阅读说明：本技术 一种一钢多级多厚度热轧双相钢及生产方法 (One-steel multi-stage multi-thickness hot-rolled dual-phase steel and production method thereof ) 是由 张志强 吕德文 贾改风 柳风林 李爱民 李娜 周建川 于 2019-10-24 设计创作，主要内容包括：本发明涉及一种一钢多级多厚度热轧双相钢,其化学成分重量百分含量为：C：0.06%-0.09%,Si：≤0.05%,Mn：1.1%-1.4%,Cr：0.45-0.65%,P：≤0.015%,S：≤0.005%,Als：0.015%-0.045%,余量为Fe及不可避免的杂质。生产方法中,铸坯加热工序,出加热炉温度为1250±20℃,加热时间≥180min；铸坯加热采用尾部温度补偿,尾部较头部温度高出20-40℃。本发明通过合理的成分设计和调整各工序段的关键工艺参数,实现采用一种成分可生产540MPa和590MPa两种不同强度级别,厚度从3mm到12mm的热轧双相钢；满足多客户、多用途、多厚度、多性能的个性化需求。(The invention relates to one-steel multi-stage multi-thickness hot-rolled dual-phase steel, which comprises the following chemical components in percentage by weight: c: 0.06% -0.09%, Si: less than or equal to 0.05 percent, Mn: 1.1% -1.4%, Cr: 0.45-0.65%, P: less than or equal to 0.015 percent, S: less than or equal to 0.005 percent, Als: 0.015% -0.045%, and the balance of Fe and inevitable impurities. In the production method, in the casting blank heating process, the temperature of a heating furnace is 1250 +/-20 ℃, and the heating time is more than or equal to 180 min; the casting blank is heated by adopting tail temperature compensation, and the temperature of the tail part is 20-40 ℃ higher than that of the head part. The invention realizes that the hot-rolled dual-phase steel with two different strength levels of 540MPa and 590MPa and the thickness of 3mm to 12mm can be produced by adopting one component through reasonable component design and adjustment of key process parameters of each process section; the individual requirements of multiple customers, multiple purposes, multiple thicknesses and multiple performances are met.)

1. A one-steel multi-stage multi-thickness hot-rolled dual-phase steel is characterized in that: the weight percentage of the chemical components is as follows: c: 0.06-0.09%, Si is less than or equal to 0.05%, Mn: 1.1% -1.4%, Cr: 0.45-0.65%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, Als: 0.015% -0.045%, and the balance of Fe and inevitable impurities.

2. A production method of one-steel multi-stage multi-thickness hot-rolled dual-phase steel comprises a steel-making-continuous casting process, a casting blank heating process, a casting blank rolling process, a strip steel cooling and coiling process; the method is characterized in that:

the thickness of a casting blank produced in the steelmaking-continuous casting process is 230-240mm, and the components in percentage by weight are as follows: c: 0.06-0.09%, Si is less than or equal to 0.05%, Mn: 1.1% -1.4%, Cr: 0.45-0.65%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, Als: 0.015% -0.045%, and the balance of Fe and inevitable impurities;

in the casting blank heating procedure, the temperature of the heating furnace is 1250 +/-20 ℃, and the heating time is more than or equal to 180 min; the casting blank is heated by adopting tail temperature compensation, and the temperature of the tail part is 20-40 ℃ higher than that of the head part.

3. A method for producing a one-steel multi-stage multi-thickness hot-rolled dual-phase steel as claimed in claim 2, wherein: in the casting blank rolling process, the rough rolling descaling pressure is ensured to be more than or equal to 190bar, the rough rolling start rolling temperature is 1100-1180 ℃, and the finish rolling start rolling temperature is more than or equal to 1030 ℃; the finishing temperature is 800-850 ℃.

4. A method for producing a one-steel multi-stage multi-thickness hot-rolled dual-phase steel as claimed in claim 2, wherein: the strip steel cooling and coiling process adopts a three-section cooling mode, namely front section concentrated cooling, air cooling and rear section cooling; the front section adopts concentrated cooling, the cooling speed is 45-100 ℃/s, the cooling is carried out to 650-700 ℃, then air cooling is carried out, the air cooling time is 3-13s, then the rear section is carried out conventional cooling, the cooling speed is 25-60 ℃/s, and the coiling temperature is 50-450 ℃; obtaining 540MPa hot-rolled dual-phase steel and 590MPa hot-rolled dual-phase steel with different strength grades.

5. The production method of one-steel multi-grade multi-thickness hot-rolled dual-phase steel as claimed in claim 4, wherein: when the final rolling temperature is 800-; the tensile curve has no yield platform, and the structure is ferrite + martensite + a small amount of granular bainite or ferrite + bainite.

