阅读说明：本技术 汽车板用无屈服平台的热镀锌低合金高强钢的生产方法 (Production method of hot-dip galvanized low-alloy high-strength steel without yield platform for automobile plate ) 是由 康华伟 高兴昌 张磊 尹翠兰 王鹏 侯晓英 于 2019-10-18 设计创作，主要内容包括：本发明涉及一种汽车板用无屈服平台的热镀锌低合金高强钢的生产方法,包括冶炼、连铸、热轧、酸连轧、热镀锌工序,钢的化学成分组成及质量百分含量为：C：0.060～0.090％,Si≤0.05％,Mn：0.65～0.75％,P：0.015～0.025％,S≤0.010％,Als：0.025～0.06％,Nb：0.025～0.035％,N≤0.0040％,其余为Fe和不可避免的杂质。通过合理的成分设计与热轧卷取温度、光整延伸率等关键工艺参数的控制,使位错摆脱溶质原子(柯氏气团)“钉锚”的作用,可完全消除屈服平台,避免再加工成形过程中产生的滑移线缺陷,提高产品最终表面质量,且具有优良的力学性能。(The invention relates to a production method of hot-dip galvanized low-alloy high-strength steel without a yield platform for an automobile plate, which comprises the following working procedures of smelting, continuous casting, hot rolling, acid continuous rolling and hot-dip galvanizing, wherein the steel comprises the following chemical components in percentage by mass: c: 0.060 to 0.090%, Si is not more than 0.05%, Mn: 0.65-0.75%, P: 0.015-0.025%, S is less than or equal to 0.010%, Als: 0.025 to 0.06%, Nb: 0.025-0.035%, N is less than or equal to 0.0040%, and the balance is Fe and inevitable impurities. Through reasonable component design and control of key process parameters such as hot rolling coiling temperature, finishing elongation and the like, dislocation gets rid of the action of solute atoms (Coriolis gas mass) "nail anchors", a yield platform can be completely eliminated, the defect of a slip line generated in the reprocessing and forming process is avoided, the final surface quality of a product is improved, and the product has excellent mechanical properties.)

1. The production method of the hot galvanizing low-alloy high-strength steel without the yield platform for the automobile plate is characterized by comprising the working procedures of smelting, continuous casting, hot rolling, acid continuous rolling and hot galvanizing, wherein the steel comprises the following chemical components in percentage by mass: c: 0.060 to 0.090%, Si is not more than 0.05%, Mn: 0.65-0.75%, P: 0.015-0.025%, S is less than or equal to 0.010%, Als: 0.025 to 0.06%, Nb: 0.025-0.035%, N is less than or equal to 0.0040%, and the balance is Fe and inevitable impurities.

2. The method for producing hot-dip galvanized low-alloy high-strength steel without yield plateau for automobile sheet according to claim 1, wherein the steel has a thickness specification of 0.5 to 2.5mm and a width specification of 900 to 1850 mm.

3. The method for producing hot-dip galvanized low-alloy high-strength steel without yield plateau for automobile sheet according to claim 1, wherein the yield strength of the steel is equal to or greater than 350MPa, the tensile strength is equal to or greater than 450MPa, the elongation A80 is equal to or greater than 25%, and the tensile curve has no yield plateau.

4. The method for producing hot-dip galvanized low-alloy high-strength steel without a yield plateau for automobile sheets according to claim 1, wherein the hot rolling finish rolling exit temperature in the hot rolling process is 890 ± 15 ℃, the cooling mode adopts front-stage laminar cooling, and the coiling temperature is 590 ± 15 ℃.

5. The method for producing the hot-dip galvanized low-alloy high-strength steel without a yield platform for the automobile sheet according to claim 1, wherein the total reduction rate of the acid continuous rolling is 58-78%.

6. The method for producing the hot-dip galvanized low-alloy high-strength steel without the yield platform for the automobile sheet as claimed in claim 1, wherein the annealing soaking temperature of the hot-dip galvanized low-alloy high-strength steel is 780 ± 10 ℃, the elongation of the finisher is 1.2-1.7%, the finishing rolling force is 3000-8000 KN, the roll diameter of the working roll of the finisher is phi 630-650 mm, the roughness of the working roll of the finisher is 2.0-2.5 μm, the speed of the finisher is 80-130mpm, and the elongation of the tension leveler is 0.2%.

