CN115125454A

CN115125454A - Cold-rolled automobile outer plate with low waviness after forming and production method thereof

Info

Publication number: CN115125454A
Application number: CN202210975064.8A
Authority: CN
Inventors: 张露星; 李子涛; 肖洋洋; 马明璐; 顾斌; 陈德顺; 郑笑芳
Original assignee: Maanshan Iron and Steel Co Ltd
Current assignee: Maanshan Iron and Steel Co Ltd
Priority date: 2022-08-15
Filing date: 2022-08-15
Publication date: 2022-09-30
Anticipated expiration: 2042-08-15
Also published as: CN115125454B

Abstract

The invention provides a cold-rolled automobile outer plate with low waviness after forming and a production method thereof, and the cold-rolled automobile outer plate comprises the following components: c: 0.0002 to 0.003 wt%, Si: less than or equal to 0.030 wt%, Mn: 0.08-0.15 wt%, Als: 0.015-0.050 wt%, P is less than or equal to 0.015 wt%, S is less than or equal to 0.015 wt%, Nb and Ti is less than or equal to 0.06 wt%, and the balance is Fe and inevitable impurities. Through the cooperative control of the components design and the processes of steel making, hot rolling, acid rolling and annealing, the waviness of the final finished product after deformation is ensured to be at a lower level due to the fine and uniform structure of the final finished product. After 5 percent plastic deformation, the waviness Wsa is less than or equal to 0.30 mu m, and the plastic has good low-waviness characteristic after forming.

Description

Cold-rolled automobile outer plate with low waviness after forming and production method thereof

Technical Field

The invention belongs to the technical field of cold-rolled automobile steel, and particularly relates to a cold-rolled automobile outer plate with low waviness after forming and a production method thereof.

Background

In recent years, due to the consideration of environmental protection, energy consumption and cost, more and more vehicle enterprises begin to use a short process flow without floating coat, also called as 2C1B process. This results in a decrease in the thickness of the paint film and an increase in the transfer of the surface structure of the steel sheet to the painted surface.

Under the novel coating process, how to realize the control of the low waviness of the steel plate and realize the good appearance quality of the steel plate after forming and painting is a core technology which must be mastered by steel factories. At present, the popular automobiles and the like require that the Wsa is less than or equal to 0.35 mu m under the condition of 5 percent of deformation of the low-waviness outer plate.

The invention discloses a production method of a hot-dip galvanized IF steel plate with controlled surface waviness, which is disclosed by a patent with publication number CN 112538593A published on 3, 23 and 2021, and finally realizes the improvement of surface texture of the hot-dip galvanized IF steel plate after stamping by comprehensive measures of reasonably designing chemical components of the steel plate, adjusting process parameters of hot continuous rolling and annealing process, controlling surface roughness of a finishing roller and the like, thereby meeting the requirements of 2C1B painting process. The waviness Wsa of the steel plate raw plate produced by the method is less than or equal to 0.35 mu m, the waviness value is higher, the waviness value after forming is not disclosed, the possibility that the waviness after forming does not meet the standard requirement exists, and the method does not study the influence of a grain structure on the waviness of a finished product after deformation.

A patent publication No. CN 109022736 a published on 12, 13, 2018 discloses a method for controlling a cold rolling process of an interstitial-free steel continuously-annealed sheet, in which when the carbon content of the interstitial-free steel is in the range of 0.0005-0.0050% by mass, the total reduction amount of the cold rolling is set to 68.0-77.2% for the interstitial-free steel continuously-annealed sheet with a thickness of 0.8mm, and the thickness of the adopted hot rolled coil is 2.5-3.5mm, and the cold rolling is completed in five passes. The method only takes measures aiming at a steel plate with the thickness of 0.8mm, the thickness of the outer plate is basically 0.6-0.8 mm due to the requirement of light weight at present, the influence factors of the waviness are numerous, and the stable control of the low waviness of the formed steel plate is difficult to realize by simply controlling the reduction rate of the acid rolling. The steel-making, hot rolling, acid rolling and annealing processes are cooperatively controlled, so that the waviness of the final finished product after deformation is fine and uniform, and the final finished product is guaranteed to be at a lower level.

