobile beams, longitudinal beams and the like. The mechanical property and the process property meet the requirements that the yield strength is more than or equal to 620MPa, the tensile strength is 720-850 MPa, the elongation A is more than or equal to 18 percent, and the cold bending d is 2a, and the impact value at minus 20 ℃ is more than or equal to 80J.
Drawings
The invention is further illustrated in the following description with reference to the drawings.
FIG. 1 is a typical metallographic structure of an example of the present invention.
Detailed Description
The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.
In a first embodiment of the invention, the invention provides a high-toughness 700 MPa-grade automotive girder steel strip with the thickness of 12.0-16.0 mm, and the balance of chemical components of the girder steel strip in percentage by weight is C: 0.06-0.09%, Si: 0.10 to 0.30%, Mn: 1.60-1.90%, P is less than or equal to 0.020%, S is less than or equal to 0.005%, Alt: 0.020 to 0.050%, Nb: 0.04-0.06%, Ti: 0.06-0.10%, N is less than or equal to 0.0050%, and Fe and inevitable impurities. For example, the 700MPa automotive frame steel strip provided by the invention comprises the following chemical components in percentage by weight: c: 0.06%, Si: 0.30%, Mn: 1.85%, P is less than or equal to 0.017%, S is less than or equal to 0.003%, Alt: 0.050%, Ti: 0.085%, Nb: 0.045%, N: 0.0045%, the balance being Fe and unavoidable impurities; or C: 0.08%, Si: 0.10%, Mn: 1.65 percent, P is less than or equal to 0.017 percent, S is less than or equal to 0.002 percent, Alt: 0.020%, Ti: 0.065%, Nb: 0.045%, N: 0.0030%, the balance being Fe and unavoidable impurities; or C: 0.07%, Si: 0.15%, Mn: 1.70 percent, less than or equal to 0.015 percent of P, less than or equal to 0.002 percent of S, Alt: 0.030%, Ti: 0.070%, Nb: 0.050%, N: 0.0025%, the balance being Fe and unavoidable impurities; and the like.
In a second embodiment of the invention, the invention further provides a preparation method of the automobile beam steel strip with the thickness of 12.0-16.0 mm and the high toughness of 700MPa, which comprises the following steps: the method comprises the following steps of molten iron pretreatment, converter combined blowing, RH refining, continuous casting, slab heating, hot continuous rolling, laminar cooling and coiling.
In a preferred embodiment, the continuous casting step includes the steps of: molten iron pretreatment, converter combined blowing, RH refining and casting machine; specifically, carrying out desulfurization pretreatment on molten iron, carrying out decarburization and dephosphorization on the molten iron by adopting a top-bottom combined blown converter to obtain molten steel, and adding the obtained molten steel into the converter, wherein the tapping temperature of the converter is more than or equal to 1610 ℃; and then, carrying out an LF refining process on the molten steel smelted by the converter, and adding alloys such as ferromanganese, ferrosilicon, ferrocolumbium and the like according to the components of the molten steel to adjust the components to target components. And (3) carrying out RH operation on the molten steel after LF refining, adjusting the flow of argon to enable the molten steel to be in a soft blowing state after RH vacuum treatment is finished, feeding Si-Ca wires for calcium treatment, and ensuring that the soft blowing time is more than 5min after wire feeding to prevent the molten steel from being exposed.
In a preferred embodiment, in the continuous casting step, the molten steel contains the following chemical components in percentage by weight: . For example: c: 0.06%, Si: 0.20%, Mn: 1.60 percent, P is less than or equal to 0.017 percent, S is less than or equal to 0.002 percent, Alt: 0.050%, Ti: 0.085%, Nb: 0.045%, N: 0.0045 percent; or C: 0.08%, Si: 0.10%, Mn: 1.85 percent, less than or equal to 0.017 percent of P, less than or equal to 0.002 percent of S, Alt: 0.020%, Ti: 0.065%, Nb: 0.045%; n: 0.0035%, or C: 0.07%, Si: 0.15%, Mn: 1.75 percent, less than or equal to 0.017 percent of P, less than or equal to 0.002 percent of S, Alt: 0.030%, Ti: 0.070%, Nb: 0.050%, N: 0.0030%, etc. Micro Nb and Ti micro alloy elements are added in the steel making process, the strength is improved by combining the solid solution strengthening of the carbon and manganese elements and the fine crystal strengthening of the alloy elements, and the good stamping performance and welding performance are kept while the strength is improved, so that the good strength and plasticity balance is presented.
