CN110343959B

CN110343959B - Ultra-deep drawing hot-dip galvanized steel and preparation method thereof

Info

Publication number: CN110343959B
Application number: CN201910681127.7A
Authority: CN
Inventors: 刘再旺; 尉冬; 李明远; 刘李斌; 陈斌; 王川; 滕华湘; 熊爱明; 梁轩; 李学涛; 郑学斌; 张志敏
Original assignee: Shougang Corp
Current assignee: Shougang Corp
Priority date: 2019-07-25
Filing date: 2019-07-25
Publication date: 2021-02-19
Anticipated expiration: 2039-07-25
Also published as: CN110343959A

Abstract

The invention provides ultra-deep drawing hot-dip galvanized steel which comprises the following chemical components in percentage by weight: c:0.003 to 0.005%, Mn: 0.1-0.3%, Si: less than or equal to 0.01 percent, P: less than or equal to 0.005 percent, S: less than or equal to 0.02 percent, Als: 0.02-0.05%, N: 0.002-0.003%, B: 0.0003 to 0.0009%, Ti: 0.05-0.09%, wherein Mn/S is 10-20, P/B is less than or equal to 13, and the balance is Fe.

Description

Ultra-deep drawing hot-dip galvanized steel and preparation method thereof

Technical Field

The invention relates to the technical field of steel manufacturing, in particular to ultra-deep drawing hot-dip galvanized steel and a preparation method thereof.

Background

The ultra-deep drawing steel is third-generation automobile steel, the category of the steel is interstitial free steel, the content of solid solution elements such as C, N in the steel is reduced to be extremely low mainly through a vacuum degassing technology, a certain amount of alloy elements such as Ti or Nb are added into the steel, and the residual solid solution atoms in the steel are fixed, so that the low yield strength, the high elongation and the high r value are realized, and the ultra-deep drawing steel has good forming performance, is mainly produced by adopting a continuous annealing or continuous hot galvanizing method, and is mainly used for complex forming parts of automobiles and inner plates and outer plates of cars.

The ultra-deep drawing steel plate has pure steel quality, and the bonding force of a grain boundary is greatly reduced, so that the grain boundary fracture phenomenon of the steel plate is easy to occur when the steel plate is deformed at a low temperature and a high speed, particularly, the grain boundary fracture behavior is easy to occur due to the segregation of impurity elements, namely phosphorus and sulfur in the steel, in the grain boundary. The secondary processing embrittlement temperature of the common extra-deep drawing steel plate is above minus 30 ℃, and the automobile steel plate is easy to have brittle failure accidents in winter in northern China and North America, and has serious consequences.

Disclosure of Invention

In view of the above problems, the present invention has been made to provide an ultra-deep drawing hot dip galvanized steel and a method for manufacturing the same that overcome the above problems or at least partially solve the above problems.

The embodiment of the invention provides ultra-deep drawing hot-dip galvanized steel which comprises the following chemical components in percentage by weight: c:0.003 to 0.005%, Mn: 0.1-0.3%, Si: less than or equal to 0.01 percent, P: less than or equal to 0.005 percent, S: less than or equal to 0.02 percent, Als: 0.02-0.05%, N: 0.002-0.003%, B: 0.0003 to 0.0009%, Ti: 0.05-0.09%, wherein Mn/S is 10-20, P/B is less than or equal to 13, and the balance is Fe.

Further, the metallographic structure of the steel is ferrite.

Based on the same invention concept, the embodiment of the invention also provides a preparation method of the extra-deep drawing hot galvanized steel, which comprises the working procedures of hot rolling, cold rolling, hot galvanizing and finishing, wherein in the hot rolling process, the heating temperature is 1100-1300 ℃, the initial rolling temperature is 1000-1050 ℃, the final rolling temperature is 880-950 ℃, and the coiling temperature is 660-750 ℃.

Further, in the cold rolling process, 5 frames are adopted for continuous rolling, and the total rolling reduction rate of the continuous rolling is 75-85%, wherein the first frame rolling reduction rate is 30%, and the last frame rolling reduction rate is 5%.

Further, the hot galvanizing adopts continuous hot galvanizing.

Furthermore, in the hot galvanizing process, a heating section

The temperature is 780-860 ℃, the temperature of the soaking section is 780-860 ℃, the temperature of the slow cooling section is 620-730 ℃, the temperature of the fast cooling section is 450-470 ℃, and the temperature of the zinc pot is 455-465 ℃.