Disclosure of Invention

The invention aims to provide a cold-rolled automobile outer plate with low waviness after forming and a production method thereof, which solve the problem that the long wave generated by adopting a floating-coating-free 2C1B coating process at a client is overproof due to overhigh waviness of a steel plate after stamping deformation through component design and a production method, and can greatly improve the vividness of the steel plate after forming and coating.

The specific technical scheme of the invention is as follows:

a cold-rolled automobile outer plate with low waviness after forming comprises the following components in percentage by mass:

c: 0.0002 to 0.003 wt%, Si: less than or equal to 0.030 wt%, Mn: 0.08-0.15 wt%, Als: 0.015-0.050 wt%, P is less than or equal to 0.015 wt%, S is less than or equal to 0.015 wt%, and the balance is Fe and inevitable impurities, the product is an outer plate product, excessive microalloy addition can cause the temperature rise of recovery recrystallization, subsequent annealing needs higher annealing temperature to realize recovery recrystallization, the higher annealing temperature can cause the surface quality of a finished product to be deteriorated, and the increase of the waviness of a steel plate after deformation can be increased, so that Nb + Ti is required to be less than or equal to 0.06 wt%.

The cold-rolled automobile outer plate with low waviness after being formed is fine and uniform in structure crystal grains, the structure is pure ferrite, the grain size level is 8.5-9.5, the waviness Wsa of the product after being plastically deformed by 5% is less than or equal to 0.30 mu m, and the method is more preferably as follows: after 5 percent plastic deformation, the waviness Wsa is less than or equal to 0.26 mu m, and the plastic has good low-waviness characteristic after forming.

The cold-rolled automobile outer panel with low waviness after being formed has the following properties: the yield strength of the product is 140-180 MPa, the tensile strength is 270-350 MPa, and the elongation rate A is ₈₀ Not less than 38, n not less than 0.21, and r not less than 2.1.

The invention provides a production method of a cold-rolled automobile outer plate with low waviness after forming, which comprises the following process flows of: smelting → continuous casting → hot continuous rolling of casting blank → acid pickling and cold rolling → continuous annealing → leveling → finished product.

The smelting comprises the following steps: the method is suitable for smelting in a converter, an electric furnace and an induction furnace to obtain target molten steel;

and (3) continuous casting: continuous casting is adopted to produce a casting blank, and molten steel is formed and rapidly solidified and crystallized under the action of a crystallizer to form a plate blank;

the casting blank hot continuous rolling: carrying out hot rolling on the continuous casting slab to obtain a hot rolling slab; in the hot rolling process, the heating temperature is controlled to be 1160-1200 ℃, and the finishing temperature is controlled to be 930 +/-20 ℃. The adoption of a lower slab heating temperature is beneficial to improving the product forming performance, and the adoption of a higher finish rolling temperature is beneficial to avoiding the generation of mixed crystals caused by rolling in a two-phase region. Subsequently coiling the hot rolled plate blank to obtain a hot rolled steel coil; the coiling temperature is controlled at 630 +/-20 ℃, and relatively fine and uniform hot rolling tissues can be obtained through lower coiling while coarse grain tissues can be prevented from being generated on the surface layer of the strip steel;

acid washing and cold rolling: the method comprises the following steps of (1) sufficiently removing iron oxide scales on the surface of the strip steel by adopting a conventional pickling process, then carrying out cold rolling to the required thickness specification of a finished product, controlling the cold rolling reduction rate to be 78-82%, reducing the proportion of a surface shear texture by adopting a lower acid rolling reduction rate, and reducing the driving force for grain growth and making the grain size of the finished product finer due to lower storage energy in the subsequent annealing process by adopting the lower acid rolling reduction rate;

and (3) continuous annealing: controlling the annealing temperature of the steel plate treated in the acid pickling and cold rolling step to be 780-810 ℃;

leveling: the roughness of a roller used for leveling is controlled to be 1.6-2.5 mu m, the leveling elongation is controlled to be 0.6-1.0%, and the required steel plate is obtained after leveling.