Technical Field

The invention belongs to the technical field of metallurgy, and particularly relates to a production method of yield-platform-free hot-galvanized low-alloy high-strength steel HX340LAD + Z for an automobile plate.

Background

With the rapid development of automobile lightweight and the improvement of environmental protection requirements, the hot-dip galvanized low-alloy high-strength steel can reduce the thickness of a steel strip due to high strength so as to realize lightweight, and the corrosion resistance of a galvanized zinc layer is good so as to prolong the service life, so that the hot-dip galvanized low-alloy high-strength steel is more and more widely applied.

At present, most of produced hot-galvanized low-alloy high-strength steels have yield platforms with different degrees on stress-strain curves when tensile tests are carried out after annealing and galvanizing, and the yield platforms often generate slip lines (orange peels) during reprocessing and forming, so that the stamping forming capability is reduced, and the surface quality after processing is poor. For hot-galvanized low-alloy high-strength steel with a longer yield platform, the surface of the hot-galvanized low-alloy high-strength steel after being processed and formed has the defect of being similar to orange peel grains with obvious hand feeling, and the surface quality requirements of the inner plate and the outer plate of the automobile cannot be met.

CN 103469065A discloses a 340MPa grade HSLA steel for automobile structure and a production method thereof, and the steel comprises the following chemical components by mass percent: c: 0.06-0.07%, Mn: 0.5-0.65%, Si is less than or equal to 0.025%, P: 0.015-0.025%, S is less than or equal to 0.010%, Als: 0.03-0.05%, N: 0.0010-0.0040%, Nb: 0.025-0.035%, O is less than or equal to 0.006%, and the balance of Fe and inevitable impurities. The hot rolling heating temperature is 1200 +/-30 ℃, the finishing temperature is 900 +/-20 ℃, the coiling temperature is 600 +/-20 ℃, the cold rolling reduction is 70-75%, the cover annealing temperature is 670 +/-10 ℃, and the flattening elongation is 0.8%. The cover annealing furnace is adopted to produce 340 MPa-grade low-alloy high-strength steel, and the surface of a steel strip produced by cover annealing is relatively poor in continuous annealing.

CN104250703A discloses a 340 MPa-grade cold-rolled low-alloy high-strength steel and a manufacturing method thereof. The weight percentage of the chemical components is as follows: c: 0.03-0.06%, Si is less than or equal to 0.020%, Mn: 0.075-0.095%, P is less than or equal to 0.015%, S is less than or equal to 0.015%, Als: 0.015-0.045%, less than or equal to 0.10% of Ti and Nb, and the balance of Fe and inevitable trace elements. The process flow is as follows: blast furnace molten iron smelting → molten iron desulphurization pretreatment → converter molten steel smelting → LF molten steel refining treatment → CSP thin slab continuous casting and rolling → acid pickling cold continuous rolling → bell type furnace annealing → leveling → inspection and packaging for warehousing. The adopted CSP thin slab continuous casting and rolling and the bell-type annealing furnace produce 340 MPa-grade cold-rolled low-alloy high-strength steel, and the rolling reduction rate and the surface quality of the acid rolling cannot be ensured.

CN104399781A discloses a method for eliminating yield plateau of low-alloy high-strength steel. The method is implemented in the leveling and extending stage of the overall production process of the low-alloy high-strength steel, and the specific technical means is as follows: 1) setting tension set values of front and rear tension rollers of the temper mill to be 65-70N/mm 2; 2) using a leveling machine working roller with the diameter of 420-435 mm; 3) roughening the surface of the working roll of the temper mill in a capacitance mode; 4) the surface of a working roll of the leveling machine is roughened by selecting roughness with the numerical value of 3.3-3.7 mu m; 5) the process speed of the unit is set to be 140-160 m/min. The method can solve the problem of yield platform by improving the flat elongation of the low-alloy high-strength steel product, and can be widely applied to the technical field of automobile plate processing. However, only the technological parameters of the temper mill, such as tension, roll diameter, roughness, speed and the like, are described, and the steel-making components and the technological parameters of hot rolling, annealing and the like are not described.

