CN104611535A - Cold-rolled steel sheet and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of cold-rolled strip production, and in particular relates to a cold-rolled steel plate and a preparation method thereof. The invention provides a method for preparing a cold-rolled steel plate. The method comprises: hot-rolling, coiling, cold-rolling, annealing, cooling, skin-passing and tension-leveling of the slab in sequence. The annealing method is continuous annealing. In the above-mentioned annealing process, the intermediate slab obtained after cold rolling passes through a heating section, a soaking section, a primary cooling section, an overaging section and a secondary cooling section in sequence, the temperature of the heating section is 790-805°C, and the heating time is 180°C. ~480s; the temperature in the soaking section is 820~850°C, and the soaking time is 60~180s; the end temperatures of the intermediate slab obtained after cold rolling in the primary cooling section, the overaging section and the secondary cooling section are respectively 660 ～690℃, 360～410℃, 420～450℃, the residence time is 50～120s, 10～20, 160～500s respectively. The mechanical properties of the cold-rolled steel plate prepared by the steel plate obtained by the method meet the yield strength of 230-300 MPa, and the cold-rolled steel plate has excellent formability.

Description

A kind of cold-rolled steel plate and preparation method thereof

technical field

The invention belongs to the technical field of cold-rolled strip production, and in particular relates to a cold-rolled steel plate and a preparation method thereof.

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. There are two representative patents for the production of low-carbon steel plates by continuous annealing:

(1) 200910029806.2 Continuous annealing process for deep-drawn and ultra-deep-drawn steel plates

The invention discloses a continuous annealing process for deep-drawing and ultra-deep-drawing steel plates. The steel plates are cleaned before annealing, and then enter a continuous annealing furnace at a speed of 150-350m/min. Nitrogen-hydrogen mixed gas is used to spray the surface of the steel plates to carry out the process on the steel plates. Protect and prevent oxidation, while heating the steel plate to 120-180°C; heat the steel plate again to 750-780°C, and keep it warm for 40-70s; then cool the steel plate to 400-460°C, and keep it warm for 60 ~300s for aging treatment, then cooled to room temperature. Due to the over-aging annealing process, the carbides in the steel are fully analyzed, which ensures the stamping performance and ultra-deep drawing performance of the home appliance steel plate and automobile plate.

(2) 201110052830.5 Low-temperature continuous annealing interstitial-free cold-rolled steel sheet and its production method

The invention discloses a production method of low-temperature continuous annealing interstitial-free cold-rolled steel sheet, which contains C: 0.0005% to 0.0025%, Si: ≤0.030%, Mn: 0.05% to 0.15%, P≤0.015%, S≤0.010%, O ≤ 0.025%, N: ≤ 0.0025%, Al: 0.015-0.050%, Ti: 0.03-0.07%; the rest consists of Fe and trace elements. The continuous annealing temperature is 710-740°C, and the cold rolling reduction rate is ≥80%. By adopting a reasonable chemical composition and a suitable cold rolling reduction rate, reducing the recrystallization temperature and forming a sufficient cold rolling microstructure, it can adapt to a lower continuous annealing temperature, thereby reducing cost and production difficulty.

However, the above method cannot obtain a hot-dip galvanized steel sheet with both strength and formability, and the cost is relatively high.

Contents of the invention

The invention provides a method for preparing an ultra-low carbon cold-rolled steel plate. The mechanical properties of the cold-rolled steel plate obtained by the method meet yield strength 230-300 MPa, tensile strength ≥ 390 MPa, elongation ≥ 38.0%, plasticity The strain ratio r ₉₀ ≥ 1.8 and the work hardening index n ₉₀ ≥ 0.2 meet the requirements of the market with a certain strength and can be stamped and formed.

Technical scheme of the present invention:

The first technical problem to be solved by the present invention is to provide a method for preparing cold-rolled steel plates, which includes: hot-rolling, coiling, cold-rolling, annealing, cooling, skin-passing and tension-leveling of the slab in sequence, wherein :

The coiling temperature is 710-740°C;

The reduction rate of the cold rolling is 70-85%;

The annealing method is continuous annealing. In the annealing process, the intermediate slab obtained after cold rolling passes through a heating section, a soaking section, a primary cooling section, an overaging section, and a secondary cooling section in sequence. The temperature is 790-805°C, and the heating time is 180-480s; the temperature in the soaking section is 820-850°C, and the soaking time is 60-180s; The end temperatures of the secondary cooling section are 660-690°C, 360-410°C, 420-450°C, and the residence times are 50-120s, 10-20, 160-500s;

The composition of the slab is C: 0.0010-0.0060%, Si: ≤0.05%, Mn: 0.50-1.0%, P: 0.06-0.10%, S: ≤0.010%, Ti: 0.01-0.05%, Nb: 0.01 ～0.05%, B: 0.001～0.002%, Als: 0.01～0.06%, the balance is composed of Fe and unavoidable impurities.

