CN109929982A - Production method of high-strength steel - Google Patents

Abstract

The invention discloses a production method of high-strength steel. The composition of the steel grade is designed. Specifically: adding Si element for strengthening, after heating, an anchor-like pinning morphology appeared on the interface of adding, FeO wrapped Fe ₂ SiO ₄ and immersed into the steel matrix, the deepest pinning depth could reach 50 μm, and the inner iron sheet adhesion was relatively high. Well, it is not easy for the substrate to fall off. Cr and Mo were also added, and the morphology of the meshed iron sheet after reducing the Si content was weakened. Due to the addition of Mo element, there is a Mo element enriched band at the matrix interface. Mo element is less involved in the formation of internal oxide particles, and plays the role of sealing the oxidation interface. The removal power of the scale can be significantly improved by adding P element. The inclusion of P in the Fe-Si-O system can reduce the melting point of the oxides. Therefore, the addition of P element can significantly improve the removal force of the iron sheet, thereby reducing the adhesion of the iron sheet. The invention solves the technical problem of chromatic aberration defects, and can effectively reduce the occurrence rate of chromatic aberration defects of cold-rolled sheets, thereby improving product surface quality.

Description

A kind of production method of high strength steel

technical field

The invention relates to the technical field of steel rolling, in particular to a production method of high-strength steel.

Background technique

In the field of automobile manufacturing, automobile parts have a high demand for steel, including good strength, excellent formability, good corrosion resistance, weldability and coating performance. In addition to meeting safety requirements, high-strength steels also face higher and higher requirements for surface quality. High-strength steel is also gradually applied to parts in visible positions, such as doors, door sills, etc., using 400MPa-level high-strength steel; door inner panel using 590MPa-level high-strength steel; inner panel reinforcements Using 980MPa-1470MPa high-strength steel, etc. .

However, due to the addition of easily oxidizable alloying elements such as Si and Cr, DP and TRIP steels will have a series of color difference problems on the surface, such as increased adhesion of iron sheets, unclean residual pickling of red iron sheets, and then inherited to the cold-rolled finished products, manifested as The color difference of the strip after pickling then leads to the color difference defect of cold rolling. This directly limits the use of steel plates as visual components, which becomes a bottleneck and brings trouble to customers.

SUMMARY OF THE INVENTION

The present invention solves the technical problem of chromatic aberration defects in the prior art by providing a method for producing high-strength steel, and achieves the technical effect of effectively reducing the occurrence rate of chromatic aberration defects in cold-rolled sheets, thereby improving product surface quality.

The invention provides a method for producing high-strength steel, comprising:

Control the composition content of steel grades by mass percentage: control the Si content to be less than 0.3%, add Cr element at 0.2%-0.5%, add Mo element at 0.2%-0.5%, control P element at 0.01%-0.04% for steelmaking, get molten steel

Continuous casting is performed on the obtained molten steel to obtain a slab;

hot rolling the obtained slab;

The rolled slab is continuously withdrawn.

Further, the hot rolling of the obtained slab includes:

The obtained slab is heated, rough rolled, finish rolled and coiled.

Further, during the heating process, the furnace temperature is controlled at 1180°C-1200°C, the soaking time is controlled at 30min-35min, and the total time in the furnace is controlled at 150min-180min.

Further, in the process of finishing rolling, a double-pass descaling process is adopted.

Further, in the process of finishing rolling, the proportion of cooling water between the stands of the first three rolling mills is 50%, and the opening ratio of roll gap water reaches 80%.

Further, during the coiling process, the hot-rolled sheet is cooled by adopting a front-end intensive cooling mode or an ultra-fast cooling cooling mode.

Further, during the coiling process, the coiling temperature is controlled at 500°C-600°C.

Further, after the hot rolling of the obtained slab, it also includes:

The slab after hot rolling is pickled.

Further, after the hot-rolled slab is pickled, it also includes:

The slab after pickling is cold rolled.

Further, during the pickling process, the overall cold rolling reduction ratio is controlled within 70%.