Further, in the finishing process, the elongation is controlled to be constant, and the desirable value range of the elongation is 0.3-0.5%.

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

the ultra-deep drawing hot-dip galvanized steel provided by the embodiment of the invention strictly controls chemical elements in the steel, and generally, for ultra-low carbon steel for deep drawing, the lower the carbon content is, the better the carbon content is, a certain C content is kept in the embodiment, and the trace C can be combined with Ti element to form fine precipitated second-phase particles, nail-rolling grain boundaries, increase the binding force among the grain boundaries and be beneficial to improving the secondary processing brittleness of the steel. In addition, the embodiment strictly controls the content of P, S brittle elements, and Mn and B elements are introduced to react with the brittle elements to counteract the effect of harmful elements, so that the best forming performance is realized and the secondary processing brittleness is improved. Wherein, the P/B is controlled to be less than or equal to 13 because the B element competes with the P element to precipitate in a crystal boundary to reduce the brittleness of finished steel, the effect of reducing the brittle temperature cannot be achieved when the B element is added in a small amount, but the forming performance of the steel can be damaged by the excessively added B element, and meanwhile, the Mn/S is controlled to be 10-20 because the Mn can generate MnS in the ultra-low carbon steel and the ratio of free S element in the steel is reduced to reduce the brittle temperature, but the strength is easy to increase when the Mn content is excessively high, so that the deep drawing is not facilitated.

According to the preparation method of the ultra-deep drawing hot-dip galvanized steel, provided by the embodiment of the invention, the temperature difference in the hot rolling process is improved by controlling the hot rolling heating temperature, the initial rolling temperature, the final rolling temperature and the coiling temperature, so that the crystal grains are refined, the plasticity of the steel is increased, and the grain boundary is strengthened, so that the prepared ultra-deep drawing hot-dip galvanized steel has the property of secondary processing brittleness resistance.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:

FIG. 1 is a structural view of a scanning electron microscope of a hot dip galvanized steel sheet for an automobile, which is resistant to secondary working brittleness and ultra-deep drawing provided by an embodiment of the invention.

Detailed Description

The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.

Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.

Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.

In order to solve the technical problems, the general idea of the embodiment of the application is as follows:

the application provides an ultra-deep drawing hot-dip galvanized steel, and the chemical components of the steel comprise the following components in percentage by weight: c:0.003 to 0.005%, Mn: 0.1-0.3%, Si: less than or equal to 0.01 percent, P: less than or equal to 0.005 percent, S: less than or equal to 0.02 percent, Als: 0.02-0.05%, N: 0.002-0.003%, B: 0.0003 to 0.0009%, Ti: 0.05-0.09%, wherein Mn/S is 10-20, P/B is less than or equal to 13, and the balance is Fe.

In the present application, the metallographic structure of the steel is ferrite.

Based on the same invention concept, the application also provides a preparation method of the extra-deep drawing hot galvanized steel, which comprises the working procedures of hot rolling, cold rolling, hot galvanizing and finishing, wherein in the hot rolling process, the heating temperature is 1100-1300 ℃, the initial rolling temperature is 1000-1050 ℃, the final rolling temperature is 880-950 ℃, and the coiling temperature is 660-750 ℃.

In the cold rolling process, 5 stands are adopted for continuous rolling, and the total rolling reduction rate of the continuous rolling is 75-85%, wherein the first stand rolling reduction rate is 30%, and the last stand rolling reduction rate is 5%.

In the application, the hot galvanizing adopts continuous hot galvanizing.

In the application, in the hot galvanizing process, the temperature of the heating section is 780-doped 860 ℃, the temperature of the soaking section is 780-doped 860 ℃, the temperature of the slow cooling section is 620-doped 730 ℃, the temperature of the fast cooling section is 450-doped 470 ℃, and the temperature of the zinc pot is 455-doped 465 ℃.

In the application, the elongation is controlled to be constant in the finishing process, and the desirable value range of the elongation is 0.3-0.5%.