CN104988389A discloses alloying hot-dip galvanized steel for automobiles with tensile strength of 340MPa and a production method thereof. The components and wt% thereof are: c: 0.06-0.10%, Si: less than or equal to 0.03 percent, Mn: 0.40-0.55%, P: 0.010-0.025%, S is less than or equal to 0.008%, Als: 0.020-0.070%; the production steps are as follows: pretreating molten iron; smelting in a converter and treating in an RH furnace; continuous casting; heating a casting blank; hot rolling; coiling; acid washing; cold rolling; continuous annealing; hot galvanizing; alloying; and (6) finishing. The alloyed hot-dip galvanized steel disclosed in CN104988389A, with the tensile strength of 340MPa, has the yield strength of only 250-280 MPa and the strength level is not high.

CN105239002A discloses a 340MPa grade continuous annealing cold rolling automobile structure steel plate and a production method thereof. The chemical components of the material by weight percentage are as follows: c is less than or equal to 0.0040, Si: 0 to 0.05, Mn: 0.25 to 0.45, Nb: 0.030 to 0.050, Ti: 0.010-0.030, N: 0.002 ~ 0.006, P: 0.04 to 0.07, S: 0-0.015, Als: 0.015-0.050, and the balance of Fe. The CN105239002A invention belongs to ultra-low carbon series continuous annealing cold rolling automobile structural steel with tensile strength of 340MPa grade, and has low yield strength, higher alloy content and higher production cost.

Disclosure of Invention

The invention aims to provide a method for producing hot-galvanized low-alloy high-strength steel HX340LAD + Z without yield platform for an automobile plate.

The technical scheme adopted by the invention for solving the technical problems is as follows: the production method of the hot galvanizing low-alloy high-strength steel without the yield platform for the automobile plate comprises the working procedures of smelting, continuous casting, hot rolling, acid continuous rolling and hot galvanizing, and the steel comprises the following chemical components in percentage by mass: c: 0.060 to 0.090%, Si is not more than 0.05%, Mn: 0.65-0.75%, P: 0.015-0.025%, S is less than or equal to 0.010%, Als: 0.025 to 0.06%, Nb: 0.025-0.035%, N is less than or equal to 0.0040%, and the balance is Fe and inevitable impurities.

The thickness specification of the steel is 0.5-2.5 mm, the width specification is 900-1850 mm, the yield strength is not less than 350MPa, the tensile strength is not less than 450MPa, the elongation A80 is not less than 25%, and a tensile curve has no yield platform.

Specifically, in the hot rolling procedure, the outlet temperature of hot rolling finish rolling is 890 +/-15 ℃, the cooling mode adopts front-stage laminar cooling, the coiling temperature is 590 +/-15 ℃, and the head and tail of the U-shaped coiling mode are 30 ℃ higher than the tail of the U-shaped coiling mode.

Specifically, the total reduction rate of the acid continuous rolling is 58-78%.

Specifically, the annealing soaking temperature of the hot galvanizing is 780 +/-10 ℃, the elongation of a finishing machine is 1.2-1.7%, the finishing rolling force is 3000-8000 KN, the roll diameter of a working roll of the finishing machine is phi 630-650 mm, the roughness of the working roll of the finishing machine is 2.0-2.5 mu m, the speed of the finishing machine is 80-130mpm, and the elongation of a tension leveler is 0.2%.

The detection method of the hot-dip galvanized low-alloy high-strength steel HX340LAD + Z hot-dip galvanized steel strip refers to GB/T228.

According to the manufacturing method of the hot-dip galvanized low-alloy high-strength steel without the yield platform, provided by the invention, on the premise of ensuring the precipitation strengthening effect of Nb (CN), the CN atom content is reduced as much as possible, the 'nail anchor' effect of carbon-nitrogen atom gas clusters (Cocker gas clusters) is reduced, and the elimination of the yield platform is facilitated.

According to the manufacturing method of the hot-dip galvanized low-alloy high-strength steel without the yield plateau, the hot rolling coiling temperature has influence on ferrite grain size and carbide precipitation, and in order to obtain fine ferrite structure and fine cementite precipitation, the coiling temperature is set to be 590 ℃ so as to promote pearlite transformation, reduce the solid solution C content of a finished product and be beneficial to eliminating the yield plateau. Meanwhile, the mechanical property uniformity of the whole steel strip in the length direction can be ensured by a U-shaped coiling mode with the coiling temperature 30 ℃ higher than that of the head and the tail of the hot rolling.