One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

The composition of the steel grade is designed. Specifically: 0.3% Si element is added to the steel for strengthening. After heating at high temperature, an obvious anchor-like pinning morphology appears at the addition interface. FeO wraps Fe ₂ SiO ₄ and immerses into the steel matrix, and the pinning depth is the deepest. Up to 50μm, the inner iron sheet has good adhesion, and it is not easy for the substrate to fall off. In addition, 0.2%-0.5% of Cr and 0.2%-0.5% of Mo are added to the steel, and the morphology of the mesh iron sheet after reducing the Si content is significantly weakened, especially in the inner oxide layer close to the matrix. enriched, and the reticulated iron chains were obviously broken and weakened. At the same time, due to the addition of Mo element, there is an obvious Mo element enrichment band at the interface of the matrix, and the enrichment depth corresponds to the internal oxide particles. At the same time, Mo element is less involved in the formation of internal oxide particles, and mainly plays the role of sealing the oxidation interface. In addition, by adding the P element, the removal power of the iron sheet can be significantly improved. The content of P in Fe-Si-O system can reduce the melting point of the oxides, which is mainly due to the formation of a ternary eutectic system: FeO-Fe ₂ SiO ₄ -Fe ₃ (PO ₄ ) ₂ . Therefore, the addition of P element can significantly improve the removal force of the iron sheet, thereby reducing the adhesion of the iron sheet. In summary, the present invention solves the technical problem of chromatic aberration defects in the prior art, and achieves the technical effect of effectively reducing the occurrence rate of chromatic aberration defects in cold-rolled sheets, thereby improving product surface quality.

Description of drawings

Fig. 1 is the flow chart of the production method of high-strength steel provided by the embodiment of the present invention;

Fig. 2 is the surface morphology after cold rolling of the high-strength steel after adopting the production method of the high-strength steel provided by the embodiment of the present invention in Embodiment 1;

FIG. 3 shows the surface morphology of the high-strength steel after cold rolling in the second embodiment using the production method of the high-strength steel provided by the embodiment of the present invention.

Detailed ways

The embodiment of the present invention solves the technical problem of chromatic aberration defects in the prior art by providing a method for producing high-strength steel, and achieves the technical effect of effectively reducing the occurrence rate of chromatic aberration defects in cold-rolled sheets, thereby improving product surface quality.

The technical solution in the embodiment of the present invention is to solve the above problem, and the general idea is as follows:

The composition of the steel grade is designed. Specifically: 0.3% Si element is added to the steel for strengthening. After heating at high temperature, an obvious anchor-like pinning morphology appears at the addition interface. FeO wraps Fe ₂ SiO ₄ and immerses into the steel matrix, and the pinning depth is the deepest. Up to 50μm, the inner iron sheet has good adhesion, and it is not easy for the substrate to fall off. In addition, 0.2%-0.5% of Cr and 0.2%-0.5% of Mo are added to the steel, and the morphology of the mesh iron sheet after reducing the Si content is significantly weakened, especially in the inner oxide layer close to the matrix. enriched, and the reticulated iron chains were obviously broken and weakened. At the same time, due to the addition of Mo element, there is an obvious Mo element enrichment band at the matrix interface, and the enrichment depth corresponds to the internal oxide particles. At the same time, Mo element is less involved in the formation of internal oxide particles, and mainly plays the role of sealing the oxidation interface. In addition, by adding the P element, the removal power of the iron sheet can be significantly improved. The content of P in Fe-Si-O system can reduce the melting point of the oxides, which is mainly due to the formation of a ternary eutectic system: FeO-Fe ₂ SiO ₄ -Fe ₃ (PO ₄ ) ₂ . Therefore, the addition of P element can significantly improve the removal force of the iron sheet, thereby reducing the adhesion of the iron sheet. In summary, the embodiments of the present invention solve the technical problem of chromatic aberration defects in the prior art, and achieve the technical effect of effectively reducing the incidence of chromatic aberration defects in cold-rolled sheets, thereby improving product surface quality.