6. The production method of one-steel multi-grade multi-thickness hot-rolled dual-phase steel as claimed in claim 4, wherein: when the final rolling temperature is 850 ℃ plus, the front section cooling speed is 45-100 ℃/s, the cooling is carried out to 650 ℃ plus 700 ℃, the air cooling time is 3-6s, the rear section cooling speed is 25-60 ℃/s, the coiling temperature is 50-250 ℃, DP590 Mpa-grade hot-rolled dual-phase steel with the thickness of 3-12mm is obtained, the yield strength is 359-415Mpa, the tensile strength is 612-653 Mpa, the elongation is 26-32%, the tensile curve has no yield platform, and the structure is ferrite + martensite.

Technical Field

The invention relates to dual-phase steel and a production method thereof, in particular to one-steel multi-stage multi-thickness hot-rolled dual-phase steel and a production method thereof.

Background

In recent years, with the development of energy conservation, weight reduction and safety of automobiles, hot-rolled dual-phase steel has the advantages of good strong plasticity, low yield ratio, high initial work hardening rate, good bake hardening performance, good fatigue resistance and the like, is widely used for manufacturing components such as automobile wheels, chassis, bumpers, various frames of automobile bodies and the like, can reduce the weight of the automobiles by 20-30%, meets the development theme of light weight, high performance, safety, environmental protection and energy conservation of automobile materials, and gradually becomes one of the preferred steel types of the automobile steel.

The hot-rolled dual-phase steel has wide application, more customers, large ordered thickness specification span and different ordered goods amount from 30 tons to 200 tons, and each large steel plant smelts about 7 to 10 furnaces for one casting time, and the steel in each furnace is more than 200 tons; if 1-2 furnaces of hot rolling dual-phase steel are smelted in one casting time, 4 mixed casting blanks are generated, so that the problems of difficult production structure, high cost of steel per ton and the like can be caused. Aiming at the characteristics of small ordering batch, multiple thickness specifications, high production organization difficulty and the like of the hot-rolled dual-phase steel, the dual-phase steel with different grades and different thicknesses can be produced by one composition system through reasonable composition system design and process parameter control of each process, so that the production organization can be optimized, the cost of steel per ton can be reduced, the contract conversion rate can be improved, and the individual requirements of multiple customers, multiple purposes, multiple thicknesses and multiple performances can be met.

The patent with the application number of CN201310621228 discloses a one-steel multi-stage hot rolled steel plate and a manufacturing method thereof, wherein the components contain 0.15-0.35% of Si element, red iron scales are easily formed on the surface of the steel plate, and the appearance quality is affected, and in addition, the thickness specification of the steel produced by the patent is 4-6mm, so that the requirements of more specifications of more customers cannot be effectively met.

Disclosure of Invention

The invention aims to provide one-steel multi-level multi-thickness hot-rolled dual-phase steel and a production method thereof, which can realize that one component can produce the hot-rolled dual-phase steel with two different strength levels of 540MPa and 590MPa and the thickness of 3-12mm by reasonably designing the components and adjusting key process parameters of each process section, the surface quality of a steel plate is good, and the individual requirements of multiple customers, multiple purposes, multiple thicknesses and multiple performances are met.

In order to solve the problems, the technical scheme adopted by the invention is as follows:

a one-steel multi-stage multi-thickness hot-rolled dual-phase steel comprises the following chemical components in percentage by weight: c: 0.06-0.09%, Si is less than or equal to 0.05%, Mn: 1.1% -1.4%, Cr: 0.45-0.65%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, Als: 0.015% -0.045%, and the balance of Fe and inevitable impurities.

A production method of one-steel multi-stage multi-thickness hot-rolled dual-phase steel comprises a steel-making-continuous casting process, a casting blank heating process, a casting blank rolling process, a strip steel cooling and coiling process;

the thickness of a casting blank produced in the steelmaking-continuous casting process is 230-240mm, and the components in percentage by weight are as follows: c: 0.06-0.09%, Si is less than or equal to 0.05%, Mn: 1.1% -1.4%, Cr: 0.45-0.65%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, Als: 0.015% -0.045%, and the balance of Fe and inevitable impurities;

in the casting blank heating procedure, the temperature of the heating furnace is 1250 +/-20 ℃, and the heating time is more than or equal to 180 min; the casting blank is heated by adopting tail temperature compensation, and the temperature of the tail part is 20-40 ℃ higher than that of the head part.

In the casting blank rolling process, the rough rolling descaling pressure is ensured to be more than or equal to 190bar, the rough rolling start rolling temperature is 1100-1180 ℃, and the finish rolling start rolling temperature is more than or equal to 1030 ℃; the finishing temperature is 800-850 ℃.

