CN104372151B - There is excellent surface quality and the cold-rolled steel sheet of processability and production method thereof - Google Patents

Abstract

The invention provides a cold-rolled steel plate with good surface quality and formability and a production method thereof. The composition of the cold-rolled steel sheet is calculated by weight percentage: C 0.001-0.003%, Si≤0.03%, Mn 0.10-0.25%, P 0.003-0.009%, S 0.003-0.008%, N 0.001-0.003%, Ti0. 045~0.085%, Als 0.020%~0.070%, the balance is Fe and unavoidable impurities, and its yield strength is 120~150MPa, tensile strength is 280~320MPa, elongation ≥45.0%, r ₉₀ ≥2.6, n ₉₀ ≥ 0.25, ≥0.25, △n≤0.005, △r≤0.25, the surface quality is above O4 surface. The cold-rolled steel sheet of the present invention is particularly suitable for use as an automobile panel.

Description

Cold-rolled steel sheet with good surface quality and formability and production method thereof

technical field

The invention belongs to the technical field of cold-rolled strip production, in particular to a production method of cold-rolled steel strips with excellent surface quality and formability.

Background technique

With the continuous development of the automobile industry, the market's requirements for automotive sheets continue to increase. Under the premise of ensuring the stamping performance, it also needs to have a certain strength to achieve the goal of reducing costs and increasing efficiency.

Therefore, it is necessary to develop cold-rolled steel sheets with high surface quality and excellent formability to meet the market requirements for panels in the automotive field.

Contents of the invention

The object of the present invention is to provide a cold-rolled steel sheet with high surface quality and excellent formability, which is suitable for panel requirements in the automotive field, and a production method thereof.

An aspect of the present invention provides a method of producing a cold-rolled steel sheet having good surface quality and formability. The method includes the following steps in sequence: smelting to obtain the target molten steel, the composition of which is calculated by weight percentage: C: 0.001-0.003%, Si: ≤0.03%, Mn: 0.10-0.25%, P: 0.003 ～0.009%, S: 0.003～0.008%, N: 0.001～0.003%, Ti: 0.045～0.085%, Als: 0.020%～0.070%, the balance is Fe and unavoidable impurities; continuous casting forms continuous casting slab; heating Continuous casting slab to 1200℃～1230℃; rough rolling to obtain intermediate slab with thickness between 47mm and 52mm; finish rolling to obtain hot rolled plate with thickness between 3mm and 5mm, and the starting temperature of finish rolling is 1000 ℃～1070℃, the temperature range of final rolling is 900℃～930℃; the hot-rolled sheet is cooled to 680～720℃ by laminar flow cooling method for coiling; cold rolling is carried out after alkali washing, and the rolled coil is obtained, among which, The cooling reduction rate is controlled at 70% to 80%; the rolled coil passes through the heating section and the soaking section of the continuous annealing furnace sequentially, wherein the heating section heats the rolled coil temperature to 730-770°C, and the soaking section heats the rolled coil The coil temperature is heated to 810-850°C; after rolling, the strip steel of the rolled coil passes through the air-jet cooling section of the continuous annealing furnace, the entrance of the vertical overaging furnace, the outlet of the vertical overaging furnace and the outlet of the secondary cooling section, among which, the air-jet cooling The temperature of the strip steel in the section is controlled at 210-280°C, the temperature of the strip steel at the entrance of the vertical overaging furnace is controlled at 250-370°C, and the temperature of the strip steel at the exit of the vertical overaging furnace is controlled at 240-300°C. The temperature of the steel strip at the outlet of the secondary cooling section is controlled at 60-100°C; the steel strip is cooled to room temperature through a water tank, and then skin-passed and stretched and leveled. The elongation is controlled within the range of 0.1-0.3%.

Another aspect of the present invention provides a cold-rolled steel sheet having good surface quality and formability. The composition of the cold-rolled steel sheet is calculated by weight percentage: C: 0.001-0.003%, Si: ≤0.03%, Mn: 0.10-0.25%, P: 0.003-0.009%, S: 0.003-0.008%, N: 0.001 ～0.003%, Ti: 0.045～0.085%, Als: 0.020%～0.070%, the balance is Fe and unavoidable impurities, and the yield strength of the cold rolled steel plate is 120～150MPa, the tensile strength is 280～320MPa, Elongation ≥ 45.0%, r ₉₀ ≥ 2.6, n ₉₀ ≥ 0.25, △n≤0.005, △r≤0.25, the surface quality is above O4 surface.

