阅读说明：本技术 一种通过薄板坯连铸连轧生产汽车大梁板的方法 (Method for producing automobile girder plate by thin slab continuous casting and rolling ) 是由 戴杰涛 沈健 于 2020-07-15 设计创作，主要内容包括：本发明公开了一种通过薄板坯连铸连轧生产汽车大梁板的方法,通过采用薄板坯连铸连轧工艺生产汽车大梁板,生产工艺包括：铁水冶炼、连铸、热轧,精整,具体生产步骤包括：高温炉熔化铁水→铁水预处理→转炉冶炼→精炼→薄板坯连铸→均热→轧制→层流冷切→卷取→检查→打包入库。本发明的通过薄板坯连铸连轧生产汽车大梁板的方法可以生产出符合要求的汽车大梁板,并解决普通大梁板碳含量较高,加工性能和焊接性能较差的问题。另外,本发明通过合理的合金化设计,采用V、Nb、Ti复合微合金化技术,充分利用V、Nb、Ti微合金元素的细晶强化、析出强化等强化机理能有效提高汽车大梁板的综合机械性能。(The invention discloses a method for producing an automobile girder plate by thin slab continuous casting and rolling, which adopts a thin slab continuous casting and rolling process to produce the automobile girder plate, and the production process comprises the following steps: smelting molten iron, continuous casting, hot rolling and finishing, and the specific production steps comprise: molten iron in a high-temperature furnace → molten iron pretreatment → converter smelting → refining → thin slab continuous casting → soaking → rolling → laminar flow cold cutting → coiling → inspection → packaging and warehousing. The method for producing the automobile girder plate by the thin slab continuous casting and rolling can produce the automobile girder plate meeting the requirements and solve the problems of high carbon content, poor processing performance and poor welding performance of the common girder plate. In addition, the invention can effectively improve the comprehensive mechanical property of the automobile girder plate by reasonable alloying design and by adopting a V, Nb and Ti composite micro-alloying technology and fully utilizing strengthening mechanisms of fine grain strengthening, precipitation strengthening and the like of V, Nb and Ti micro-alloy elements.)

1. A method for producing an automobile girder plate by continuous casting and rolling of a thin slab is characterized by sequentially comprising the following steps: molten iron in a high-temperature furnace → molten iron pretreatment → converter smelting → refining → thin slab continuous casting → soaking → hot continuous rolling unit rolling → laminar cooling → coiling → inspection → packaging and warehousing; wherein the content of the first and second substances,

in the process of melting molten iron in a high-temperature furnace, melting a thin slab into high-temperature molten iron through a high-temperature smelting furnace;

in the molten iron pretreatment process, firstly carrying out slag skimming on high-temperature molten iron, then carrying out blowing passivation magnesium desulfurization, and then carrying out slag skimming, wherein the slag skimming rate is more than or equal to 92%; ensuring that the final [ S ] of the high-temperature molten iron is 0.0010%; in the molten iron pretreatment process, an argon blowing process is adopted in the whole process, and the alkalinity of the final slag is 3.5;

in the smelting process of the converter, top-bottom combined blowing operation is adopted, argon blowing technology is adopted in the whole process, strict control is carried out on [ C ], [ P ] and [ S ] at the end point of the converter, the [ C ] at the end point of the converter is ensured to be less than or equal to 0.040%, and the [ P ] at the end point of the converter is ensured to be less than or equal to 0.015%;

in the refining process, firstly stirring the high-temperature molten iron smelted in the converter for 1-2 min by argon with the flow rate of 500-600NL/min so as to facilitate slagging; the argon blowing flow is kept at 200-300NL/min during power transmission and temperature rise; the argon blowing flow is increased during desulfurization; the exposed diameter of the slag surface is less than 100mm during soft blowing, the soft blowing time is more than 6min, and the [ S ] at the refining end point is ensured to be less than 0.01%;

in the process of continuously casting the thin slab, the superheat degree of the tundish molten iron is controlled at 20-40 ℃, and the drawing speed is controlled at 3.7-4.0 m/min;

in the soaking process, the continuous casting blank is sent into a heating furnace to be heated, the heating time in the heating furnace is more than or equal to 60min, the charging temperature of the continuous casting blank is more than or equal to 1000 ℃, the heating temperature is more than or equal to 1150 ℃, and the temperature of the slab discharged from the heating furnace is 1120-1150 ℃;

in the rolling process of the hot continuous rolling unit, the continuous casting slab is firstly sent into a hot continuous rolling 5-7 rack finishing rolling unit, the reduction rate of the first two times of finish rolling is more than or equal to 50 percent, and the reduction rate of the subsequent times of finish rolling is less than or equal to 15 percent; the outlet temperature of the finish rolling is kept at 860 ℃ and 880 ℃; then carrying out laminar cooling on the rolled piece;

and in the coiling process, the rolled piece subjected to laminar cooling is coiled by a coiling machine, the coiling temperature is 600-620 ℃, and leveling and finishing are carried out on a leveling unit.