In order to better understand the above technical solutions, the above technical solutions will be described in detail below with reference to the accompanying drawings and specific embodiments.

Referring to Fig. 1, the production method of high-strength steel provided by the embodiment of the present invention includes:

Step S110: control the composition content of the steel grade by mass percentage: control the Si content to be less than 0.3%, add Cr element at 0.2%-0.5%, add Mo element at 0.2%-0.5%, and control P element at 0.01%-0.04% steel, get molten steel;

Step S120: performing continuous casting on the obtained molten steel to obtain a slab;

Step S130: hot rolling the obtained slab;

To specifically describe this step, step S130 includes:

The obtained slab is subjected to furnace heating, rough rolling, finish rolling and coiling.

In order to minimize the invasion of the iron sheet by the liquefaction of the fayalite phase formed by the high temperature of the Si element and the pinning depth of the anchor-like iron sheet structure, during the heating process, the furnace temperature was controlled at 1180℃-1200℃, and the soaking time was Controlled at 30min-35min, the total time in the furnace is controlled at 150min-180min.

In order to control the entry temperature of finishing rolling within the allowable range of rolling, a thermal insulation cover is used after rough rolling.

In order to ensure the descaling effect of finishing rolling, a double-pass descaling process is adopted in the process of finishing rolling. Increase the rolling speed to more than 8m/s.

In order to improve the quality of the roll surface of the lower mill, thereby improving the surface quality of the hot-rolled strip, in the process of finishing rolling, the proportion of cooling water between the first three mill stands is 50%, and the proportion of opening water between the roll gaps reaches 80%. At the same time, the rolling lubrication process is put into operation, and the final rolling temperature is controlled at 900℃-920℃.

In order to strengthen the structure strength of the surface layer of the hot-rolled sheet, reduce the hardness difference between the surface structure and the core, refine the grain size of the hot-rolled sheet, and improve the cold-rolled cracking inhibition ability of the surface layer of the steel sheet, in the process of coiling, the front end intensive cooling is adopted. mode or ultra-fast cooling mode to cool the hot-rolled sheet.

In order to further refine the microstructure and grain size of the hot-rolled sheet, inhibit the formation of subsurface stripes, and reduce the occurrence of surface cracking during cold rolling, the coiling temperature is controlled at 500℃-600℃ during the coiling process. °C.

Step S140: Continuously withdraw the rolled slab.

The production method of the high-strength steel provided by the embodiment of the present invention is specifically described. After hot rolling the obtained slab, the method further includes:

The slab after hot rolling is pickled.

The production method of the high-strength steel provided by the embodiment of the present invention is further described. After the hot-rolled slab is pickled, the method further includes:

The slab after pickling is cold rolled.

In order to avoid the occurrence of cracking along the grain boundary during the cold rolling process due to the difference in the phase boundary strength and the difference in the grain size of the hot-rolled structure between the surface layer and the core, the overall cold rolling reduction rate was controlled at 70 during the pickling process. % or less.

The production method of the high-strength steel provided by the embodiment of the present invention is further described. After the rolled slab is continuously withdrawn, the method further includes:

Flatten the slab after continuous retreat.

The production method provided by the embodiment of the present invention is specifically implemented on the Shougang Qian'an 2250 hot rolling production line and the Shougang Shunyi acid rolling production line, and the on-site surface quality is tracked.

Example 1:

The composition design of steel grades is shown in Table 1 below. The composition design only adopts the Si-Cr-Mo composition system. The Si element content is as high as 0.2%, the Cr element is controlled at 0.5%, and the Mo element is controlled at 0.2%. At the same time, an appropriate amount of P element is added to 0.03%. %, and the hot rolling process route formulated is shown in Table 2 below. The temperature of hot rolling is controlled at 1180℃, and the time in the furnace is controlled at 170min. Double-pass descaling is adopted for finishing rolling. The inlet temperature of finishing rolling is 1000℃. The proportion of cooling water between the three stands before finishing rolling is 50%. The roll gap water opening ratio reaches 80%. At the same time, the rolling lubrication process was put into operation, and the final rolling temperature was controlled at 910 °C. The coiling adopts the front-end intensive cooling mode, the coiling temperature is controlled at 580°C, and the cold rolling reduction rate is controlled at 70%. Tracking the surface after cold rolling, the surface quality is good and there is no color difference defect as shown in Figure 2.