In the production method of the one-steel multi-stage multi-thickness hot-rolled dual-phase steel, the strip steel cooling and coiling process adopts a three-section cooling mode, namely front section concentrated cooling, air cooling and rear section cooling; different cooling speeds, intercooling temperatures and air cooling times have important influences on the size of ferrite grains and the form, distribution and content of martensite, and directly influence the mechanical property and the process property of the dual-phase steel; the front section adopts concentrated cooling, the cooling speed is 45-100 ℃/s, the cooling is carried out to 650-700 ℃, then air cooling is carried out, the air cooling time is 3-13s, then the rear section is carried out conventional cooling, the cooling speed is 25-60 ℃/s, and the coiling temperature is 50-450 ℃; obtaining 540MPa hot-rolled dual-phase steel and 590MPa hot-rolled dual-phase steel with different strength grades.

The production method of the one-steel multi-stage multi-thickness hot-rolled dual-phase steel comprises the steps of obtaining DP540 Mpa-grade hot-rolled dual-phase steel with the thickness of 3-12mm when the final rolling temperature is 800-; the tensile curve has no yield platform, and the structure is ferrite + martensite + a small amount of granular bainite or ferrite + bainite.

When the final rolling temperature is 800-.

The component system and the process parameter selection and analysis of the invention are as follows:

carbon: the carbon has extremely obvious strengthening effect and is the most economic strengthening element, but the carbon is very harmful to the toughness and the welding performance of steel; therefore, in order to obtain good welding performance of the hot-rolled dual-phase steel, the carbon content in the steel is reduced, but the content is not easy to be too low, and the C content ranges from 0.06% to 0.09%.

Silicon: silicon, as a carbon-excluding element, mainly plays roles of ferrite purification, austenite stability increase, and solid solution strengthening in dual-phase steel, but the presence of Si readily forms siliquote Fe₂SiO₄The steel is pinned on a steel matrix, so that the red iron scale defect appears on the surface of the steel coil, and Si is selected to be less than or equal to 0.05 percent.

Manganese: manganese is a main solid solution strengthening element, can expand an austenite region, has a strong austenite stabilizing effect, and reduces the temperature of Ar3 and Ar1, but when the content of Mn is too high, the steel plate has a serious banded structure, the anisotropy is enhanced, and the toughness is reduced, so that the content of Mn is controlled to be 1.1-1.4%.

Chromium: chromium is a medium-strength carbide forming element, the hardenability of the steel is obviously improved, the pearlite transformation and the bainite transformation can be strongly delayed, the coiling window is enlarged, in addition, the diffusion of C to austenite can be promoted by Cr, the yield strength of ferrite can be reduced, the low-yield-strength dual-phase steel can be obtained, and the Cr content ranges from 0.45% to 0.65%.

In the process of heating the casting blank, because the rolling speed of the hot-rolled dual-phase steel is low and the temperature drop is large in the rolling process, the heating temperature is not too low, the furnace temperature is determined to be 1250 +/-20 ℃, and the heating time is more than or equal to 180 min; in order to avoid the power jump caused by the increase of the load of the rolling mill due to the large temperature drop of the tail part, the tail part compensation is adopted for heating the casting blank, and the temperature is 20-40 ℃ higher than that of the head part.

In the casting blank rolling process, the rough rolling descaling pressure is ensured to be more than or equal to 190bar, the rough rolling initial rolling temperature is 1100-1180 ℃, and the finish rolling initial rolling temperature is more than or equal to 1030 ℃; the selection of the finish rolling temperature not only creates conditions for subsequent phase change, but also increases the accumulated deformation of a non-recrystallization region, refines austenite grains and further refines ferrite grains, and the finish rolling temperature is determined to be 800-850 ℃.

The invention has the beneficial effects that:

(1) in the production of a conventional hot continuous rolling production line, the hot-rolled dual-phase steel with the thickness of 3mm to 12mm can be produced by adopting one component through reasonable component design, adjustment of key process parameters of each process section and a slab tail temperature compensation mechanism, wherein the hot-rolled dual-phase steel can meet the requirement of producing two different strength levels of 540MPa and 590 MPa;

(2) because the content of Si element is more than 0.15 percent, the risk of red iron scale defects on the surface of the steel plate is greatly increased, the appearance quality of the steel plate after pickling is influenced, the Si element is not added (namely the Si is less than or equal to 0.05 percent), the defects are not generated in the production process, and the surface of the steel plate has no red embroidery quality defects.

(3) The production of the one-steel multi-level multi-thickness hot-rolled dual-phase steel not only solves the problems of small order batch, multiple thickness specifications and large production organization difficulty of the hot-rolled dual-phase steel, but also can reduce the cost of steel per ton, improve the contract exchange rate and meet the individual requirements of multiple customers, multiple purposes, multiple thicknesses and multiple performances by increasing the number of casting times.