2. The method for manufacturing an automobile girder according to claim 1, wherein the refining process includes RH furnace refining and LF furnace refining, wherein N is controlled to 50ppm or less and O is controlled to 35ppm or less during the LF furnace refining.

3. The method for manufacturing an automobile girder according to claim 1, wherein the Al in the molten iron is changed by a Ca treatment process after the completion of refining₂O₃According to the property of the inclusion, a specific amount of Ca wire is fed according to the Al content in the high-temperature molten iron, and the Ca/Al is ensured to be more than or equal to 0.1; ensuring soft argon blowing time after Ca treatment>6min。

4. The method for producing the automobile girder according to claim 1, wherein after the soaking process, the continuous casting slab is subjected to dephosphorization with high pressure water under dephosphorization pressure not lower than 16MPa, and the dephosphorization enters a finishing mill set with a hot continuous rolling stand of 5-7 after dephosphorization.

5. The method for producing an automobile girder according to claim 1, wherein the ratio of each element is: 0.03-0.07 wt% of C, 0.2-0.35 wt% of Si, 1.2-1.5 wt% of Mn, 0.02-0.06 wt% of Nb, 0.015-0.04 wt% of Ti, 0.04-0.06 wt% of V, less than 0.015 wt% of P, less than 0.010 wt% of S and the balance Fe.

Technical Field

The invention relates to a method for manufacturing an automobile, in particular to a method for producing an automobile girder plate by thin slab continuous casting and rolling.

Background

Automotive frame steel is required to have high strength, high plasticity and toughness, low ductile-brittle transition temperature, good welding performance and particularly excellent stamping performance. In the past, the most widely used automobile beam steel in China is 09SiTi, 09MnReL, 16MnL, 16MnReL and the like, the yield strength is 250-.

The hot metal metallurgy process, the metallurgical solidification process characteristics and the phase change characteristics of the materials of the thin slab continuous casting and rolling are greatly different from those of the thick slab continuous casting and rolling process, and the method is very suitable for producing microalloy high-strength steel with the yield strength of 350-600 MPa. On a CSP production line, the component design of low-carbon composite micro alloy (V, Nb and Ti) is adopted, and the rolling and cooling control process is matched, so that common carbon steel or low alloy steel can become high-strength steel with higher added value. The microalloying rolling and cooling control process has the following functions:

(1) the method is favorable for obtaining fine austenite microstructure and forming fine ferrite during phase transformation;

(2) controlling the hot rolling process to repeatedly recrystallize the steel between deformation passes to finish austenite refining;

(3) nb and Ti elements are combined with N in steel to form fine and dispersed NbN and TiN pinning grain boundaries to prevent austenite grains from growing;

(4) controlling the cooling speed to promote a large amount of ferrite nucleation to further refine the grains;

(5) v has the functions of grain refinement and precipitation strengthening, has low sensitivity to transverse cracks in the continuous casting process, and is beneficial to recrystallization of coarse cast austenite grains during hot rolling.

Based on the advantages, the invention provides a production method for producing the automobile girder plate by thin slab continuous casting and rolling.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a method for producing the automobile girder plate by thin slab continuous casting and rolling.

The technical scheme for solving the technical problems is as follows:

a method for producing an automobile girder plate by thin slab continuous casting and rolling sequentially comprises the following steps: molten iron in a high-temperature furnace → molten iron pretreatment → converter smelting → refining → thin slab continuous casting → soaking → hot continuous rolling unit rolling → laminar cooling → coiling → inspection → packaging and warehousing; wherein the content of the first and second substances,

in the process of melting molten iron in a high-temperature furnace, melting a thin slab into the high-temperature molten iron by the high-temperature smelting furnace, wherein the temperature of the high-temperature molten iron is 1255 ℃, and [ S ] is 0.019%;

in the molten iron pretreatment process, firstly slagging off high-temperature molten iron, then spraying passivated magnesium for desulfurization, and then slagging off, wherein the slagging off rate is more than or equal to 92%; ensuring that the final [ S ] of the high-temperature molten iron is 0.0010%; in the molten iron pretreatment process, an argon blowing process is adopted in the whole process, and the alkalinity of the final slag is 3.5;