Steel grade C Si Cr Mo P DP780 0.1 0.2 0.5 0.2 0.03

Table 1 Design of steel composition

Table 2 Hot rolling process route

Embodiment 2:

The composition design of steel grades is shown in Table 3 below. The composition design only adopts the Si-Cr-Mo composition system. The Si element content is as high as 0.2%, the Cr element is controlled at 0.2%, and the Mo element is controlled at 0.5%. At the same time, an appropriate amount of P element is added to 0.02%. %, the hot rolling process route formulated is shown in Table 4 below. The temperature of hot rolling is controlled at 1190℃, and the time in the furnace is controlled at 180min. Double-pass descaling is adopted for finishing rolling. The inlet temperature of finishing rolling is 990℃. The proportion of cooling water between the three stands before finishing rolling is 50%. The roll gap water opening ratio reaches 80%. At the same time, the rolling lubrication process was put into operation, and the finishing rolling temperature was controlled at 900℃. The coiling adopts the front-end ultra-fast cold cooling mode, the coiling temperature is controlled at 570°C, and the cold rolling reduction rate is controlled at 65%. Tracking the surface after cold rolling, the surface quality is good and there is no color difference defect as shown in Figure 3.

Steel grade C Si Cr Mo P DP780 0.15 0.2 0.2 0.5 0.02

Table 3 Steel composition design

Table 4 Hot rolling process route

【Technical effect】

1. The composition of steel grades is designed. Specifically: 0.3% Si element is added to the steel for strengthening. After heating at high temperature, an obvious anchor-like pinning morphology appears at the addition interface. FeO wraps Fe ₂ SiO ₄ and immerses into the steel matrix, and the pinning depth is the deepest. Up to 50μm, the inner iron sheet has good adhesion, and it is not easy for the substrate to fall off. In addition, 0.2%-0.5% of Cr and 0.2%-0.5% of Mo are added to the steel, and the morphology of the mesh iron sheet after reducing the Si content is significantly weakened, especially in the inner oxide layer close to the matrix. enriched, and the reticulated iron chains were obviously broken and weakened. At the same time, due to the addition of Mo element, there is an obvious Mo element enrichment band at the matrix interface, and the enrichment depth corresponds to the internal oxide particles. At the same time, Mo element is less involved in the formation of internal oxide particles, and mainly plays the role of sealing the oxidation interface. In addition, by adding the P element, the removal power of the iron sheet can be significantly improved. The content of P in Fe-Si-O system can reduce the melting point of the oxides, which is mainly due to the formation of a ternary eutectic system: FeO-Fe ₂ SiO ₄ -Fe ₃ (PO ₄ ) ₂ . Therefore, the addition of P element can significantly improve the removal force of the iron sheet, thereby reducing the adhesion of the iron sheet. In summary, the embodiments of the present invention solve the technical problem of chromatic aberration defects in the prior art, and achieve the technical effect of effectively reducing the incidence of chromatic aberration defects in cold-rolled sheets, thereby improving product surface quality.

2. During the heating process, the temperature of the furnace should be controlled at 1180℃-1200℃, the soaking time should be controlled at 30min-35min, and the total time in the furnace should be controlled at 150min-180min. By reducing the tapping temperature and shortening the time in the furnace, on the one hand, the generation of raw iron oxide scale in the furnace can be reduced; The state of iron sheet on the surface of the rolled sheet can inhibit the residual iron sheet, improve the flatness of the interface between the iron sheet and the substrate, avoid the generation of tingling defects after pickling, and thus inhibit the generation of color difference defects after cold rolling.

3. In the process of finishing rolling, the double-pass descaling process is adopted to ensure the descaling effect of finishing rolling.