Description of drawings

Fig. 1 shows the microstructure of the finished cold-rolled steel sheet produced by the method for producing cold-rolled steel sheet of the present invention.

detailed description

Hereinafter, the cold-rolled steel sheet having good surface quality and formability and the production method thereof of the present invention will be described in detail with reference to exemplary embodiments.

In an exemplary embodiment of the present invention, a method of producing a cold-rolled steel sheet is accomplished by the following steps performed in sequence.

(1) The target molten steel is obtained by smelting, and the composition of the target molten steel is calculated by weight percentage: C: 0.001-0.003%, Si: ≤0.03%, Mn: 0.10-0.25%, P: 0.003-0.009%, S: 0.003 ～0.008%, N: 0.001～0.003%, Ti: 0.045～0.085%, Als: 0.020%～0.070%, and the balance is Fe and unavoidable impurities. For example, steps such as desulfurization, converter smelting, LF furnace Ca treatment, and RH decarburization can be performed on molten iron to control the composition of molten steel within the composition range required by the target molten steel.

(2) Continuous casting, hot rolling

A continuous casting strand is formed by continuous casting. Subsequently, the continuous casting slab is heated to 1200°C to 1230°C; rough rolling is carried out, and the rough rolling adopts 5 passes of rolling, and all 5 passes are descaled, and rough rolling is obtained to obtain an intermediate slab with a thickness between 47mm and 52mm; Rolling, the starting temperature of controlled finish rolling is 1000℃～1070℃, and the temperature range of finishing rolling is 900℃～930℃, so as to ensure that the hot rolling can obtain a fine structure, and the finishing rolling can obtain a hot-rolled plate with a thickness between 3mm and 5mm. . The hot-rolled sheet is cooled to 680-720°C by laminar flow cooling method for coiling.

(3) cold rolling

After alkali cleaning, cold rolling is carried out, and the cooling reduction rate is controlled at 70% to 80%, so as to obtain rolled coils.

(4) Continuous heat treatment

The rolled coil passes through the heating section and the soaking section of the continuous annealing furnace sequentially, wherein the heating section heats the rolled coil temperature to 730-770°C, and the soaking section heats the rolled coil temperature to 810-850°C, for example, heating The sum of time and soaking time can be controlled to 50-150 seconds; the strip steel of rolled coils passes through the jet cooling section of the continuous annealing furnace, the inlet of the vertical overaging furnace, the outlet of the vertical overaging furnace and the outlet of the secondary cooling section in sequence , wherein the temperature of the strip steel in the jet cooling section is controlled at 210-280°C, the temperature of the strip steel at the entrance of the vertical overaging furnace is controlled at 250-370°C, and the temperature of the strip steel at the exit of the vertical overaging furnace is controlled at 240°C ~300°C, the strip temperature at the outlet of the secondary cooling section is controlled to 60~100°C. For example, the residence time of the strip steel in the jet cooling section of the continuous annealing furnace, the inlet of the vertical overaging furnace, the outlet of the vertical overaging furnace and the outlet of the secondary cooling section can be 30-80s, 30-60s, 260-480s in sequence , 60~100s, 240~300s, 120~180s.

(5) Finishing and straightening

The steel strip is cooled to room temperature through a water bath, and then skin-passed and tension-leveled, wherein the skin-pass elongation is controlled within the range of 0.4-0.7%, and the tension-leveling elongation is controlled within the range of 0.1-0.3%.

In another exemplary embodiment of the present invention, the composition of the target molten steel is preferably: C: 0.0015-0.0025%, Si: 0.01-0.02%, Mn: 0.15-0.20%, P: 0.003-0.009%, S : 0.003-0.008%, N: 0.001-0.003%, Ti: 0.060-0.070%, Als: 0.035%-0.060%, and the balance is Fe and unavoidable impurities.