in the smelting process of the converter, top-bottom combined blowing operation is adopted, argon blowing technology is adopted in the whole process, strict control is carried out on [ C ], [ P ] and [ S ] at the end point of the converter, the [ C ] at the end point of the converter is ensured to be less than or equal to 0.040%, and the [ P ] at the end point of the converter is ensured to be less than or equal to 0.015%;

in the refining process, firstly stirring the high-temperature molten iron smelted in the converter for 1-2 min by argon with the flow rate of 500-600NL/min so as to facilitate slagging; the argon blowing flow is kept at 200-300NL/min during power transmission and temperature rise; the argon blowing flow is increased during desulfurization; the exposed diameter of the slag surface is less than 100mm during soft blowing, the soft blowing time is more than 6min, and the [ S ] at the refining end point is ensured to be less than 0.01%;

in the process of continuously casting the thin slab, the superheat degree of the tundish molten iron is controlled at 20-40 ℃, and the drawing speed is controlled at 3.7-4.0 m/min;

in the soaking process, the continuous casting blank is sent into a heating furnace to be heated, the heating time in the heating furnace is more than or equal to 60min, the charging temperature of the continuous casting blank is more than or equal to 1000 ℃, the heating temperature is more than or equal to 1150 ℃, and the temperature of the slab discharged from the heating furnace is 1120-1150 ℃;

in the rolling process of the hot continuous rolling unit, the continuous casting slab is firstly sent into a hot continuous rolling 5-7 rack finishing rolling unit, the reduction rate of the first two times of finish rolling is more than or equal to 50 percent, and the reduction rate of the subsequent times of finish rolling is less than or equal to 15 percent; the outlet temperature of the finish rolling is kept at 860 ℃ and 880 ℃; then carrying out laminar cooling on the rolled piece;

and in the coiling process, the rolled piece subjected to laminar cooling is coiled by a coiling machine, the coiling temperature is 600-620 ℃, and leveling and finishing are carried out on a leveling unit.

Preferably, the refining process comprises RH furnace refining and LF furnace refining, wherein N is controlled below 50ppm and O is controlled below 35ppm in the LF furnace refining process.

Preferably, after the refining is finished, a Ca treatment process is adopted to change Al in the molten iron₂O₃According to the property of the inclusion, a specific amount of Ca wire is fed according to the Al content in the high-temperature molten iron, and the Ca/Al is ensured to be more than or equal to 0.1; ensuring soft argon blowing time after Ca treatment>6min。

Preferably, after the soaking process, high-pressure water dephosphorization is carried out on the continuous casting slab, the dephosphorization pressure is more than or equal to 16MPa, and the dephosphorization enters a hot continuous rolling 5-7 stand finishing mill group.

Preferably, the ratio of each element in the thin slab is as follows: 0.03-0.07 wt% of C, 0.2-0.35 wt% of Si, 1.2-1.5 wt% of Mn, 0.02-0.06 wt% of Nb, 0.015-0.04 wt% of Ti, 0.04-0.06 wt% of V, less than 0.015 wt% of P, less than 0.010 wt% of S and the balance Fe.

Compared with the prior art, the invention has the following beneficial effects:

1. in the invention, through the production process flow of converter steelmaking (BOF), refining (LF) and thin slab continuous casting and rolling (CSP), a low-carbon microalloy and rolling-controlled cooling process is adopted, and the means of precipitation strengthening, fine grain strengthening, solid solution strengthening, dislocation strengthening and the like are fully utilized to realize large-scale production of 510L and 590L girder steel coils, so that a low-cost production process technology of high-strength steel is formed, and the domestic first-class level of producing automotive girder steel by thin slab continuous casting and rolling is reached.

2. According to the invention, through reasonable alloying design, a V, Nb and Ti composite micro-alloying technology is adopted, and strengthening mechanisms of fine grain strengthening, precipitation strengthening and the like of V, Nb and Ti micro-alloy elements are fully utilized, so that the comprehensive mechanical properties of the steel can be effectively improved. The controlled rolling and controlled cooling process for girder steel production is optimized, and the micro-alloy element effect can be exerted to the maximum extent. In the development process, parameters such as finish rolling and coiling temperature are optimized for different microalloy addition amounts, so that the strength can be effectively improved, the good toughness and plasticity are ensured, social resources are saved, and the production cost is reduced.

Drawings

FIG. 1 is a process flow diagram of the production method of the present invention for producing an automobile girder slab by continuous casting and rolling of a thin slab.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.