Drawings

FIG. 1 shows the metallographic structure of a DP540 strip according to example 1 of the present invention;

FIG. 2 shows the metallographic structure of a DP590 steel strip according to example 1 of the present invention;

FIG. 3 shows the metallographic structure of a DP540 strip according to example 2 of the present invention;

FIG. 4 shows the metallographic structure of a DP590 steel strip according to example 2 of the present invention;

FIG. 5 shows the metallographic structure of a DP540 strip according to example 3 of the present invention;

FIG. 6 shows the metallographic structure of a DP590 steel strip according to example 3 of the present invention;

FIG. 7 shows the metallographic structure of a DP540 strip according to example 4 of the present invention;

FIG. 8 shows the metallographic structure of a DP590 steel strip according to example 4 of the present invention;

FIG. 9 shows the metallographic structure of a DP540 strip according to example 5 of the present invention;

FIG. 10 shows the metallographic structure of a DP590 steel strip according to example 5 of the present invention;

FIG. 11 shows the metallographic structure of a DP540 strip according to example 6 of the present invention;

FIG. 12 shows the metallographic structure of a DP590 steel strip according to example 6 of the present invention.

Detailed Description

A one-steel multi-stage multi-thickness hot-rolled dual-phase steel comprises the following chemical components in percentage by weight: c: 0.06-0.09%, Si is less than or equal to 0.05%, Mn: 1.1% -1.4%, Cr: 0.45-0.65%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, Als: 0.015% -0.045%, and the balance of Fe and inevitable impurities.

A production method of one-steel multi-stage multi-thickness hot-rolled dual-phase steel comprises the following specific steps:

(1) the steel making-continuous casting step comprises the following working procedures: blast furnace molten iron, top and bottom combined blown converter, LF refining, RH refining and continuous casting: pure molten steel is obtained through smelting, the continuous casting is controlled by adopting a constant drawing speed, and the thickness of a casting blank is 230-240 mm; the chemical components are as follows according to mass percent: c: 0.06-0.09%, Si is less than or equal to 0.05%, Mn: 1.1% -1.4%, Cr: 0.45-0.65%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, Als: 0.015% -0.045%, and the balance of Fe and inevitable impurities;

(2) and a casting blank heating procedure: the discharging temperature of the plate blank is 1250 +/-20 ℃, the heating time is more than or equal to 180min, and the tail part of the casting blank is 20-40 ℃ higher than the head part by adopting a tail part temperature compensation measure;

(3) and a casting blank rolling procedure: the descaling pressure of rough rolling is guaranteed to be more than or equal to 190bar, the initial rolling temperature of rough rolling is guaranteed to be 1100-1180 ℃, 3+5 passes of rolling are adopted, and in order to guarantee the surface quality, the descaling is carried out in all passes; cutting the head and the tail of the flying shear to ensure the head and the tail quality of the steel coil, wherein the finish rolling initial rolling temperature is more than or equal to 1030 ℃; the finishing mill F1-F4 adopts a high-speed steel roller, and the roller gap is lubricated to ensure that the steel plate has no scale pressing defect, and the finishing temperature is 800-;

(4) strip steel cooling and coiling: a three-section type cooling mode is adopted, namely front section concentrated cooling, air cooling and rear section cooling; cooling the steel to 650-700 ℃ at the cooling speed of 45-100 ℃/s at the front section, then carrying out air cooling for 3-13s, then entering the rear section for conventional cooling at the cooling speed of 25-60 ℃/s and the coiling temperature of 50-450 ℃, and obtaining the hot-rolled dual-phase steel with two different strength grades of 540MPa and 590MPa and the thickness specification of 3-12 mm.

Wherein when the final rolling temperature is 800-; the tensile curve has no yield platform, and the structure is ferrite + martensite + a small amount of granular bainite or ferrite + bainite.

When the final rolling temperature is 800-850 ℃, the front-section cooling speed is 45-100 ℃/s, the cooling is carried out to 650-700 ℃, the air cooling time is 3-6s, the rear-section cooling speed is 25-60 ℃/s, and the coiling temperature is 50-250 ℃, DP590 Mpa-grade hot-rolled dual-phase steel with the thickness of 3-12mm is obtained, the yield strength is 359-415Mpa, the tensile strength is 612-653 Mpa, the elongation is 26-32%, the tensile curve has no yield platform, and the structure is ferrite + martensite.

