A method for manufacturing a hot-rolled narrow strip steel of MnB system

Abstract

The application discloses a preparation method of MnB hot-rolled narrow strip steel, the MnB hot-rolled narrow strip steel comprises the following components in percentage by mass: 0.18%<=omega[C]<=0.30%, 0.05%<=omega[Si]<=0.35%, 0.90%<=omega[Mn]<=1.20%, 0.10%<=omega[Cr]<=0.40%, omega[Ni]<=0.30%, omega[Cu]<=0.10%, omega[Mo]<=0.10%, 0.02%<=omega[Ti]<=0.06%, 0.0010%<=omega[B]<=0.0050%, 0.010%<=omega[Al]<=0.050%, omega[O]<=0.0020%, omega[N]<=0.010%, omega[P]<=0.015%, omega[S]<=0.010%; the preparation process of the MnB hot-rolled narrow strip steel comprises the following steps: electric arc furnace smelting, LF furnace refining, VD furnace vacuum degassing, continuous casting, heating, rolling and coiling; the sum of the inclusion rating A+B+C+D coarse system and fine system is less than or equal to 4.5, the banded structure is less than or equal to 2.0, the decarburization layer depth is less than or equal to 1% D (D is the product thickness, mm), the requirements of a user for the cleanliness, banded structure and decarburization layer of the MnB hot-rolled narrow strip steel are met, the product index requirements of the MnB hot-rolled narrow strip steel are met, and additional equipment and processes are not needed.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of MnB system hot-rolled narrow strip steel. BACKGROUND

[0002] Hot-rolled narrow strip steel is not only directly consumed as a sheet, narrow strip steel, but also used as a raw material for cold-rolled sheet, welded pipe, cold-formed steel and other products, and is widely used in the fields of construction, light industry, machinery, textile, automobile, electronics, agricultural machinery and the like. At present, the variety, specification and application field of the narrow strip steel products in China are relatively narrow, and the size precision, surface quality and microstructure performance and other indexes are not high. In recent years, the equipment level of the hot-rolled wide strip steel rolling mill in China is continuously improved, the production scale is gradually expanded, and the production develops very fast. However, compared with the narrow strip, the production cost is relatively high, and there are different views on whether the narrow strip product should be eliminated. If the characteristics of the narrow strip steel, such as small size, fullness, low cost and variety, can be fully utilized, and the purpose of developing new products, improving quality and expanding new fields is achieved, through necessary technical reform measures and reasonable adjustment of product structure, the narrow strip steel product will coexist with the wide strip steel for a long time. Therefore, it is urgent to improve the product quality for the survival of the narrow strip steel industry.

[0003] The alloy steel MnB system is a material widely used in key components such as automobile door lock system, safety system and driving system. The narrow strip steel product needs to go through multiple processes such as pickling, cold rolling and stamping forming, and the product has high requirements on banded structure level, decarburization layer depth and purity.

[0004] Banded structure is a structure morphology formed by stacking the banded structure of pro-eutectoid ferrite and the banded structure of pearlite in the rolling direction of the steel, including primary banded structure and secondary banded structure. The primary banded structure is mainly caused by the dendritic segregation due to the selection and crystallization in the pouring process, and the secondary banded structure is mainly affected by the cooling process after rolling. The banded structure makes the transverse plasticity and toughness of the steel decrease, and has an influence on the hardness uniformity of the steel. In the subsequent heat treatment process, the banded structure is prone to deformation and other adverse consequences. The existence of the banded structure makes the microstructure of the steel uneven, and has an adverse effect on the plasticity, impact toughness and section shrinkage of the steel. Therefore, reducing the banded structure level is of great significance to the subsequent processing and use of the product.

[0005] The surface decarburization layer, especially the full decarburization layer, can greatly affect the fatigue life of the product. For the narrow strip steel product, the surface decarburization layer will seriously restrict the utilization rate of the cut edge of the finished strip steel. If the initial decarburization layer of the strip steel is serious, the strip steel needs to increase the cut edge amount after cold rolling and heat treatment to ensure the product quality, which will reduce the effective utilization rate of the material.

[0006] For MnB hot-rolled narrow strip steel, there is almost no one to study the improvement of cleanliness, the reduction of banded structure level, the control of decarburization layer, etc., therefore, it is particularly crucial to explore the exclusive preparation method of MnB hot-rolled narrow strip steel. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a preparation method of MnB hot-rolled narrow strip steel, which meets the requirements of users for the cleanliness, banded structure and decarburization layer of the MnB hot-rolled narrow strip steel, and achieves the product index requirements of the MnB hot-rolled narrow strip steel without the need to increase additional equipment and processes.