In a preferred embodiment, in the continuous casting billet heating step, the heating process is controlled in the furnace time of 200-260 min, and the discharging temperature of 1190-1230 ℃; for example, the furnace time is controlled to be 200min, 210min, 220min, 230min, 240min, 250min, 260min, etc.
In a preferred embodiment, in the rough rolling step, the rough rolling is rough rolling by using a 3+3 model 2-frame rolling mill, the rough rolling initial rolling temperature is 1120-1190 ℃, the rough rolling initial rolling reduction is 25.0-37.0 mm, such as 1120 ℃, 1130 ℃, 1140 ℃,1150 ℃, 1160 ℃, 1170 ℃, 1180 ℃,1190 ℃, and the like, such as the rough rolling initial rolling reduction is 25.0mm, 27.0mm, 29.0mm, 31.0mm, 33.0mm, 35.0mm, 37.0mm and the like.
In a preferred embodiment, in the finish rolling step, the finish rolling is performed by using a 7-stand continuous variable crown (cvc) rolling mill, and the start rolling temperature of the finish rolling is 950 to 1100 ℃, and the finish rolling temperature is 820 to 860 ℃, for example 820 ℃, 830 ℃, 840 ℃, 850 ℃, 860 ℃ and the like.
The invention adopts two-stage controlled rolling process of rough rolling and finish rolling, namely austenite recrystallization region rolling and austenite non-recrystallization region rolling, so that the steel can obtain a deformed austenite structure storing large deformation energy while finishing rolling, further obtain a fine phase change structure, and improve the strength of the steel through fine grain strengthening.
In a preferred embodiment, in order to ensure the grain size of 1/2 parts of the thick-gauge girder steel in the transverse direction, the thickness (mm) of the intermediate billet/the thickness (mm) of the finished product is 3.4-4.6, and the cumulative reduction rate of finish rolling is more than 70%.
In a preferred embodiment, in the cooling and coiling step, the cooling is laminar cooling, a front-stage cooling mode is adopted, and the cooling speed is 20-40 ℃/s, such as 20 ℃/s, 25 ℃/s, 30 ℃/s, 35 ℃/s, 40 ℃/s and the like; the coiling temperature is 590-610 ℃, such as 590 ℃, 600 ℃, 610 ℃ and the like.
Example 1: the preparation method of the automobile girder steel with the thickness of 12.0-16.0 mm and the high toughness of 700MPa
Carrying out desulfurization pretreatment on molten iron, adopting a top-bottom combined blown converter to carry out smelting to decarbonize and dephosphorize the molten iron to obtain molten steel, adding scrap steel into the converter, and enabling the tapping temperature of the converter to be more than or equal to 1610 ℃. And then, carrying out an LF refining process on the molten steel smelted by the converter, and adding alloys such as ferromanganese, ferrosilicon, ferrocolumbium and the like according to the components of the molten steel to adjust the components to target components. And (3) carrying out RH operation on the molten steel after LF refining, adjusting the flow of argon to enable the molten steel to be in a soft blowing state after RH vacuum treatment is finished, feeding Si-Ca wires for calcium treatment, and ensuring that the soft blowing time is more than 5min after wire feeding to prevent the molten steel from being exposed. Smelting according to the chemical components shown in the table 1, and continuously casting a plate blank with the superheat degree of 25 ℃. And then slab cleaning, slow cooling and continuous casting billet quality inspection are carried out. The heating temperature of the plate blank is 1210 ℃, the heating time is 210min, and the heated plate blank is subjected to high-pressure water dephosphorization. The width is fixed by a width fixing press, 2 frames are adopted for rough rolling, and 7 frames are adopted for CVC finish rolling. The initial rolling temperature of rough rolling is 1140 ℃, the initial rolling temperature of finish rolling is 970 ℃, the first pass reduction of rough rolling is 25.0mm, the thickness of an intermediate billet is 55.0mm, and the finish rolling temperature is 850 ℃. The laminar cooling adopts front-section cooling, the cooling speed is 25 ℃/s, the coiling temperature is 610 ℃, the thickness of a finished product is 12.0mm, and the thickness of an intermediate blank (mm)/the thickness of the finished product (mm) are as follows: 4.58. the results of the mechanical property measurements of the steel strip prepared in this example are shown in table 2.