More specific examples of on-site production processes are as follows:

example 1

The process of the steel-making-continuous casting step comprises the following steps: blast furnace molten iron, top and bottom combined blown converter, LF refining, RH refining and continuous casting: pure molten steel is obtained through smelting, the continuous casting is controlled by adopting a constant drawing speed, and the thickness of a casting blank is 230 mm; the chemical components are as follows according to mass percent: c: 0.06%, Si: 0.03%, Mn: 1.2%, Cr: 0.45%, P: 0.012%, S: 0.004%, Als: 0.015% and the balance of Fe and inevitable impurities;

respectively producing 540 MPa-grade and 590 MPa-grade hot-rolled dual-phase steel with the thickness of 3mm by adopting the continuous casting billets;

(1) the 540 Mpa-grade hot-rolled dual-phase steel with the thickness of 3mm is produced, and the process comprises the following steps:

a casting blank heating procedure: the discharging temperature of the plate blank is 1270 ℃, and the heating time is 180 min; the temperature of the tail part is 40 ℃ higher than that of the head part.

Casting blank rolling procedure: the rough rolling descaling pressure is 190bar, the rough rolling starting temperature is 1180 ℃, 3+5 passes of rolling are adopted, and the thickness of the intermediate blank is 38 mm; the finish rolling initial rolling temperature is 1071 ℃; the finishing temperature is 800 ℃;

strip steel cooling and coiling: a three-section cooling mode is adopted, the front section cooling speed is 100 ℃/s, the cooling is carried out to 700 ℃, then the air cooling is carried out, the air cooling time is 7s, and then the cooling enters the rear section for cooling, and the cooling speed is 60 ℃/s; the coiling temperature is 450 ℃;

the DP540Mpa hot-rolled dual-phase steel with the thickness of 3mm is obtained, the yield strength is 363Mpa, the tensile strength is 576 Mpa, and the elongation is 28%. The tensile curve has no yield plateau; the structure is ferrite, martensite and a small amount of granular bainite, and the yield ratio is 0.64.

(2) The 590 Mpa-grade hot-rolled dual-phase steel with the thickness of 3mm is produced by the following technical process:

a casting blank heating procedure: the discharging temperature of the plate blank is 1270 ℃, the heating time is 180min, and the temperature of the tail part is 40 ℃ higher than that of the head part;

casting blank rolling procedure: the rough rolling descaling pressure is ensured to be 190bar, the rough rolling starting temperature is 1180 ℃, 3+5 passes of rolling are adopted, and the thickness of the intermediate blank is 37 mm; the initial rolling temperature of finish rolling is 1063 ℃; the finishing temperature is 800 ℃;

strip steel cooling and coiling: a three-section cooling mode is adopted, the front section cooling speed is 100 ℃/s, the cooling is carried out to 700 ℃, then the air cooling is carried out, the air cooling time is 3s, and then the cooling enters the rear section for cooling, and the cooling speed is 60 ℃/s; the coiling temperature is 250 ℃;

obtaining DP590Mpa hot-rolled dual-phase steel with the thickness of 3mm, wherein the yield strength is 415Mpa, the tensile strength is 653 Mpa, the elongation is 29 percent, and the yield ratio is 0.63; the tensile curve has no yield plateau; the structure is ferrite + martensite, and the martensite content is 14%.

Example 2

The process of the steel-making and continuous casting step comprises the following steps: blast furnace molten iron, top and bottom combined blown converter, LF refining, RH refining and continuous casting: pure molten steel is obtained through smelting, the continuous casting is controlled by adopting a constant drawing speed, and the thickness of a casting blank is 235 mm; the chemical components are as follows according to mass percent: c: 0.07%, Si: 0.05%, Mn: 1.1%, Cr: 0.48%, P: 0.015%, S: 0.005%, Als: 0.032%, and the balance of Fe and inevitable impurities;

respectively producing 540 Mpa-grade and 590 Mpa-grade hot-rolled dual-phase steel with the thickness of 5mm by adopting the casting blank;

(1) and 540 Mpa-grade hot-rolled dual-phase steel with the thickness of 5mm is produced, and the process comprises the following steps:

a casting blank heating procedure: the discharging temperature of the plate blank is 1265 ℃, and the heating time is 195 min; the temperature of the tail part is 38 ℃ higher than that of the head part;

casting blank rolling procedure: the rough rolling descaling pressure is 201bar, the rough rolling starting temperature is 1175 ℃, 3+5 passes of rolling are adopted, and the thickness of the intermediate blank is 38 mm; the initial rolling temperature of finish rolling is 1070 ℃; the finishing temperature is 813 ℃;

strip steel cooling and coiling: adopting a three-section cooling mode, wherein the front section cooling speed is 96 ℃/s, cooling to 693 ℃, then carrying out air cooling for 7.5s, and then entering the rear section for cooling, wherein the cooling speed is 54 ℃/s; the coiling temperature is 433 ℃;

the hot rolled dual phase steel with the thickness of 5mm and the DP540Mpa grade is obtained, and the yield strength is 405Mpa, the tensile strength is 589 Mpa, and the elongation is 31.5 percent. The tensile curve has no yield plateau; the structure is ferrite and bainite, and the yield ratio is 0.69.