The cold-rolled steel sheet produced according to the above method has the following components by weight percentage: C: 0.001-0.003%, Si: ≤0.03%, Mn: 0.10-0.25%, P: 0.003-0.009%, S: 0.003-0.008 %, N: 0.001～0.003%, Ti: 0.045～0.085%, Als: 0.020%～0.070%, the balance is Fe and unavoidable impurities; the relevant conditions of its mechanical properties are: yield strength is 120～150MPa, tensile strength 280~320MPa, elongation ≥ 45.0%, plastic strain ratio r ₉₀ ≥ 2.6, work hardening index n ₉₀ ≥ 0.25, weighted average work hardening index Work hardening exponent anisotropy △n≤0.005, plastic strain ratio weighted average The plastic strain ratio anisotropy degree △r≤0.25, and its surface quality is above O4 surface. Among them, O4 is the surface quality judgment, which is SG7A grade, which is equivalent to FC grade. No obvious defects on the surface of the steel plate are allowed, and inclusions are allowed within 10m from the head and tail, and no more than 8 strips are allowed in the middle of the steel coil, inclusions without broken skin; pressed into the iron sheet : Less than 2 pieces within 1 meter, no larger than rice grains, no hand feel.

Exemplary embodiments of the present invention are described below in conjunction with specific examples.

Example 1

Desulfurization of molten iron, converter smelting, Ca treatment in LF furnace, RH decarburization, followed by continuous casting to form continuous casting slabs. The chemical composition of the continuous casting slab by weight percentage is: C: 0.002%, Si: 0.01%, Mn: 0.14%, P: 0.004%, S: 0.005%, N: 0.002%, Ti: 0.058%, Al: 0.048 %, the balance is composed of Fe and unavoidable impurities.

The continuous casting slab is heated to 1213°C for rough rolling, and the time in the furnace is 385min. Rough rolling adopts 5-pass rolling, and all 5-pass descaling. The thickness of the intermediate slab after rough rolling is 50mm. The finish rolling start temperature is 1055°C, the finish rolling temperature is 918°C, the coiling temperature is 698°C, and the thickness of the hot rolled plate is 3.75mm.

The reduction ratio of cold rolling was 73.3%, and the thickness of the cold rolled sheet was 1.0mm. After rolling, the steel plate is heated to 756°C and 836°C respectively in the NOF (No Oxidation Furnace) heating section and the RTH (Radiation Tube Heating Furnace) soaking section of the continuous annealing furnace; the sum of the heating time and the soaking time is controlled as 65 seconds. Subsequently, the strip temperatures in the jet cooling section of the continuous annealing furnace, the inlet of the vertical overaging furnace, the outlet of the vertical overaging furnace and the outlet of the secondary cooling section were controlled to 218, 339°C, 242°C and 87°C, respectively. Skin finishing and tension leveling are carried out, and the elongation is controlled at 0.55% and 0.21% respectively.

After testing, the yield strength of the cold-rolled sheet product of this example is 145MPa, the tensile strength is 305MPa, the elongation is 47.5%, n ₉₀ is 0.27, r ₉₀ is 2.8, is 0.26, △n is 0.002, was 2.4, and Δr was 0.19. Fig. 1 shows the microstructure of the finished cold-rolled steel sheet of this example. The finished cold-rolled steel sheet in this example has a 100% ferrite structure, a grain size of grade 9.0, and a surface quality of O5 surface.

Example 2

Smelting molten steel, the target molten steel composition obtained is C: 0.0026%, Si: 0.02%, Mn: 0.22%, P: 0.003%, S: 0.004%, N: 0.002%, Ti: 0.068%, Al: 0.048%, Yu The amount is composed of Fe and unavoidable impurities. Continuous casting forms continuous cast billets.

The continuous casting slab is heated to 1225°C for rough rolling. Rough rolling adopts 5 rolling passes, and all 5 passes are descaled. The thickness of the intermediate slab after rough rolling is 50mm. The finish rolling start temperature is 1035°C, the finish rolling temperature is 925°C, the coiling temperature is 698°C, and the thickness of the hot rolled plate is 4.75mm.

The reduction ratio of cold rolling was 79%, and the thickness of the cold rolled sheet was 1.0 mm. After rolling, the steel plate is heated to 760°C and 825°C respectively in the NOF (No Oxidation Furnace) heating section and the RTH (Radiation Tube Heating Furnace) soaking section of the continuous annealing furnace; the sum of the heating time and the soaking time is controlled as 120 seconds. Subsequently, the strip temperatures in the jet cooling section of the continuous annealing furnace, the inlet of the vertical overaging furnace, the outlet of the vertical overaging furnace and the outlet of the secondary cooling section were controlled to 260, 345°C, 255°C and 80°C, respectively. Skin finishing and tension leveling are carried out, and the elongation is controlled at 0.45% and 0.20% respectively.