Example 2: the preparation method of the automobile girder steel with the thickness of 12.0-16.0 mm and the high toughness of 700MPa
Carrying out desulfurization pretreatment on molten iron, adopting a top-bottom combined blown converter to carry out smelting to decarbonize and dephosphorize the molten iron to obtain molten steel, adding scrap steel into the converter, and enabling the tapping temperature of the converter to be more than or equal to 1610 ℃. And then, carrying out an LF refining process on the molten steel smelted by the converter, and adding alloys such as ferromanganese, ferrosilicon, ferrocolumbium and the like according to the components of the molten steel to adjust the components to target components. And (3) carrying out RH operation on the molten steel after LF refining, adjusting the flow of argon to enable the molten steel to be in a soft blowing state after RH vacuum treatment is finished, feeding Si-Ca wires for calcium treatment, and ensuring that the soft blowing time is more than 5min after wire feeding to prevent the molten steel from being exposed. Smelting according to the chemical components shown in the table 1, and continuously casting a plate blank with the superheat degree of 25 ℃. And then slab cleaning, slow cooling and continuous casting billet quality inspection are carried out. The heating temperature of the plate blank is 1200 ℃, the heating time is 230min, and the heated plate blank is subjected to high-pressure water dephosphorization. The width is fixed by a width fixing press, 2 frames are adopted for rough rolling, and 7 frames are adopted for CVC finish rolling. The initial rolling temperature of rough rolling is 1150 ℃, the initial rolling temperature of finish rolling is 960 ℃, the first reduction of rough rolling is 27.0mm, the thickness of the intermediate billet is 50.0mm, and the finish rolling temperature is 850 ℃. The laminar cooling adopts front-section cooling, the cooling speed is 30 ℃/s, the coiling temperature is 600 ℃, the thickness of a finished product is 14.0mm, and the thickness of an intermediate blank (mm)/the thickness of the finished product (mm) are as follows: 3.57. the results of the mechanical property measurements of the steel strips prepared in the examples are shown in Table 2.
Example 3: the preparation method of the automobile girder steel with the thickness of 12.0-16.0 mm and the high toughness of 700MPa
Carrying out desulfurization pretreatment on molten iron, adopting a top-bottom combined blown converter to carry out smelting to decarbonize and dephosphorize the molten iron to obtain molten steel, adding scrap steel into the converter, and enabling the tapping temperature of the converter to be more than or equal to 1610 ℃. And then, carrying out an LF refining process on the molten steel smelted by the converter, and adding alloys such as ferromanganese, ferrosilicon, ferrocolumbium and the like according to the components of the molten steel to adjust the components to target components. And (3) carrying out RH operation on the molten steel after LF refining, adjusting the flow of argon to enable the molten steel to be in a soft blowing state after RH vacuum treatment is finished, feeding Si-Ca wires for calcium treatment, and ensuring that the soft blowing time is more than 5min after wire feeding to prevent the molten steel from being exposed. Smelting according to the chemical components shown in the table 1, and continuously casting a plate blank with the superheat degree of 25 ℃. And then slab cleaning, slow cooling and continuous casting billet quality inspection are carried out. The heating temperature of the plate blank is 1220 ℃, the heating time is 255min, and the high-pressure water dephosphorization is carried out on the heated plate blank. The width is fixed by a width fixing press, 2 frames are adopted for rough rolling, and 7 frames are adopted for CVC finish rolling. The initial rolling temperature of rough rolling is 1190 ℃, the initial rolling temperature of finish rolling is 1000 ℃, the first-pass reduction of rough rolling is 35.0mm, the thickness of an intermediate billet is 55.0mm, and the finish rolling temperature is 840 ℃. The laminar cooling adopts front-section cooling, the cooling speed is 35 ℃/s, the coiling temperature is 590 ℃, the thickness of a finished product is 16.0mm, and the thickness of an intermediate blank (mm)/the thickness of the finished product (mm) are as follows: 3.44.
FIG. 1 is a typical microstructure diagram of a steel strip produced in this example, from which it can be seen that the microstructure is ferrite and a small amount of pearlite with a grain size of about grade 13. The results of the mechanical property measurements of the steel strip prepared in this example are shown in table 2.