4. In the process of finishing rolling, the ratio of cooling water between the first three rolling mill stands is 50%, and the ratio of opening water in the roll gap reaches 80%, which improves the quality of the roll surface of the lower mill, thereby improving the surface quality of the hot-rolled strip.

5. The use of thermal insulation cover after rough rolling avoids the risk of increased rolling force and stacking due to low strip temperature.

6. In the process of finishing rolling, the final rolling temperature is controlled at 900℃-920℃, which not only reduces the rolling force, but also improves the plasticity of the iron sheet.

7. In the process of coiling, the coiling temperature is controlled at 500℃-600℃, the structure type can be changed, not only the desired structure can be obtained, but also the cold rolling force caused by the high strength of the hot rolled coil can be avoided. is too big.

In the embodiment of the present invention, the influence of Si, Cr, Mo, P and other elements and their composite effects on the high-temperature oxidation characteristics of strip steel is deeply studied, and a composition system suitable for surface control of cold-rolled high-strength steel is designed. In addition, it is pointed out that the root of the color difference in cold rolling lies in the theory of superficial layer cracking in the cold rolling process of strip steel. The surface roughness generated by the pickling of the hot-rolled red iron sheet and the cracking in the cold rolling process caused by the microstructure characteristics of the material are organically integrated, and a new method is proposed. A series of control measures. In addition, the role of factors such as the inheritance of red scale defects in hot coils, the cooling characteristics of hot coils, and the microstructure characteristics of strip steels in the superficial rolling were investigated, and a control strategy was formulated according to their mechanism of action. Using the embodiment of the present invention, the color difference defect after cold rolling of high-strength steel can be easily removed without increasing equipment. In addition, the embodiments of the present invention also have the advantages of simple method, economical efficiency, strong applicability, and remarkable effect.

Although preferred embodiments of the present invention have been described, additional changes and modifications to these embodiments may occur to those skilled in the art once the basic inventive concepts are known. Therefore, the appended claims are intended to be construed to include the preferred embodiment and all changes and modifications that fall within the scope of the present invention.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention. Thus, provided that these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims (10)

1. a kind of production method of high-strength steel characterized by comprising

Control the component content of steel grade by mass percentage: control Si content adds Cr element in 0.2%- less than 0.3% 0.5%, addition Mo element controls P element and is made steel in 0.01%-0.04%, obtain molten steel in 0.2%-0.5%；

Continuous casting is carried out to obtained molten steel, obtains slab；

Hot rolling is carried out to obtained slab；

Continuous annealing is carried out to the slab after rolling.

2. production method as described in claim 1, which is characterized in that described pair of obtained slab carries out hot rolling, comprising:

The obtained slab is heated, roughing, finish rolling and is batched.

3. production method as claimed in claim 2, which is characterized in that during the heating, tapping temperature is controlled At 1180 DEG C -1200 DEG C, the control of soaking zone time is in 30min-35min, and total time inside furnace control is in 150min-180min.

4. production method as claimed in claim 2, which is characterized in that during the finish rolling, using two pass time de-scaling Technique.

5. production method as claimed in claim 2, which is characterized in that during the finish rolling, between first three rolling-mill housing Cooling water ratio is 50%, and roll gap water opens ratio and reaches 80%.

6. production method as claimed in claim 2, which is characterized in that intensively cold using front end during described batch But mode or ultrafast cold refrigerating mode cool down hot rolled plate.

7. production method as claimed in claim 2, which is characterized in that during described batch, by oiler temperature control At 500 DEG C -600 DEG C.

8. such as production method of any of claims 1-7, which is characterized in that carry out heat in described pair of obtained slab After rolling, further includes:

Pickling is carried out to the slab after hot rolling.

9. production method as claimed in claim 8, which is characterized in that the slab to after hot rolling carry out pickling it Afterwards, further includes:

Cold rolling is carried out to the slab after pickling.

10. production method as claimed in claim 9, which is characterized in that during the pickling, cold rolling is totally depressed Rate controls within 70%.