Referring to fig. 1, the method for manufacturing an automobile girder according to the present invention by continuous casting and rolling of a thin slab includes the steps of: molten iron in a high-temperature furnace → molten iron pretreatment → converter smelting → refining → thin slab continuous casting → soaking → hot continuous rolling unit rolling → laminar cooling → coiling → inspection → packaging and warehousing;

wherein, in the process of melting molten iron in a high-temperature furnace, a sheet billet is melted into the high-temperature molten iron through a high-temperature smelting furnace, wherein the temperature of the high-temperature molten iron is 1255 ℃, and [ S ] is 0.019%;

in the molten iron pretreatment process, firstly slagging off high-temperature molten iron, then spraying passivated magnesium for desulfurization, and then slagging off, wherein the slagging off rate is more than or equal to 92%; ensuring that the final [ S ] of the high-temperature molten iron is 0.0010%; in the molten iron pretreatment process, an argon blowing process is adopted in the whole process, and the alkalinity of the final slag is 3.5;

in the smelting process of the converter, top-bottom combined blowing operation is adopted, an argon blowing process is adopted in the whole process, good bottom blowing stirring is ensured, strict control is carried out on [ C ], [ P ] and [ S ] at the end point of the converter, and the end point of the converter is ensured to be less than or equal to 0.040 percent, so that the content of C in the upper molten iron can be ensured to be less than 0.07 percent even if C is increased in the refining process; ensuring that the P content at the end point of the converter is less than or equal to 0.015 percent, fully removing P before tapping of the converter in order to ensure that the finished product has lower P content, and ensuring that the P content control meets the requirement by adopting measures of slagging in advance, slagging well and the like.

In the refining process, the refining process comprises RH furnace refining and LF furnace refining, and the method comprises the following specific steps: firstly, stirring the high-temperature molten iron smelted in the converter for 1-2 min by argon with the flow rate of 500-600NL/min so as to dissolve slag; the argon blowing flow is kept at 200-300NL/min during power transmission and temperature rise; the argon blowing flow is increased during desulfurization; the exposed diameter of the slag surface is less than 100mm during soft blowing, the soft blowing time is more than 6min, and the [ S ] at the refining end point is ensured to be less than 0.01%; n is controlled to be below 50ppm and O is controlled to be below 35ppm in the refining process of the LF furnace. The method comprises the steps of firstly, reducing the oxidability of high-temperature molten iron by adding aluminum particles for deoxidation, controlling the temperature to be about 1600 ℃ so as to facilitate desulfurization, then increasing argon gas for stirring so as to increase the steel-slag interface reaction, and accelerating the desulfurization speed. Controlling Als in the high-temperature molten iron to stabilize the content of [ O ] in the molten iron so as to ensure that the Ti component is relatively stable.

After refining is finished, a Ca treatment process is adopted to change Al in the molten iron₂O₃According to the property of the inclusion, a certain amount of Ca wires are fed according to the Al content in the high-temperature molten iron, so that the Ca/Al is more than or equal to 0.1, and solid fine Al is ensured₂O₃The impurities are changed into liquid calcium aluminate with low melting point, which is beneficial to gathering and floating. Ensuring sufficient after Ca treatmentAnd (3) soft argon blowing time (more than 6min) promotes most of liquid calcium aluminate inclusion to float upwards.

In the process of continuous casting of thin slabs, firstly, the continuous casting temperature is controlled, the superheat degree of tundish molten iron is controlled to be 20-40 ℃, and the superheat degree is lower than 15 ℃ or higher than 50 ℃ so as to be not beneficial to continuous casting stability or cause casting blank defects. And secondly, selecting a cooling curve and a vibration curve, wherein the cooling curve is generally adjusted according to the pulling speed and the temperature of molten iron, and the vibration curve is selected according to the negative slip time, the negative slip rate and the depth of the vibration mark. And finally, controlling the pulling speed stably by 3.7-4.0 m/min, keeping the pulling speed stable, facilitating the stable liquid level of the molten iron in the crystallizer, preventing slag entrapment and keeping the cleanliness of the molten iron. Finally, the quality of the middle package coating is improved; selecting mold flux with proper performance; avoiding the severe fluctuation of the liquid level; the SEN defect occurs and the use is stopped; ensuring the purity of molten iron and protecting casting in the whole process. The proper Ca/Al ratio is controlled, and the phenomenon of water blockage is reduced. Electromagnetic braking is adopted, and slag entrapment of molten iron is reduced.