Preferably, the hot rolling includes rough rolling and finish rolling, the start rolling temperature of the rough rolling is 1200°C-1230°C, the finish rolling temperature of the rough rolling is 1090-1150°C, and the rough rolling time is 200-300min; The start rolling temperature of the finish rolling is 1000°C-1070°C, and the finish rolling temperature is 910°C-940°C.

Preferably, the rough-rolled intermediate slab has a thickness of 47 mm to 50 mm.

Preferably, the thickness of the finish-rolled intermediate slab is 3-6 mm.

Preferably, the thickness of the cold-rolled sheet obtained after cold rolling is 0.9-1.2 mm.

Preferably, the annealing treatment is carried out in a continuous annealing furnace, and the unit speed of the continuous annealing furnace is 100-200 m/min.

Preferably, the finishing elongation is 0.3-0.7%.

The second technical problem to be solved by the present invention is to provide a cold-rolled steel plate, which is produced by the above-mentioned preparation method of the cold-rolled steel plate.

Further, the yield strength of the cold-rolled steel sheet is 230-300 MPa, the tensile strength is ≥390 MPa, the elongation after fracture is ≥38.0%, the plastic strain ratio r ₉₀ ≥1.8, and the work hardening index n ₉₀ ≥0.2.

Beneficial effects of the present invention:

The mechanical properties of the cold-rolled steel plate prepared by the method of the present invention meet the requirements of yield strength 230-300MPa, tensile strength ≥ 390MPa, elongation after fracture A ₈₀ ≥ 38.0%, plastic strain ratio r ₉₀ ≥ 1.8, work hardening index n ₉₀ ≥ 0.2 Requirements; to meet the market's requirements of a certain strength and can be stamped. In addition, the manufacturing process of the present invention is less difficult to implement, has excellent surface quality and comprehensive performance, and can realize batch production of a high-strength ultra-low carbon steel cold-rolled steel plate on a galvanizing/continuous annealing dual-purpose unit modified by continuous hot-dip galvanizing method.

The invention forms a key technology for producing high-strength ultra-low carbon steel cold-rolled steel sheets on a dual-purpose unit for galvanizing and continuous annealing. After hot-rolling and finish-rolling in the present invention, the method is rapidly cooled to a certain temperature, and then coiled after on-line air-cooling transportation. The rolling process of the invention has simple control and strong adaptability, and the product surface quality is excellent.

Detailed ways

The first technical problem to be solved by the present invention is to provide a method for preparing cold-rolled steel plates, which includes: hot-rolling, coiling, cold-rolling, annealing, cooling, skin-passing and tension-leveling of the slab in sequence, wherein :

The coiling temperature is 710-740°C;

The reduction rate of the cold rolling is 70-85%;

The annealing method is continuous annealing. In the annealing process, the intermediate slab obtained after cold rolling passes through a heating section, a soaking section, a primary cooling section, an overaging section, and a secondary cooling section in sequence. The temperature is 790-805°C, and the heating time is 180-480s; the temperature in the soaking section is 820-850°C, and the soaking time is 60-180s; The end temperatures of the secondary cooling section are 660-690°C, 360-410°C, 420-450°C, and the residence times are 50-120s, 10-20, 160-500s;

The composition of the slab is C: 0.0010-0.0060%, Si: ≤0.05%, Mn: 0.50-1.0%, P: 0.06-0.10%, S: ≤0.010%, Ti: 0.01-0.05%, Nb: 0.01 ～0.05%, B: 0.001～0.002%, Als: 0.01～0.06%, the balance is composed of Fe and unavoidable impurities.

In the present invention, the slab can be prepared by methods known in the art for preparing continuous casting slabs, such as blast furnace ironmaking, molten iron pretreatment, converter smelting, deoxidation in ladle, post-alloying furnace refining, LF electric The continuous casting slab is obtained after heating, RH vacuum treatment and slab continuous casting; the specific preparation conditions are well known in the art.

Wherein, the cooling rate of the primary cooling section is 5-30°C/s; the cooling rate of the secondary cooling section is 40-90°C/s.

Preferably, the hot rolling includes rough rolling and finish rolling, the start rolling temperature of the rough rolling is 1200°C-1230°C, the finish rolling temperature of the rough rolling is 1090-1150°C, and the rough rolling time is 200-300min; The start rolling temperature of the finish rolling is 1000°C-1070°C, and the finish rolling temperature is 910°C-940°C.