After testing, the yield strength of the cold-rolled sheet product of this example is 130MPa, the tensile strength is 295MPa, the elongation is 48.5%, n ₉₀ is 0.28, r ₉₀ is 2.9, is 0.27, △n is 0.003, is 2.5, and Δr is 0.15. The structure is 100% ferrite, the grain size is 9.0, and the surface quality is O5 surface.

In summary, the present invention produces cold-rolled steel sheets with good surface quality and formability, and the cold-rolled steel sheets produced are especially suitable as panels in the automotive field. The relevant properties are: yield strength of 120-150 MPa, tensile Strength is 280～320MPa, elongation ≥45.0%, r ₉₀ ≥2.6, n ₉₀ ≥0.25, △n≤0.005, △r≤0.25, the surface quality is above O4 surface.

Although the invention has been described above with reference to the drawings and exemplary embodiments, it will be apparent to those skilled in the art that various modifications may be made to the above embodiments without departing from the spirit and scope of the claims.

Claims (5)

1. production has the method for cold-rolled steel sheet for excellent surface quality and processability, and its feature exists The following steps that order is carried out are included in, described method:

Smelting obtains target molten steel, and the composition of described target molten steel is by weight percentage: C:0.001～ 0.003%, Si :≤0.03%, Mn:0.10～0.25%, P:0.003～0.009%, S:0.003～0.008%, N:0.001～0.003%, Ti:0.045～0.085%, Als:0.020%～0.070%, surplus is Fe With inevitable impurity；

Continuous casting forms continuous casting billet；

Add hot continuously cast material to 1200 DEG C～1230 DEG C；

Roughing obtains thickness intermediate slab between 47mm～52mm；

Finish rolling obtains thickness hot rolled plate between 3mm～5mm, and wherein, the start rolling temperature of finish rolling is 1000 DEG C～1070 DEG C, finishing temperature scope is 900 DEG C～930 DEG C；

Through section cooling mode, hot rolled plate is cooled to 680～720 DEG C batch；

Carry out cold rolling after alkali cleaning, and obtain roll after roll up, wherein, cooling reduction ratio control be 70%～80%；

After rolling, volume sequentially passes through bringing-up section and the soaking zone of continuous annealing furnace, and wherein, bringing-up section will be rolled up after rolling Temperature is heated to 730～770 DEG C, and soaking zone will be rolled up temperature and be heated to 810～850 DEG C after rolling；

After rolling volume strip steel sequentially pass through the jet cooling section of continuous annealing furnace, vertical overaging stove entrance, Vertical overaging outlet of still and the outlet of cooling twice section, wherein, by the strip temperature control of jet cooling section It is 210～280 DEG C, is 250～370 DEG C by the strip temperature control of vertical overaging stove entrance, by vertical The strip temperature control of overaging outlet of still is 240～300 DEG C, belt steel temperature cooling twice section exported Control is 60～100 DEG C；

Strip steel is cooled to room temperature through water liquid bath, carries out finishing and straightening, wherein, finishing elongation percentage control System is in the range of 0.4～0.7%, and straightening elongation control is in the range of 0.1～0.3%.

Production the most according to claim 1 has the cold-rolled steel sheet of excellent surface quality and processability Method, it is characterised in that the composition of described target molten steel is by weight percentage: C:0.0015～ 0.0025%, Si:0.01～0.02%, Mn:0.16～0.22%, P:0.003～0.009%, S:0.003～ 0.008%, N:0.001～0.003%, Ti:0.060～0.070%, Als:0.035%～0.060%, Surplus is Fe and inevitable impurity.

Production the most according to claim 1 has the cold-rolled steel sheet of excellent surface quality and processability Method, it is characterised in that described roughing uses 5 passes, and every time carries out de-scaling process.

Production the most as claimed in any of claims 1 to 3 has excellent surface quality and molding The method of the cold-rolled steel sheet of performance, it is characterised in that the composition of described cold-rolled steel sheet is by weight percentage For: C:0.001～0.003%, Si :≤0.03%, Mn:0.10～0.25%, P:0.003～0.009%, S:0.003～0.008%, N:0.001～0.003%, Ti:0.045～0.085%, Als:0.020%～ 0.070%, surplus is Fe and inevitable impurity.

Production the most according to claim 4 has the cold-rolled steel sheet of excellent surface quality and processability Method, it is characterised in that the yield strength of described cold-rolled steel sheet is 120～150MPa, tensile strength It is 280～320MPa, percentage elongation >=45.0%, r₉₀>=2.6, n₉₀>=0.25,△n≤0.005、 △ r≤0.25, its surface quality is more than O4 surface.