(2) The 590Mpa hot-rolled dual-phase steel with the thickness of 5mm is produced by the following technical processes:

a casting blank heating procedure: the discharging temperature of the plate blank is 1263 ℃, the heating time is 195min, and the tail temperature is 39 ℃ higher than the head temperature.

Casting blank rolling procedure: the rough rolling descaling pressure is guaranteed to be 195bar, the rough rolling starting temperature is 1169 ℃, 3+5 passes of rolling are adopted, and the thickness of the intermediate blank is 38 mm; the initial rolling temperature of finish rolling is 1068 ℃; the finishing temperature is 809 ℃;

strip steel cooling and coiling: a three-section cooling mode is adopted, the cooling speed of the front section is 93 ℃/s, the cooling is carried out to 693 ℃, then air cooling is carried out, the air cooling time is 3.5s, and then the cooling enters the second stage for cooling, and the cooling speed is 52 ℃/s; the coiling temperature is 231 ℃;

the hot-rolled dual-phase steel with the thickness of 5mm and the DP590Mpa grade is obtained, and has the yield strength of 387Mpa, the tensile strength of 643 Mpa, the elongation of 27 percent and the yield ratio of 0.60. The tensile curve has no yield plateau; the structure is ferrite + martensite, and the martensite content is 11.3%.

Example 3

The process of the steel-making and continuous casting step comprises the following steps: blast furnace molten iron, top and bottom combined blown converter, LF refining, RH refining and continuous casting: pure molten steel is obtained through smelting, the continuous casting is controlled by adopting a constant drawing speed, and the thickness of a casting blank is 236 mm; the chemical components are as follows according to mass percent: c: 0.07%, Si: 0.03%, Mn: 1.25%, Cr: 0.52%, P: 0.014%, S: 0.004%, Als: 0.043%, the balance being Fe and inevitable impurities;

respectively producing 540 Mpa-grade and 590 Mpa-grade hot-rolled dual-phase steel with the thickness of 7mm by adopting the casting blank;

(1) and producing 540 Mpa-grade hot-rolled dual-phase steel with the thickness of 7mm, wherein the process comprises the following steps:

a casting blank heating procedure: the tapping temperature of the plate blank is 1252 ℃, the heating time is 215min, and the temperature of the tail part is 32 ℃ higher than that of the head part;

casting blank rolling procedure: the rough rolling descaling pressure is 205bar, the rough rolling starting temperature is 1162 ℃, 3+5 passes of rolling are adopted, and the thickness of the intermediate blank is 42 mm; the initial rolling temperature of finish rolling is 1064 ℃; the finishing temperature is 817 ℃;

strip steel cooling and coiling: adopting a three-section cooling mode, wherein the front section cooling speed is 83 ℃/s, cooling to 683 ℃, then carrying out air cooling for 9s, and then entering the rear section for cooling, wherein the cooling speed is 56 ℃/s; the coiling temperature is 425 ℃;

obtaining DP540Mpa grade hot rolling dual-phase steel with the thickness of 7mm, the yield strength of 396Mpa, the tensile strength of 562 Mpa, the elongation of 35 percent and no yield platform of a tensile curve; the structure is ferrite and bainite, and the yield ratio is 0.70.

(2) And producing 590 Mpa-grade hot-rolled dual-phase steel with the thickness of 7mm, wherein the technical process comprises the following steps of:

a casting blank heating procedure: the tapping temperature of the plate blank is 1253 ℃, the heating time is 207min, and the tail temperature is 35 ℃ higher than the head temperature;

casting blank rolling procedure: the rough rolling descaling pressure is ensured to be 205bar, the rough rolling starting temperature is 1159 ℃, 3+5 passes of rolling are adopted, and the thickness of the intermediate blank is 42 mm; the finish rolling start temperature is 1057 ℃; the finishing temperature is 823 ℃;

strip steel cooling and coiling: adopting a three-section cooling mode, wherein the front section cooling speed is 85 ℃/s, cooling to 678 ℃, then carrying out air cooling for 4s, and then entering the rear section for cooling, wherein the cooling speed is 45 ℃/s; the coiling temperature was 231 ℃.

Obtaining DP590Mpa hot-rolled dual-phase steel with the thickness of 7mm, wherein the yield strength is 359Mpa, the tensile strength is 632 Mpa, the elongation is 26 percent, and the yield ratio is 0.57; the tensile curve has no yield plateau; the structure is ferrite + martensite, and the martensite content is 14%.