In the present invention, the endpoint temperature of the primary cooling section refers to the temperature of the intermediate slab obtained after cold rolling before entering the secondary cooling section through the primary cooling section; the endpoint temperature of the overaging section refers to the temperature obtained after cold rolling The temperature when the intermediate slab passes through the overaging section and enters the final cooling section. The terminal temperature of the secondary cooling section refers to the temperature of the intermediate slab obtained after cold rolling before entering the overaging section through the secondary cooling section.

Further, in the preparation method of the present invention, the steel plate is cleaned after cold rolling, and the cleaning can adopt conventional steel plate cleaning methods in this field, such as alkali cleaning and electrolyte cleaning, the purpose of which is to remove oil stains, oxidized Iron sheet, iron powder and other impurities that affect the surface quality of the steel plate.

In the preparation method of the cold-rolled steel sheet of the present invention, unrestricted process conditions, such as cooling method, cooling rate, heating method, etc., can be conventional techniques in the field.

In order to ensure the stability of its performance and prevent the hardening of the steel plate due to aging within the shelf life, the cold-rolled sheet must be subjected to overaging treatment. The solid solution carbon in the medium reduces the aging performance of the finished steel plate. The temperature of overaging is very important to production. If the temperature is high, the ferrite in the steel after overaging treatment will still dissolve a large amount of carbon, so the overaging treatment will not be added; if the temperature is low, the activity of carbon will be reduced, and it will not be easy to diffuse. .

The second technical problem to be solved by the present invention is to provide a cold-rolled steel plate, which is produced by the above-mentioned preparation method of the cold-rolled steel plate.

The preparation method of the cold-rolled steel plate of the present invention is as follows: desulfurization of molten iron, converter smelting, Ca treatment in LF furnace, RH decarburization, controlling the composition of molten steel within the above range, continuous casting into continuous casting slabs, and heating to 1200°C-1230°C , in the furnace time 200 ~ 300min, rough rolling. The thickness of the hot-rolled intermediate slab is 47mm-50mm, the starting temperature of hot-rolling and finishing rolling is 1000℃～1070℃, and the temperature range of finishing rolling is 910℃～940℃; after finishing rolling, it is cooled to 710℃~ Coiling was performed at 740°C. The thickness of the hot-rolled plate is 3-6 mm. After the hot-rolled plate is cleaned by alkali washing, it is determined to be 70% to 85% in combination with the capacity of the cold rolling mill. After rolling, the unit speed of the coil in the continuous annealing furnace is 100-200m/min, and the steel plate is heated to 820-850°C in the soaking section; the temperature of the strip steel at the end of slow cooling, the end of rapid cooling, and the end of overaging in the continuous annealing furnace They are respectively controlled at 660-690°C, 420-450°C and 360-410°C; the steel strip is cooled to room temperature through a water tank, and skin-passed, and the elongation is controlled at 0.3-0.7%.

The present invention is described in detail below through examples.

In the following examples, the test method of yield strength R _eL , tensile strength R _m , and elongation after fracture A ₈₀ is carried out according to GBT228-2002 metal material room temperature tensile test method; the test method of plastic strain ratio r ₉₀ is carried out according to GBT5027-2007 The determination method of plastic strain ratio of metal material sheet and strip is carried out; the test method of work hardening index n ₉₀ ≥ is carried out according to GBT5028-2008 test method of tensile strain hardening index of metal material sheet and strip.

Example 1

In the present invention, according to the usual molten iron desulfurization, converter smelting, LF furnace Ca treatment, RH decarburization, continuous casting into a continuous casting slab as a slab, the weight percentage of the chemical composition is: C: 0.002%, Si: 0.02%, Mn: 062 %, P: 0.075%, S: 0.003%, Ti: 0.025%, Nb: 0.020%, B: 0.001; Als: 0.030%, and the balance is composed of Fe and unavoidable impurities.

Heating the slab to 1219°C for rough rolling, the rough rolling time is 225min, the thickness of the middle slab after rough rolling is 47mm, and then the rough rolled middle slab is finished rolling, the finish rolling start temperature is 1048°C, the finish rolling The finish rolling temperature is 925° C., and the thickness of the intermediate slab after finish rolling is 5.0 mm; after finish rolling, the slab is cooled to 723° C. for coiling. Combined with the ability of the cold rolling mill, it is cold rolled to a cold rolled sheet thickness of 1.2mm at a cold rolling reduction rate of 76% on the cold rolling mill. Subsequently, the cold-rolled plate is annealed in a continuous annealing furnace. The unit speed of the annealing furnace is 130m/min, and the steel plate is heated to 835°C for 120s in the heating section; The temperature of the end point (secondary cooling section) and the strip steel at the end of overaging are controlled at 675°C, 436°C and 388°C respectively; the skin-pass elongation is controlled at 0.45%.