Example 4: the preparation method of the automobile girder steel with the thickness of 12.0-16.0 mm and the high toughness of 700MPa
Carrying out desulfurization pretreatment on molten iron, adopting a top-bottom combined blown converter to carry out smelting to decarbonize and dephosphorize the molten iron to obtain molten steel, adding scrap steel into the converter, and enabling the tapping temperature of the converter to be more than or equal to 1610 ℃. And then, carrying out an LF refining process on the molten steel smelted by the converter, and adding alloys such as ferromanganese, ferrosilicon, ferrocolumbium and the like according to the components of the molten steel to adjust the components to target components. And (3) carrying out RH operation on the molten steel after LF refining, adjusting the flow of argon to enable the molten steel to be in a soft blowing state after RH vacuum treatment is finished, feeding Si-Ca wires for calcium treatment, and ensuring that the soft blowing time is more than 5min after wire feeding to prevent the molten steel from being exposed. Smelting according to the chemical components shown in the table 1, and continuously casting a plate blank with the superheat degree of 25 ℃. And then slab cleaning, slow cooling and continuous casting billet quality inspection are carried out. The heating temperature of the plate blank is 1230 ℃, the heating time is 200min, and the heated plate blank is subjected to high-pressure water dephosphorization. The width is fixed by a width fixing press, 2 frames are adopted for rough rolling, and 7 frames are adopted for CVC finish rolling. The initial rolling temperature of rough rolling is 1190 ℃, the initial rolling temperature of finish rolling is 1080 ℃, the first-pass reduction of rough rolling is 30.0mm, the thickness of an intermediate billet is 42.0mm, and the finish rolling temperature of finish rolling is 860 ℃. The laminar cooling adopts front-section cooling, the cooling speed is 25 ℃/s, the coiling temperature is 600 ℃, the thickness of a finished product is 12.0mm, and the thickness of an intermediate blank (mm)/the thickness of the finished product (mm) are as follows: 3.50. the results of the mechanical property measurements of the steel strips prepared in the examples are shown in Table 2.
Example 5: the preparation method of the automobile girder steel with the thickness of 12.0-16.0 mm and the high toughness of 700MPa
Carrying out desulfurization pretreatment on molten iron, adopting a top-bottom combined blown converter to carry out smelting to decarbonize and dephosphorize the molten iron to obtain molten steel, adding scrap steel into the converter, and enabling the tapping temperature of the converter to be more than or equal to 1610 ℃. And then, carrying out an LF refining process on the molten steel smelted by the converter, and adding alloys such as ferromanganese, ferrosilicon, ferrocolumbium and the like according to the components of the molten steel to adjust the components to target components. And (3) carrying out RH operation on the molten steel after LF refining, adjusting the flow of argon to enable the molten steel to be in a soft blowing state after RH vacuum treatment is finished, feeding Si-Ca wires for calcium treatment, and ensuring that the soft blowing time is more than 5min after wire feeding to prevent the molten steel from being exposed. Smelting according to the chemical components shown in the table 1, and continuously casting a plate blank with the superheat degree of 25 ℃. And then slab cleaning, slow cooling and continuous casting billet quality inspection are carried out. Heating the plate blank at 1200 ℃ for 240min, and removing phosphorus from the heated plate blank by high-pressure water. The width is fixed by a width fixing press, 2 frames are adopted for rough rolling, and 7 frames are adopted for CVC finish rolling. The initial rolling temperature of rough rolling is 1170 ℃, the initial rolling temperature of finish rolling is 1080 ℃, the first-pass reduction of rough rolling is 35.0mm, the thickness of an intermediate blank is 57.0mm, and the finish rolling temperature is 830 ℃. The laminar cooling adopts front-section cooling, the cooling speed is 40 ℃/s, the coiling temperature is 600 ℃, the thickness of a finished product is 16.0mm, and the thickness of an intermediate blank (mm)/the thickness of the finished product (mm) are as follows: 3.56. the results of the mechanical property measurements of the steel strip prepared in this example are shown in table 2.
TABLE 1 chemical composition of inventive examples 1-5 (wt%)
| Examples | C | Si | Mn | P | S | Alt | Nb | Ti | N |
| 1 | 0.07 | 0.15 | 1.68 | 0.013 | 0.003 | 0.037 | 0.050 | 0.080 | 0.0032 |
| 2 | 0.08 | 0.20 | 1.75 | 0.011 | 0.002 | 0.032 | 0.047 | 0.083 | 0.0029 |
| 3 | 0.08 | 0.25 | 1.80 | 0.012 | 0.002 | 0.038 | 0.052 | 0.080 | 0.0035 |
| 4 | 0.07 | 018 | 1.65 | 0.015 | 0.003 | 0.042 | 0.045 | 0.075 | 0.0030 |
| 5 | 0.08 | 0.21 | 1.75 | 0.0010 | 0.003 | 0.035 | 0.049 | 0.083 | 0.0034 |
TABLE 2 results of mechanical property measurements of steel strips prepared in examples 1 to 5 of the present invention
As can be seen from the data in Table 2, the automobile girder steel hot rolled steel strip with the thickness of 12.0-16.0 mm and the high toughness of 700MPa provided by the invention has the mechanical properties and the process properties that the yield strength is more than or equal to 620MPa, the tensile strength is more than or equal to 700MPa, the elongation A is more than or equal to 18%, and the cold bending d is 2a, and the longitudinal impact power KV2 is more than or equal to 70J at the temperature of minus 20 ℃.