Example 4

The process of the steel-making and continuous casting step comprises the following steps: blast furnace molten iron, top and bottom combined blown converter, LF refining, RH refining and continuous casting: pure molten steel is obtained through smelting, the continuous casting is controlled by adopting a constant drawing speed, and the thickness of a casting blank is 236 mm; the chemical components are as follows according to mass percent: c: 0.07%, Si: 0.03%, Mn: 1.25%, Cr: 0.52%, P: 0.014%, S: 0.004%, Als: 0.043%, the balance being Fe and inevitable impurities;

respectively producing 540 Mpa-grade and 590 Mpa-grade hot-rolled dual-phase steel with the thickness of 8.5mm by adopting the casting blank;

(1) and 540 Mpa-grade hot-rolled dual-phase steel with the thickness of 8.5mm is produced, and the process comprises the following steps:

a casting blank heating procedure: the discharging temperature of the plate blank is 1250 ℃, the heating time is 207min, and the tail temperature is 30 ℃ higher than the head temperature;

casting blank rolling procedure: the rough rolling descaling pressure is 203bar, the rough rolling starting temperature is 1141 ℃, 3+5 passes of rolling are adopted, and the thickness of the intermediate blank is 44 mm; the finish rolling initial rolling temperature is 1054 ℃; the finishing temperature is 827 ℃;

strip steel cooling and coiling: adopting a three-section cooling mode, wherein the front section cooling speed is 65 ℃/s, cooling to 665 ℃, then carrying out air cooling for 10s, and then entering the rear section cooling, wherein the cooling speed is 45 ℃/s; the coiling temperature is 382 ℃;

obtaining DP540Mpa hot-rolled dual-phase steel with the thickness of 8.5mm, the yield strength of 401Mpa, the tensile strength of 560 Mpa, the elongation of 30.5 percent and no yield platform of a tensile curve; the structure is ferrite and bainite, and the yield ratio is 0.72.

(2) And producing 590 Mpa-grade hot-rolled dual-phase steel with the thickness of 8.5mm, wherein the process comprises the following steps:

a casting blank heating procedure: the tapping temperature of the plate blank is 1247 ℃, the heating time is 198min, and the temperature of the tail part is 30 ℃ higher than that of the head part;

casting blank rolling procedure: the rough rolling descaling pressure is ensured to be 200bar, the rough rolling starting temperature is 1145 ℃, 3+5 passes of rolling are adopted, and the thickness of the intermediate billet is 44 mm; the finish rolling start temperature is 1048 ℃; the finishing temperature is 826 ℃;

strip steel cooling and coiling: adopting a three-section cooling mode, wherein the front section cooling speed is 71 ℃/s, cooling to 671 ℃, then carrying out air cooling for 5s, and then entering the rear section for cooling, wherein the cooling speed is 41 ℃/s; the coiling temperature was 195 ℃.

Obtaining the DP590Mpa hot-rolled dual-phase steel with the thickness of 8.5mm, the yield strength of 362Mpa, the tensile strength of 619 Mpa, the elongation of 28 percent and the yield ratio of 0.58; the tensile curve has no yield platform, the structure is ferrite and martensite, and the martensite content is 15%.

Example 5

The process of the steel-making and continuous casting step comprises the following steps: blast furnace molten iron, top and bottom combined blown converter, LF refining, RH refining and continuous casting: pure molten steel is obtained through smelting, the continuous casting is controlled by adopting a constant drawing speed, and the thickness of a casting blank is 240 mm; the chemical components are as follows according to mass percent: c: 0.08%, Si: 0.05%, Mn: 1.3%, Cr: 0.6%, P: 0.013%, S: 0.003%, Als: 0.037%, the balance being Fe and unavoidable impurities;

respectively producing 540 Mpa-grade and 590 Mpa-grade hot-rolled dual-phase steel with the thickness of 10mm by adopting the casting blanks;

(1) and 540 Mpa-grade hot-rolled dual-phase steel with the thickness of 10mm is produced, and the production process comprises the following steps:

a casting blank heating procedure: the discharging temperature of the plate blank is 1235 ℃, the heating time is 201min, and the tail temperature is 25 ℃ higher than the head temperature;

casting blank rolling procedure: the rough rolling descaling pressure is 198bar, the rough rolling starting temperature is 1125 ℃, 3+5 passes of rolling are adopted, and the thickness of the intermediate blank is 45 mm; the starting temperature of finish rolling is 1042 ℃; the finishing temperature is 841 ℃;

strip steel cooling and coiling: adopting a three-section cooling mode, wherein the front section cooling speed is 53 ℃/s, cooling to 660 ℃, then carrying out air cooling for 11s, and then entering the rear section for cooling, wherein the cooling speed is 33 ℃/s; the coiling temperature was 302 ℃.

