阅读说明：本技术 一种具有高成形性的if钢及其制备方法 (IF steel with high formability and preparation method thereof ) 是由 王畅 于洋 王林 刘文鑫 张亮亮 高小丽 王泽鹏 李高峰 张栋 刘李斌 陈瑾 于 2020-06-09 设计创作，主要内容包括：本发明属于冶金和轧钢领域,具体涉及一种具有高成形性的IF钢及其制备方法,按质量百分比计,所述IF钢包含C 0.002-0.006％,Si 0.01-0.03％,Al 0.03-0.07％,Ti 0.011-0.05％,S 0.01-0.03％,余量为铁和不可避免的杂质；所述制备方法包括：冶炼并连铸得到钢板坯,将所述钢板坯依次进行加热、粗轧、精轧和卷取,得到钢卷；将所述钢卷依次进行开卷、酸洗、冷轧、退火处理和平整处理,得到所述具有高成形性的IF钢。本发明所述制备方法简单易操作,经济效率高,可以在不增加任何工序和设备的条件下显著提高钢的成形性；本发明结合绿色生产的背景,采用合理的IF钢成分及其含量组成,采用较低的加热温度、较低的退火温度,显著地提高了IF钢的热成形性和力学性能,并降低了IF钢的各向异性。(The invention belongs to the field of metallurgy and steel rolling, and particularly relates to IF steel with high formability and a preparation method thereof, wherein the IF steel comprises, by mass, 0.002-0.006% of C, 0.01-0.03% of Si, 0.03-0.07% of Al, 0.011-0.05% of Ti, 0.01-0.03% of S, and the balance of iron and inevitable impurities; the preparation method comprises the following steps: smelting and continuously casting to obtain a steel plate blank, and sequentially heating, roughly rolling, finely rolling and coiling the steel plate blank to obtain a steel coil; and sequentially carrying out uncoiling, pickling, cold rolling, annealing treatment and flattening treatment on the steel coil to obtain the IF steel with high formability. The preparation method is simple and easy to operate, has high economic efficiency, and can obviously improve the formability of the steel without adding any working procedure and equipment; the invention combines the background of green production, adopts reasonable IF steel components and content composition thereof, adopts lower heating temperature and lower annealing temperature, obviously improves the hot formability and mechanical property of the IF steel, and reduces the anisotropy of the IF steel.)

1. An IF steel having high formability, comprising, in mass percent: 0.002-0.006% of C, 0.01-0.03% of Si, 0.03-0.07% of Al, 0.011-0.05% of Ti, 0.01-0.03% of S, and the balance of iron and inevitable impurities.

2. The IF steel with high formability according to claim 1, wherein the IF steel with high formability comprises, in mass percent: 0.004% of C, 0.025% of Si, 0.055% of Al, 0.032% of Ti, 0.01% of S, and the balance of iron and inevitable impurities.

3. The IF steel with high formability according to claim 1 or 2, wherein a {111} texture ratio of the IF steel with high formability is 75 to 85%;

preferably, the IF steel with high formability has a {111} texture ratio of 78.1 to 82.2%.

4. The production method of an IF steel having high formability according to any one of claims 1 to 3, comprising: smelting and continuously casting to obtain a steel plate blank, and sequentially heating, roughly rolling, finely rolling and coiling the steel plate blank to obtain a steel coil; sequentially carrying out uncoiling, pickling, cold rolling, annealing treatment and flattening treatment on the steel coil to obtain the IF steel with high formability;

wherein:

in the process of heating the steel plate blank, the steel plate blank is heated to 1100-1140 ℃, preferably 1140 ℃.

5. The method for preparing IF steel with high formability according to claim 4, wherein the heating the steel slab to a temperature of 1100-1140 ℃ comprises: heating the steel plate blank to 1100-1140 ℃, and then keeping the temperature for 20-30 min; preferably for 25 min.

6. The method for producing the IF steel having high formability according to claim 4 or 5, wherein the finish rolling temperature of the rough rolling is 1050-1080 ℃.

7. The method of manufacturing the IF steel having high formability according to claim 4 or 5, wherein the finish rolling is performed at a rolling start temperature of 1030 ℃;

preferably, the finish rolling temperature of the finish rolling is 930-960 ℃, and preferably 950 ℃;

preferably, the rolling speed of the finish rolling is 8-12 m/s.

8. The method of producing the IF steel having high formability according to claim 4 or 5, wherein the thickness of the steel slab before the rough rolling is 250 mm;

preferably, the thickness of the steel plate blank after rough rolling is 35-38 mm.

9. The method for preparing IF steel with high formability according to claim 4 or 5, wherein the coiling temperature is 700-740 ℃;

preferably, the temperature of the annealing treatment is 780-820 ℃, preferably 800 ℃.

10. The IF steel with high formability produced by the method for producing IF steel with high formability according to any one of claims 4 to 9.

Technical Field

The invention belongs to the field of metallurgy and steel rolling, and particularly relates to IF steel with high formability and a preparation method thereof.

Background

IF steel is also called interstitial-free steel, wherein C, N atoms in the steel are fixed into carbide and nitride by adding certain amounts of Ti and Nb because of low C, N content, so that interstitial atoms do not exist in the steel, and the IF steel is called interstitial-free steel. The IF steel has the characteristics of high plasticity, low anisotropy (r), high work hardening index (n), no aging property and the like, and particularly has excellent deep drawing performance, so that the IF steel is widely applied to industries such as automobile manufacturing and the like as a third-generation deep drawing steel plate. In the production of IF steel, carbon and nitrogen compounds in the process of solidification and cooling of molten steel are precipitated from the matrix due to the decrease in solubility with temperature, forming precipitates (second phase particles). The precipitates not only directly determine the degree of clearance of interstitial atoms, but also affect the recrystallization behavior of the steel sheet. Coarse precipitates can be used as nucleation particles of crystal grains to promote recrystallization in the annealing process, and fine precipitates prevent the migration and growth of crystal boundaries in the recrystallization process, so that the development of the IF steel texture is influenced, and the anisotropy (r value) of the steel plate is reduced. Therefore, the precipitates have an important influence on the properties of the IF steel.