The invention has the following design ideas of components:

c: the most effective strengthening elements are the most economical and strengthening elements. When the content of C is lower, the formability and the welding performance are better; the trace amount of solid solution carbon can enhance the grain boundary strength and improve the secondary processing brittleness, and the forming performance is not facilitated due to the overhigh carbon content. In the present invention, the C content is 0.0002 to 0.003 wt%.

Si: the steel has a strong strengthening effect, but Si is easy to form oxides, which is not beneficial to forming oxide color on the surface after pickling and annealing, so the invention adds little or no Si, and the upper limit is controlled at 0.03 wt%.

Mn: the steel has a solid solution strengthening effect in steel (Mn dissolved in the steel causes lattice distortion, and the lattice distortion increases the resistance of dislocation movement, so that slippage is difficult to perform, the strength and the hardness of alloy steel are increased, and the yield ratio (toughness and plasticity) of the steel is reduced; in addition, the S-containing metal acts on the steel to prevent hot shortness of the steel. In the patent, Mn mainly reacts with S to prevent hot brittleness of steel and simultaneously plays a role in solid solution strengthening, and the upper limit of Mn is controlled to be 0.15%.

And Als: al mainly plays a role in deoxidation in steel, and Al can form AlN precipitation to play a role in refining grains to a certain extent. The ductility of the steel can be improved on the premise of ensuring the strength performance by the existence of a small amount of Al. However, the high Al content tends to cause clogging of the mold, and the cast slab tends to have defects such as cracking, which increases the cost. Therefore, the Al content of the invention is controlled between 0.015 percent and 0.050 percent by weight.

P: the P content in steel should be strictly controlled because the P content is an inevitable harmful impurity in steel and has an adverse effect on the punching property, cold brittleness, secondary work brittleness, and the like of steel.

S: the S content in the steel is strictly controlled, which increases the smelting cost of the steel, so the upper limit of the S content is controlled to be 0.015 percent.

The balance of Fe and inevitable impurity elements, and the less the impurity elements are, the better the method is on the basis of not increasing additional cost.

The invention realizes the fixing function of the interstitial atoms C, N, S by adding Ti and Nb, ensures the complete fixation of the interstitial atoms by controlling the proper addition amount of the Ti and Nb, and does not cause the surface state deterioration and the increase of the waviness after forming because of excessive addition. And because of the addition of Ti, the dissolution of Ti (CN) can occur in the heating process of the hot-rolled plate blank, the dissolution of Ti (CN) can be effectively reduced by adopting lower plate blank heating temperature, and finally the undissolved carbonitride of the finished product is necessarily thicker, thereby being beneficial to the improvement of the r value of the finished product and the deep drawing performance of the product. The addition of Nb is beneficial to refining grains, and the reduction of the increment of waviness after forming is obviously improved.

According to the invention, through composition design and through the cooperative control of the processes of steel making, hot rolling, acid rolling and annealing, the final finished product has a fine and uniform structure, and the waviness after deformation is ensured to be at a lower level. After 5 percent plastic deformation, the waviness Wsa is less than or equal to 0.26 mu m, and the plastic has good low-waviness characteristic after forming.

Drawings

FIG. 1 shows the structure of an exemplary embodiment of a steel according to the present invention;

FIG. 2 shows the structure state of a typical comparative example of the steel of the present invention.

Detailed Description

Example 1 to example 6

A cold-rolled automobile outer plate with low waviness after forming comprises the following components in percentage by mass: as shown in table 1, the balance not shown in table 1 is Fe and inevitable impurities.

TABLE 1 Steel compositions for the examples

The production method of each embodiment comprises the following process flows: smelting → continuous casting → hot continuous rolling of casting blank → acid pickling and cold rolling → continuous annealing → leveling → finished product.