In the soaking process, the continuous casting blank is sent into a heating furnace to be heated, the heating time in the heating furnace is more than or equal to 60min, the charging temperature of the continuous casting blank is more than or equal to 1000 ℃, the heating temperature is more than or equal to 1150 ℃, and the temperature of the slab discharged from the heating furnace is 1120-1150 ℃; after the soaking process, high-pressure water dephosphorization is carried out on the continuous casting billet, the dephosphorization pressure is not less than 16MPa, and the dephosphorization enters a hot continuous rolling 5-7 rack finishing mill group for rolling.

In the rolling process of the hot continuous rolling mill set, the reduction rate of the finish rolling of the first two times is more than or equal to 50 percent, the reduction rate of the finish rolling of the subsequent passes is less than or equal to 15 percent so as to ensure the accurate thickness and good plate shape, and the temperature of the finish rolling outlet is kept at 860-880 ℃; then carrying out laminar cooling on the rolled piece;

in the coiling process, the rolled piece subjected to laminar cooling is coiled by a coiling machine at the coiling temperature of 600-620 ℃ and is subjected to leveling and finishing in a leveling unit.

The thin slab in this embodiment has the following elements: 0.03-0.07 wt% of C, 0.2-0.35 wt% of Si, 1.2-1.5 wt% of Mn, 0.02-0.06 wt% of Nb, 0.015-0.04 wt% of Ti, 0.04-0.06 wt% of V, less than 0.015 wt% of P, less than 0.010 wt% of S and the balance Fe.

The method for producing the automobile girder plate by the thin slab continuous casting and rolling of the invention is explained by taking a specific production process as an example as follows:

firstly, putting the thin slab into a high-temperature furnace for melting, and then, controlling the temperature of molten iron after melting to be 1255 ℃, [ S ]]Firstly, carrying out slagging-off treatment on 0.019% of qualified molten iron; then spraying passivated magnesium for desulfurization, slagging off after the spraying is finished, wherein the slagging-off rate is more than or equal to 92 percent, and the [ S ] at the end point of the molten iron]0.0010 percent, adopts the whole argon blowing process, and has the final slag alkalinity of 3.5. The converter smelting process adopts top-bottom combined blowing operation, the bottom blowing and stirring are ensured to be good by blowing Ar in the whole process, the C content is 0.02 percent and the P content is 0.012 percent when the converter taps. Bottom blowing argon is adopted in the whole refining process. After molten iron of the converter enters the station, firstly stirring for 2min by argon with the flow rate of 500 plus 600 NL/min; the argon blowing flow should be kept at 250NL/min when the power is supplied and the temperature is raised; the exposed diameter of the slag surface is less than 80mm during soft blowing, and the soft blowing time is 6 min. N is controlled to 50ppm or less, and O is controlled to 35ppm or less. Controlling Als in molten iron to stabilize [ O ] in molten iron]Thereby ensuring that the Ti component is relatively stable. After refining, Ca treatment process is adopted to change Al in molten iron₂O₃According to the property of the inclusion, a certain amount of Ca lines are fed according to the Al content of the molten iron, so that the Ca/Al is more than or equal to 0.1. The superheat degree is controlled at 30 ℃, the continuous casting is put into a crystallizer for electromagnetic stirring in the continuous casting process, a continuous casting soft reduction process is adopted in a sector section, the continuous casting drawing speed is controlled at 3.8m/min, the thickness of a continuous casting blank is 70mm, the temperature of the continuous casting blank in a heating furnace is 1020 ℃, the heating time in the heating furnace is 62min, the heating temperature is 1180 ℃, the temperature of a slab-out heating furnace is 1130 ℃, high-pressure water dephosphorization is carried out, the front section of dephosphorization pressure is 20MPa, the rear end of dephosphorization is 24MPa, the dephosphorization enters a hot continuous rolling mill 5 rack finishing mill set, the rolling reduction of the first 2 finishing passes is respectively 55.2% and 53.4%, the rolling reduction of the last pass is 11.2%, the outlet thickness of a rolling mill is 8mm, the temperature of a finishing outlet is 870 ℃, and after a rolled piece is rolled, laminar cooling is adopted. The yield strength is 555MPa, the tensile strength is 625MPa, A₅₀The elongation is 28.3 percent, the surface Brinell hardness is 402HBW, the Charpy V-shaped impact energy is 92J, 85J and 82J respectively under the condition of-20 ℃, and the performance of the material meets 590L national standard GB/T24186 technical conditions of 2009.

The above description is a preferred embodiment of the present invention, but the present invention is not limited to the above description, and any other changes, modifications, substitutions, blocks and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and they are included in the scope of the present invention.