According to the manufacturing method of the hot-dip galvanized low-alloy high-strength steel without the yield platform, the shallow-groove turbulent-flow hydrochloric acid pickling and the five-stand tandem CVC + six-roller cold continuous rolling mill are adopted, so that the method has strong rolling capacity and can realize the production of 58-78% of large-range reduction rate.

The invention provides a method for manufacturing hot-dip galvanized low-alloy high-strength steel without a yield platform, which adopts a vertical full radiant tube heating continuous annealing furnace and a molten channel type induction heating ceramic zinc pot, wherein the annealing soaking temperature is 780 +/-3 ℃, and the steel strip is ensured to be completely recovered and recrystallized in the annealing process so as to obtain an equiaxial grain structure.

The manufacturing method of the hot-dip galvanized low-alloy high-strength steel without the yield platform adopts a four-roller wet-type finisher and a six-fold type two-bending one-straightening withdrawal and straightening machine, the elongation of the finisher is set to be 1.2-1.7%, the roller diameter of a working roller is phi 630-650 mm, the roughness of the working roller is 2.0-2.5 mu m, the speed of the finisher is 80-130mpm, and the elongation of the withdrawal and straightening machine is 0.2%, so that the control of a large finishing rolling force can be realized, and the yield platform of a steel strip can be eliminated.

The invention has the following beneficial effects: the hot-dip galvanized low-alloy high-strength steel HX340LAD + Z without the yield platform for the automobile sheet can ensure that dislocation gets rid of the action of solute atoms (Cochler gas clusters) of 'nail anchors' by reasonable component design and control of key process parameters such as hot rolling coiling temperature, finishing elongation and the like, can completely eliminate the yield platform, avoids the defect of slip lines (orange peel) generated in the reprocessing and forming process, improves the final surface quality of products, has excellent mechanical property, has the yield strength of more than or equal to 350MPa, the tensile strength of more than or equal to 450MPa and the elongation A80 of more than or equal to 25 percent, and meets the requirements of high-strength and high-surface in industries such as automobiles and the like.

Drawings

FIG. 1 is a drawing graph of a hot-dip galvanized low-alloy high-strength steel HX340LAD + Z without yield plateau for an automotive sheet in example 1 of the present invention.

Detailed Description

The following are specific examples of the present invention and further describe the technical solutions of the present invention, but the scope of the present invention is not limited to these examples. All changes, modifications and equivalents that do not depart from the spirit of the invention are intended to be included within the scope thereof.

The hot-dip galvanized low-alloy high-strength steel without yield platform for the automobile plate comprises the following chemical components in percentage by mass: c: 0.060 to 0.090%, Si is not more than 0.05%, Mn: 0.65-0.75%, P: 0.015-0.025%, S is less than or equal to 0.010%, Als: 0.025 to 0.06%, Nb: 0.025-0.035%, N is less than or equal to 0.0040%, and the balance is Fe and inevitable impurities.

The production process of hot galvanized low alloy high strength steel without yield platform for automobile sheet includes smelting, continuous casting, hot rolling, acid continuous rolling and hot galvanizing. In the hot rolling procedure, the outlet temperature of the hot rolling finish rolling is 890 +/-15 ℃, the cooling mode adopts front-stage laminar cooling, the coiling temperature is 590 +/-15 ℃, and the head and tail of the U-shaped coiling mode are 30 ℃ higher than the tail of the U-shaped coiling mode. The total reduction rate of the acid continuous rolling is 58-78%. The annealing soaking temperature of hot galvanizing is 780 +/-10 ℃, the elongation of a finishing machine is 1.2-1.7%, the finishing rolling force is 3000-8000 KN, the roll diameter of a working roll of the finishing machine is phi 630-650 mm, the roughness of the working roll of the finishing machine is 2.0-2.5 mu m, the speed of the finishing machine is 80-130mpm, and the elongation of a withdrawal and straightening machine is 0.2%.

The thickness specification of the steel is 0.5-2.5 mm, the width specification is 900-1850 mm, the yield strength is not less than 350MPa, the tensile strength is not less than 450MPa, the elongation A80 is not less than 25%, and a tensile curve has no yield platform.