Smelting: the method is suitable for smelting in a converter, an electric furnace and an induction furnace to obtain target molten steel;

the casting blank hot continuous rolling: carrying out hot rolling on the continuous casting slab to obtain a hot rolling slab; in the hot rolling process, the heating temperature is controlled to be 1160-1200 ℃, and the finishing temperature is controlled to be 930 +/-20 ℃. Coiling the hot rolled plate blank to obtain a hot rolled steel coil; the coiling temperature is controlled at 630 +/-20 ℃, and relatively fine and uniform hot rolling tissues can be obtained by lower coiling, and meanwhile, coarse-grained tissues can be prevented from being generated on the surface layer of the strip steel;

acid pickling and cold rolling: the method comprises the following steps of (1) fully removing iron oxide scales on the surface of a strip steel by adopting a conventional pickling process, then cold-rolling to the thickness specification required by a finished product, controlling the cold-rolling reduction rate to be 78-82%, adopting a moderate acid-rolling reduction rate to avoid reduction of the surface layer shear texture proportion caused by a high reduction rate, and simultaneously reducing the driving force of grain growth and making the grain size of the structure of the finished product finer due to lower storage energy in the subsequent annealing process by the moderate acid-rolling reduction rate;

The specific process parameters of each example are shown in Table 2

TABLE 2 production Process parameters of the examples

The above embodiments have been described in detail for the purpose of illustrating the invention and the effect thereof, it should be understood that the above embodiments are only specific embodiments of the invention, and the invention is not limited by the above embodiments, and various modifications, equivalents, improvements and the like, which are within the spirit and principle of the invention or which are made by adopting the technical idea and technical scheme of the invention, are within the protection scope of the invention.

Claims

1. A cold-rolled automobile outer plate with low waviness after being formed is characterized by comprising the following components in percentage by mass:

c: 0.0002 to 0.003 wt%, Si: less than or equal to 0.030 wt%, Mn: 0.08-0.15 wt%, Als: 0.015-0.050 wt%, P is less than or equal to 0.015 wt%, S is less than or equal to 0.015 wt%, Nb and Ti is less than or equal to 0.06 wt%, and the balance is Fe and inevitable impurities.

2. The cold-rolled automobile outer panel with low waviness after being formed according to claim 1, wherein the cold-rolled automobile outer panel with low waviness after being formed is fine and uniform in structure crystal grains, the grain size level reaches 8.5-9.5, and the waviness Wsa of a product after being subjected to 5% plastic deformation is less than or equal to 0.26 μm.

3. The cold-rolled automobile outer panel with low waviness after forming according to claim 1 or 2, wherein the cold-rolled automobile outer panel with low waviness after forming has the following properties: the yield strength of the product is 140-180 MPa, the tensile strength is 270-350 MPa, and the elongation rate A is ₈₀ Not less than 38, n not less than 0.21, and r not less than 2.1.

4. A method for producing a cold-rolled automobile outer panel having a low waviness after forming according to any one of claims 1 to 3, comprising the following steps: smelting → continuous casting → hot continuous rolling of casting blank → acid pickling and cold rolling → continuous annealing → leveling → finished product.

5. The production method according to claim 4, wherein the slab hot continuous rolling: the heating temperature is controlled at 1160-1220 ℃.

6. The production method according to claim 4, wherein the slab hot continuous rolling: the finishing temperature is controlled to be 930 +/-20 ℃, and the coiling temperature is controlled to be 630 +/-20 ℃.

7. The production method according to claim 4, characterized in that the acid pickling cold rolling: and the cold rolling reduction rate is controlled to be 78-82%.

8. The production method according to claim 4, characterized in that the continuous annealing: and controlling the annealing temperature of the steel plate treated in the acid pickling and cold rolling step to be 780-810 ℃.

9. The production method according to claim 4, wherein the flattening: the roughness of the roller for leveling is controlled to be 1.6-2.5 mu m.

10. The production method according to claim 4, wherein the flattening: the leveling elongation is controlled to be 0.6-1.0%.