From the results of the above examples, it can be seen that the steel strip for automobile frame of the present invention has excellent mechanical properties, especially low temperature toughness, and at the same time has good weldability.
The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.
Claims (7)
1. The automobile girder steel with the thickness of 12.0-16.0 mm and the high toughness of 700MPa is characterized by comprising the following chemical components in percentage by weight: 0.06-0.09%, Si: 0.10 to 0.30%, Mn: 1.60-1.90%, P is less than or equal to 0.020%, S is less than or equal to 0.005%, Alt: 0.020 to 0.050%, Nb: 0.04-0.06%, Ti: 0.06-0.10 percent of N, less than or equal to 0.0050 percent of N, and the balance of Fe and inevitable impurities.
2. The automobile girder steel with the thickness of 12.0-16.0 mm and the high toughness of 700MPa according to claim 1, wherein the chemical components of the girder steel are as follows by weight percent: 0.07 to 0.09%, Si: 0.15 to 0.25%, Mn: 1.70-1.85%, P is less than or equal to 0.015%, S is less than or equal to 0.003%, Alt: 0.030-0.045%, Nb: 0.045-0.055%, Ti: 0.065-0.90%, N is less than or equal to 0.0035%, and the balance is Fe and inevitable impurities.
3. The production method of the automobile beam steel with the thickness of 12.0-16.0 mm and the high toughness of 700MPa according to any one of claims 1-2, characterized by comprising the following steps of: the method comprises the following steps of molten iron pretreatment, converter combined blowing, RH refining, continuous casting, slab heating, hot continuous rolling, laminar cooling and coiling; the hot continuous rolling process comprises rough rolling and finish rolling;
wherein:
carrying out desulfurization pretreatment on molten iron, carrying out decarburization and dephosphorization on the molten iron by adopting a top-bottom combined blown converter to obtain molten steel, adding the obtained molten steel into the converter, wherein the tapping temperature of the converter is more than or equal to 1610 ℃; then, performing an LF refining process on the molten steel smelted by the converter, and adding ferromanganese, ferrosilicon and ferroniobium alloy according to the components of the molten steel to adjust to target components; RH operation is carried out on molten steel after LF refining, after RH vacuum treatment is finished, the argon flow is adjusted to enable the molten steel to be in a soft blowing state, Si-Ca wires are fed for calcium treatment, soft blowing time is guaranteed to be more than 5min after wire feeding, and the molten steel is prevented from being exposed;
when the plate blank is heated, the heating process is controlled to be 200-260 min, and the discharging temperature is 1190-1230 ℃;
the rough rolling is carried out by adopting a 3+3 mode 2-frame rolling mill, the initial rolling temperature of the rough rolling is 1120-1190 ℃, and the first-pass reduction of the rough rolling is 25.0-37.0 mm;
the finish rolling is carried out by adopting a 7-frame continuous variable-crown rolling mill, wherein the start rolling temperature of the finish rolling is 950-1100 ℃, the thickness of an intermediate blank during the start rolling of the finish rolling is 3.4-4.6 times of the thickness of a finished steel plate, the cumulative reduction rate of the finish rolling is more than 70%, and the finish rolling temperature is 820-860 ℃;
the laminar cooling adopts a front section cooling mode, the cooling speed is 20-40 ℃/s, and the coiling temperature is 590-610 ℃.
4. The production method according to claim 3, wherein the heating process is controlled in a furnace time of 200min, 210min, 220min, 230min, 240min, 250min or 260 min.
5. The production method according to claim 3, wherein the rough rolling first pass reduction is 25.0mm, 27.0mm, 29.0mm, 31.0mm, 33.0mm, 35.0mm, or 37.0 mm.
6. The production method according to claim 3, wherein the rough rolling start temperature is 1120 ℃, 1130 ℃, 1140 ℃,1150 ℃, 1160 ℃, 1170 ℃, 1180 ℃ or 1190 ℃.
7. The production method according to claim 3, wherein the finish rolling temperature is 820 ℃, 830 ℃, 840 ℃, 850 ℃ or 860 ℃.
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