[0008] The technical solution of the present application to solve the above technical problems is: a preparation method of MnB hot-rolled narrow strip steel, the MnB hot-rolled narrow strip steel comprises the following components in terms of mass fraction: 0.18%≤ω[C]≤0.30%, 0.05%≤ω[Si]≤0.35%, 0.90%≤ω[Mn]≤1.20%, 0.10%≤ω[Cr]≤0.40%, ω[Ni]≤0.30%, ω[Cu]≤0.10%, ω[Mo]≤0.10%, 0.02%≤ω[Ti]≤0.06%, 0.0010%≤ω[B]≤0.0050%, 0.010%≤ω[Al]≤0.050%, ω[O]≤0.0020%, ω[N]≤0.010%, ω[P]≤0.015%, ω[S]≤0.010%; the preparation process of the above MnB hot-rolled narrow strip steel comprises: electric arc furnace smelting→LF furnace refining→VD furnace vacuum degassing→continuous casting→heating→rolling→coiling.

[0009] The present application further limits the scheme:

[0010] Preferably, the tapping conditions in the electric arc furnace smelting are that the tapping C content is 0.05%, the P content is 0.012%, and the temperature is 1630℃, and the feeding sequence in the tapping process is: deoxidizer→alloy→modified refining slag→lime, and the electric furnace tapping process adds deoxidizer Al block 0.8-1.2kg / t, lime 5-8kg / t, and modified refining slag 2-5kg / t t.

[0011] Preferably, in the LF furnace refining process, the initial Al content is ≥0.02%, the final Al content is ≥0.02%, the amount of added fluorite is 0.4-0.6kg / t, and the diffusion deoxidizer is 0.8-1.2kg / t.

[0012] Preferably, in the VD vacuum treatment degassing process, the ultimate vacuum time is greater than or equal to 12 min, the static stirring time is greater than or equal to 15 min, and Ti and B are alloyed after vacuum.

[0013] Preferably, in the continuous casting process, the superheat is 15-35 DEG C, the casting speed is 0.80-0.90 m / min, and the secondary cooling water is weakly cooled.

[0014] Preferably, in the heating process, a step-by-step heating furnace is used, which is divided into a preheating section, a first heating section, a second heating section, a third heating section and a soaking section, wherein the preheating section has a furnace temperature of less than or equal to 850 DEG C, the first heating section has a furnace temperature of 800-1050 DEG C, the second heating section has a furnace temperature of 950-1100 DEG C, the third heating section has a furnace temperature of 1100-1200 DEG C, the soaking section has a furnace temperature of 1150-1250 DEG C, the residual oxygen is less than or equal to 4%, and the total heating time is less than or equal to 200 min.

[0015] Preferably, in the rolling process, the open rolling temperature is 1050-1200 DEG C, the finish rolling temperature is 860-940 DEG C, the thickness is 4.0-8.0 mm, and the width is 300-440 mm.

[0016] Preferably, in the coiling process, the coiling temperature is 450-650 DEG C.

[0017] The beneficial effects of the present application are: by controlling the C content of the electric furnace tapping and the Al block addition amount after the furnace, the initial oxygen content of the molten steel can be effectively reduced, the molten steel is prevented from being over-oxidized, and the generation space of inclusions is further reduced, in order to better remove the inclusions, the initial Al content and the end point Al content of the LF furnace and the static stirring time are controlled to ensure that the inclusions are fully floated, the electric furnace deoxidation system, the LF refining process, the continuous casting process parameter matching and the controlled rolling and controlled cooling in the rolling process are controlled, the sum of the coarse and fine inclusions of the A+B+C+D grade is less than or equal to 4.5, the banded structure is less than or equal to 2.0 grade, the decarburization layer depth is less than or equal to 1 mm, the product thickness is mm, the cleanliness, banded structure and decarburization layer of the MnB hot rolled narrow strip steel meet the requirements of the user, and the product index requirements of the MnB hot rolled narrow strip steel are met, without the need to increase additional equipment and processes. Embodiment Example

[0018] The embodiment provides a preparation method of MnB system hot-rolled narrow strip steel, the MnB system hot-rolled narrow strip steel comprises the following components in percentage by mass: ω[C]: 0.21%, ω[Si]: 0.25%, ω[Mn]: 1.00%, ω[Cr]: 0.20%, ω[Ni]: 0.02%, ω[Cu]: 0.02%, ω[Mo]: 0.01%, ω[Ti]: 0.04%, ω[B]: 0.0020%, ω[Al]: 0.030%, ω[O]: 0.0010%, ω[N]≤0.005%, ω[P]≤0.010%, ω[S]≤0.003%; and the preparation process of the MnB system hot-rolled narrow strip steel comprises the following steps: electric arc furnace smelting, LF furnace refining, VD furnace vacuum degassing, continuous casting, heating, rolling and coiling.

[0019] In the tapping process of the electric arc furnace smelting, the tapping C content is 0.05%, the P content is 0.012%, and the temperature is 1630 DEG C; and the feeding sequence in the tapping process is: deoxidizer, alloy, modified refining slag and lime; and the deoxidizer Al block, lime and modified refining slag are added in the electric furnace tapping process, and the adding amount is 1.0 kg / t, 7 kg / t and 4 kg / t respectively.