The yield strength, tensile strength, elongation, r ₉₀ , and n ₉₀ of the obtained ultra-low carbon cold-rolled steel sheet were 245MPa, 405MPa, 42.0, 0.22, and 2.0, respectively.

Example 2-3

The composition percentage of the slab is as shown in Table 1, and the specific process conditions are as shown in Tables 2 and 3; other methods are the same as in Example 1. The mechanical properties of the finished product are shown in Table 4.

Table 1 Chemical composition of slabs

Comparative example 1

The composition percentage of the slab is shown in Table 1, which is not within the scope of the present invention; the specific process conditions are the same as in Example 3; other methods are the same as in Example 1. The mechanical properties of the finished product are shown in Table 4.

Comparative example 2

The composition percentage of the slab is the same as in Example 3, as shown in Table 1; the specific process conditions are as shown in Tables 2 and 3, which are not within the scope of the composition of the present invention; other methods are the same as in Example 1. The mechanical properties of the finished product are shown in Table 4.

Table 2 Hot rolling process conditions

Table 3 Annealing process conditions

Table 4 The performance of the finished product of embodiment and comparative example

Claims (9)

1. a preparation method for cold-rolled steel sheet, the method comprises: by slab successively through hot rolling, batch, cold rolling, annealing, cooling, polishing and straightening, it is characterized in that,

Described coiling temperature is 710 ~ 740 DEG C;

Described cold rolling draft is 70 ~ 85%;

The mode of described annealing is continuous annealing, in described annealing process, the intermediate slab obtained after cold rolling is successively through heating zone, soaking zone, cooling section, overaging section and a cooling twice section, and the temperature of described heating zone is 790 ~ 805 DEG C, heat-up time 180 ~ 480s; The temperature of soaking zone is 820 ~ 850 DEG C, soaking time 60 ~ 180s; The intermediate slab obtained after cold rolling is respectively 660 ~ 690 DEG C, 360 ~ 410 DEG C, 420 ~ 450 DEG C in the terminal temperature of a described cooling section, overaging section and cooling twice section, the residence time be respectively 50 ~ 120s, 10 ~ 20,160 ~ 500s;

Described slab consist of C:0.0010 ~ 0.0060%, Si :≤0.05%, Mn:0.50 ~ 1.0%, P:0.06 ~ 0.10%, S :≤0.010%, Ti:0.01 ~ 0.05%, Nb:0.01 ~ 0.05%, B:0.001 ~ 0.002%, Als:0.01 ~ 0.06% surplus is Fe and inevitable impurity composition.

2. the preparation method of cold-rolled steel sheet according to claim 1, it is characterized in that, described hot rolling comprises roughing and finish rolling, and the start rolling temperature of described roughing is 1200 DEG C ~ 1230 DEG C, the finishing temperature of described roughing is 1090-1150 DEG C, roughing time 200 ~ 300min; The start rolling temperature of described finish rolling is 1000 DEG C ~ 1070 DEG C, and the finishing temperature of described finish rolling is 910 DEG C ~ 940 DEG C.

3. the preparation method of cold-rolled steel sheet according to claim 1 and 2, is characterized in that, the thickness of the intermediate slab after described roughing is 47mm ~ 50mm.

4. the preparation method of the cold-rolled steel sheet according to any one of claims 1 to 3, is characterized in that, the thickness of the intermediate slab after described finish rolling is 3 ~ 6mm.

5. the preparation method of the cold-rolled steel sheet according to any one of Claims 1 to 4, is characterized in that, cold rolling rear gained cold-reduced sheet thickness be 0.9 ~ 1.2mm.

6. the preparation method of the cold-rolled steel sheet according to any one of Claims 1 to 5, is characterized in that, anneal is carried out in continuous annealing furnace, and the unit speed of described continuous annealing furnace is 100 ~ 200m/min.

7. the preparation method of the cold-rolled steel sheet according to any one of Claims 1 to 5, is characterized in that, described polishing unit elongation is 0.3 ~ 0.7%.

8. a cold-rolled steel sheet, is characterized in that, it is obtained by the preparation method of above-mentioned cold-rolled steel sheet.

9. cold-rolled steel sheet according to claim 8, is characterized in that, the yield strength of described cold-rolled steel sheet is 230 ~ 300MPa, tensile strength>=390MPa, elongation after fracture>=38.0%, plastic strain ratio r ₉₀>=1.8, work hardening exponent n ₉₀>=0.2.