Obtaining DP540Mpa grade hot-rolled dual-phase steel with the thickness of 10mm, the yield strength of 382Mpa, the tensile strength of 565 Mpa and the elongation of 29 percent; the tensile curve has no yield plateau; the structure is ferrite and bainite, and the yield ratio is 0.68.

(2) And producing 590 Mpa-grade hot-rolled dual-phase steel with the thickness of 10mm, wherein the process comprises the following steps:

a casting blank heating procedure: the discharging temperature of the plate blank is 1234 ℃, the heating time is 201min, and the temperature of the tail part is 23 ℃ higher than that of the head part;

casting blank rolling procedure: the rough rolling descaling pressure is ensured to be 201bar, the rough rolling starting temperature is 1119 ℃, 3+5 passes of rolling are adopted, and the thickness of the intermediate billet is 45 mm; the starting temperature of finish rolling is 1040 ℃; the finishing temperature is 847 ℃;

strip steel cooling and coiling: adopting a three-section cooling mode, wherein the front section cooling speed is 57 ℃/s, cooling to 671 ℃, then carrying out air cooling for 5.5s, and then entering the rear section for cooling, wherein the cooling speed is 36 ℃/s; the coiling temperature was 114 ℃.

Obtaining DP590Mpa hot-rolled dual-phase steel with the thickness of 10mm, wherein the yield strength is 365Mpa, the tensile strength is 624Mpa, the elongation is 32 percent, and the yield ratio is 0.58; fig. 10 shows that the tensile curve has no yield plateau, the microstructure is ferrite + martensite, and the martensite content is 13.4%.

Example 6

The process of the steel-making and continuous casting step comprises the following steps: blast furnace molten iron, top and bottom combined blown converter, LF refining, RH refining and continuous casting: pure molten steel is obtained through smelting, the continuous casting is controlled by adopting a constant drawing speed, and the thickness of a casting blank is 240 mm; the chemical components are as follows according to mass percent: c: 0.09%, Si: 0.05%, Mn: 1.4%, Cr: 0.65%, P: 0.013%, S: 0.003%, Als: 0.045%, and the balance of Fe and inevitable impurities;

respectively producing 540 MPa-grade and 590 MPa-grade hot-rolled dual-phase steel with the thickness of 12mm by adopting the casting blanks;

(1) and 540 Mpa-grade hot-rolled dual-phase steel with the thickness of 12mm is produced, and the process flow comprises the following steps:

a casting blank heating procedure: the discharging temperature of the plate blank is 1230 ℃, and the heating time is 201 min; the temperature of the tail part is 20 ℃ higher than that of the head part;

casting blank rolling procedure: the rough rolling descaling pressure is 190bar, the rough rolling starting temperature is 1100 ℃, 3+5 passes of rolling are adopted, and the thickness of the intermediate blank is 46 mm; the finishing rolling initial temperature is 1030 ℃; the finishing temperature is 850 ℃;

strip steel cooling and coiling: adopting a three-section cooling mode, wherein the front section cooling speed is 45 ℃/s, cooling to 650 ℃, then carrying out air cooling for 13s, and then entering the rear section for cooling, wherein the cooling speed is 25 ℃/s; the coiling temperature is 200 ℃;

obtaining DP540Mpa grade hot rolling dual-phase steel with the thickness of 12mm, wherein the yield strength is 335Mpa, the tensile strength is 552 Mpa, the elongation is 35%, and the tensile curve has no yield platform; the structure is ferrite and bainite, and the yield ratio is 0.60.

(2) The 590 Mpa-grade hot-rolled dual-phase steel with the thickness of 12mm is produced, and the process flow comprises the following steps:

a casting blank heating procedure: the discharging temperature of the plate blank is 1230 ℃, the heating time is 201min, and the temperature of the tail part is 20 ℃ higher than that of the head part;

casting blank rolling procedure: the rough rolling descaling pressure is ensured to be 190bar, the rough rolling starting temperature is 1100 ℃, 3+5 passes of rolling are adopted, and the thickness of the intermediate blank is 46 mm; the finishing rolling initial temperature is 1030 ℃; the finishing temperature is 850 ℃;

strip steel cooling and coiling: adopting a three-section cooling mode, wherein the front section cooling speed is 45 ℃/s, cooling to 650 ℃, then carrying out air cooling for 6s, and then entering the rear section for cooling, wherein the cooling speed is 25 ℃/s; the coiling temperature was 50 ℃.

Obtaining DP590Mpa grade hot rolling dual-phase steel with the thickness of 12mm, wherein the yield strength is 368Mpa, the tensile strength is 612 Mpa, the elongation is 32 percent, the yield ratio is 0.60, and the tensile curve has no yield platform; the structure is ferrite + martensite, and the martensite content is 15.6%.