[0020] In the LF furnace refining process, the initial Al content is 0.03%, the final Al content is 0.04%, the fluorite supplement amount is 0.5 kg / t, and the diffusion deoxidizer is 1.0 kg / t.

[0021] In the VD vacuum treatment degassing process, the limit vacuum time is 12 min, the static stirring time is 15 min, and the Ti and B alloying is carried out after vacuum.

[0022] In the continuous casting process, the superheat is 25 DEG C, the drawing speed is 0.85 m / min, and the secondary cooling water adopts a weak cooling mode.

[0023] In the heating process, a step-by-step heating furnace is adopted, and the heating process is divided into a preheating section, a first heating section, a second heating section, a third heating section and a soaking section; the furnace temperature of the preheating section is 750 DEG C, the furnace temperature of the first heating section is 1000 DEG C, the furnace temperature of the second heating section is 1080 DEG C, the furnace temperature of the third heating section is 1180 DEG C, and the furnace temperature of the soaking section is 1200 DEG C; the residual oxygen is less than or equal to 4%, and the total heating time is less than or equal to 180 min.

[0024] In the rolling process, the open rolling temperature is 1120 DEG C, the final rolling temperature is 920 DEG C, the thickness is 7.5 mm, and the width is 303 mm.

[0025] In the coiling process, the coiling temperature is 600 DEG C.

[0026] According to the product characteristics, the special smelting, continuous casting and rolling process has been able to produce in batches, and the equipment capacity can effectively support the process execution of the product. The product inspection is shown in Table 1, the sum of the inclusion rating A+B+C+D coarse and fine system ≤4.5, the banded structure ≤2.0 level, the decarburization layer depth, mm ≤1% D (D is the product thickness, mm), which meets the user's requirements for the cleanliness, banded structure and decarburization layer of the MnB system hot-rolled narrow strip steel.

[0027] In addition to the above embodiments, the present application can also have other implementation manners. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present application.

Claims

1. A method for preparing MnB-based hot-rolled narrow strip steel, characterized in that: The MnB series hot-rolled narrow strip steel comprises the following components by mass fraction: 0.18%≤ω[C]≤0.30%, 0.05%≤ω[Si]≤0.35%, 0.90%≤ω[Mn]≤1.20%, 0.10%≤ω[Cr]≤0.40%, ω[Ni]≤0.30%, ω[Cu]≤0.10%, ω[Mo]≤0.10%, and 0.02%≤ω[Ti]≤0.06%. The following parameters are present: 0.0010%≤ω[B]≤0.0050%, 0.010%≤ω[Al]≤0.050%, ω[O]≤0.0020%, ω[N]≤0.010%, ω[P]≤0.015%, ω[S]≤0.010%; the balance is Fe. The above-mentioned MnB series hot-rolled narrow strip steel preparation process includes: electric arc furnace smelting → LF furnace refining → VD furnace vacuum degassing → continuous casting → heating → rolling → coiling. In the continuous casting process, the superheat is 15-35℃, the casting speed is 0.80-0.90m / min, and the secondary cooling water adopts a weak cooling mode. The heating process uses a walking beam furnace, which is divided into a preheating section, a first heating section, a second heating section, a third heating section, and a soaking section. The furnace temperature in the preheating section is ≤850℃, the furnace temperature in the first heating section is 800-1050℃, the furnace temperature in the second heating section is 950-1100℃, the furnace temperature in the third heating section is 1100-1200℃, the furnace temperature in the soaking section is 1150-1250℃, the residual oxygen is ≤4%, and the total heating time is ≤200min. The initial rolling temperature in the rolling process is 1050-1200℃, the final rolling temperature is 860-940℃, the thickness is 4.0-8.0mm, and the width is 300-440mm; the coiling temperature in the coiling process is 450-650℃.

2. The method for preparing MnB-based hot-rolled narrow strip steel according to claim 1, characterized in that: The tapping conditions in the electric arc furnace smelting process are as follows: the C content is 0.05%, the P content is 0.012%, and the temperature is 1630℃. The charging sequence during the tapping process is: deoxidizer → alloy → modified refining slag → lime. During the electric arc furnace tapping process, 0.8-1.2 kg / t of deoxidizer Al blocks, 5-8 kg / t of lime, and 2-5 kg / t of modified refining slag are added.

3. The method for preparing MnB-based hot-rolled narrow strip steel according to claim 1, characterized in that: During the LF furnace refining process, the initial Al content is ≥0.02%, the final Al content is ≥0.02%, the amount of fluorite added is 0.4-0.6 kg / t, and the amount of diffusion deoxidizer is 0.8-1.2 kg / t.

4. The method for preparing MnB-based hot-rolled narrow strip steel according to claim 1, characterized in that: During the vacuum degassing process in the VD furnace, the ultimate vacuum time is ≥12min, the static stirring time is ≥15min, and Ti and B are alloyed after vacuuming.

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