The secondary processing brittleness resistant ultra-deep drawing hot dip galvanized steel plate provided by the invention strictly controls the content of P, S element. The P element is a brittle element, and segregation thereof at grain boundaries is a main cause of further increase of the embrittlement temperature of ultra-low carbon steel, so that the low-temperature brittleness of the finished steel can be reduced by controlling the P element at an extremely low level as much as possible, while the S element also increases the brittleness of the steel to some extent, and further control is required. The B element competes with the P element in the crystal boundary to precipitate so as to reduce the brittleness of the finished steel, the effect of reducing the embrittlement temperature cannot be achieved when the adding amount of the B element is too small, but the forming performance of the steel can be damaged by the B element which is excessively added, and the comprehensive performance of the steel is best when the P/B is less than or equal to 13 through practice. Mn can generate MnS in the ultra-low carbon steel and reduce the proportion of free S elements in the steel so as to reduce the brittle temperature, but the strength is easy to increase when the Mn content is too high so as to be not beneficial to deep drawing, and the practice shows that the comprehensive performance of the steel is best when Mn/S is 10-20.

The production method of the secondary processing brittleness resistant ultra-deep drawing hot dip galvanized steel plate for the automobile balances the hot rolling heating temperature, the initial rolling temperature, the final rolling temperature and the coiling temperature, moderately improves the temperature difference in the hot rolling process, is beneficial to refining crystal grains, and increases the plasticity of steel and strengthens crystal boundaries. The production method adjusts the soaking temperature, the slow cooling section temperature and the fast cooling section temperature in the hot galvanizing process, the higher soaking temperature is kept in the hot galvanizing technological process, the forming performance can be improved, trace carbides are dissolved, then the fast cooling outlet temperature is reduced, a fine second phase is separated out from grain boundaries in the cooling process, the grain boundary binding force is increased, and the secondary processing brittleness resistance is improved. The finishing elongation set value provided by the invention is small, and a constant elongation control mode is adopted, so that the stability of the yield strength of steel and the low yield ratio are mainly ensured, and the deep drawing performance is facilitated.

The hot-dip galvanized steel plate for the extra-deep drawing automobile and the production method thereof provided by the invention have the characteristics of high forming performance and high secondary processing brittleness resistance by controlling chemical components and optimizing hot rolling, cold rolling and continuous hot galvanizing processes, so that the product quality is improved, and considerable economic benefits can be brought.

The present application will be described in detail with reference to specific examples.

The chemical composition contents (weight percentages,%) of examples 1-8 are shown in table 1, and the corresponding process parameters of the preparation methods of examples 1-8 are shown in table 2.

TABLE 1

TABLE 2

The mechanical properties and the secondary processing brittle transition temperature of the hot dip galvanized steels prepared according to the chemical compositions in table 1 and the process parameters in table 2 were measured, and the results are shown in decay 3.

TABLE 3

Compared with the prior art, the method has the following characteristics:

the yield strength of the extra-deep drawing hot-dip galvanized steel provided by the embodiment of the invention reaches 148MPa, the tensile strength reaches 305MPa, the elongation reaches 47%, the r value reaches 3.05, and the secondary processing embrittlement temperature reaches-65 ℃.

Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such 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 such modifications and variations.

Claims

1. The ultra-deep drawing hot-dip galvanized steel is characterized by comprising the following chemical components in percentage by weight:

0.003 percent of C, 0.008 percent of Si, 0.23 percent of Mn, 0.003 percent of P, 0.02 percent of S, 0.03 percent of Als, 0.0026 percent of N, 0.0008 percent of B, 0.07 percent of Ti, and the balance of Fe and inevitable impurity elements, wherein the Mn/S is 11.5, and the P/B is 3.75;

the metallographic structure of the steel is ferrite;

the preparation method of the ultra-deep drawing hot-dip galvanized steel comprises the working procedures of hot rolling, cold rolling, hot galvanizing and finishing, and is characterized in that in the hot rolling process, the heating temperature is 1290 ℃, the initial rolling temperature is 1050 ℃, the final rolling temperature is 910 ℃, and the coiling temperature is 730 ℃;

in the cold rolling process, 5 frames are adopted for continuous rolling, and the total rolling reduction rate of the continuous rolling is 75%, wherein the first frame rolling reduction rate is 30%, and the last frame rolling reduction rate is 5%;

the hot galvanizing adopts continuous hot galvanizing;

in the hot galvanizing process, the temperature of a heating section is 835 ℃, the temperature of a soaking section is 835 ℃, the outlet temperature of a slow cooling section is 730 ℃, the outlet temperature of a fast cooling section is 460 ℃, and the temperature of a zinc pot is 460 ℃;

in the finishing process, the elongation is controlled to be constant, and the range of the elongation can be taken as 0.5%.