It is found that main force for fixing C, N atoms in IF steel is mainly Ti, Nb and other elements. In addition, there may be TiS and Ti in the steel₄C₂S₂These are present as carbon-sulfur compounds. This makes it possible to recognize that the element S has a positive effect on the immobilization of C.

In view of the above, there is a need to develop an IF steel having high formability.

Disclosure of Invention

In view of the above problems, the present invention provides an IF steel having high formability and a method for producing the same. The preparation method is simple and easy to operate, has high economic efficiency, and can obviously improve the formability of the steel without adding any working procedure and equipment; the invention combines the background of green production, adopts reasonable IF steel components and content compositions thereof, adopts lower heating temperature and lower annealing temperature, obviously improves the hot formability and mechanical property of the IF steel, increases the work hardening index (n), increases the plastic strain ratio (r value) of the IF steel, and reduces the change of the delta r value (representing various anisotropy) of the obtained IF steel finished product, wherein the delta r is less than 0.5.

The technical scheme for realizing the purpose is as follows:

the invention provides an IF steel with high formability, which comprises the following components in percentage by mass: 0.002-0.006% of C, 0.01-0.03% of Si, 0.03-0.07% of Al, 0.011-0.05% of Ti, 0.01-0.03% of S, and the balance of iron and inevitable impurities.

In one embodiment, the IF steel with high formability according to the present invention comprises, in mass percent: 0.004% of C, 0.025% of Si, 0.055% of Al, 0.032% of Ti, 0.01% of S, and the balance of iron and inevitable impurities.

The production method of the present invention appropriately promotes coarsening of precipitates during rough rolling and finish rolling by controlling the content of the S element.

In one embodiment, in the IF steel with high formability according to the present invention, the ratio of {111} texture in the IF steel with high formability is 75 to 85%; preferably, the IF steel with high formability has a {111} texture ratio of 78.1 to 82.2%. The {111} texture ratio of the IF steel having high formability contributes to an increase in the work hardening index (n) and the plastic strain ratio (r-value) of the IF steel.

The invention also provides a preparation method of the IF steel with high formability, which comprises the following steps: smelting and continuously casting to obtain a steel plate blank, and sequentially heating, roughly rolling, finely rolling and coiling the steel plate blank to obtain a steel coil; sequentially carrying out uncoiling, pickling, cold rolling, annealing treatment and flattening treatment on the steel coil to obtain the IF steel with high formability;

wherein:

in the process of heating the steel plate blank, the steel plate blank is heated to 1100-1140 ℃, preferably 1140 ℃. The invention adopts a heating furnace process with the temperature of 1100-1140 ℃ to prevent the re-dissolution of coarse precipitates generated in the continuous casting process.

In one embodiment, the method for preparing IF steel with high formability according to the present invention, wherein the heating of the steel slab to a temperature of 1100-1140 ℃, preferably 1140 ℃, comprises: and heating the steel plate blank to 1100-1140 ℃, and then keeping for 20-30 min, preferably 25 min.

In one embodiment, in the method for producing IF steel having high formability according to the present invention, the finish rolling temperature of the rough rolling is 1050-.

In one embodiment, in the method for manufacturing IF steel having high formability according to the present invention, the finish rolling start temperature is 1030 ℃; preferably, the finish rolling temperature of the finish rolling is 930-960 ℃, and preferably 950 ℃;

preferably, the rolling speed of the finish rolling is 8-12 m/s.

According to the invention, based on the steps of rough rolling and finish rolling, the generated coarse precipitates can reduce the required annealing temperature, so that the purposes of energy conservation and consumption reduction are achieved, meanwhile, the difference of r values of the IF steel in different directions can be reduced, the difference of all directions of the steel plate is reduced, and the formability is improved.

In one embodiment, in the method for manufacturing IF steel having high formability according to the present invention, the thickness of the steel slab before the rough rolling is 250 mm;

preferably, the thickness of the steel plate blank after rough rolling is 35-38 mm.

In one embodiment, in the method for preparing the IF steel with high formability according to the present invention, the coiling temperature is 700-740 ℃; preferably, the temperature of the annealing treatment is 780-820 ℃, preferably 800 ℃.

The invention also provides the IF steel with high formability prepared by the preparation method of the IF steel with high formability.

Specifically, the method for producing the IF steel having high formability according to the present invention comprises: sequentially heating, rough rolling (the rough rolling adopts a 1+3 mode), finish rolling, coiling, uncoiling, acid washing, cold rolling, annealing and leveling the steel plate blank.

The invention aims at the analysis of chemical components: the invention adopts a thermal simulation test simulation sample to carry out system analysis, and the precipitate state of the obtained IF steel under a 2000-fold microscope is shown in figure 1 under the coiling condition of the temperature of 700-740 DEG CThe IF steel has a large number of large-size precipitates (the particle size is more than 200 nm) which are distributed in a dispersed state, and the morphology of the precipitates is circular, oval, square and long. The above morphologies can be well distinguished by combining spectral analysis, wherein the square morphologies are mainly TiN or Ti (C, N) precipitates, and the circular and elliptical morphologies are mainly TiS or Ti₄C₂S₂And (4) precipitating. The number of large-size precipitates showed a tendency to increase with increasing S content in the steel composition, the IF steel with a content of 60ppm S at 2000-fold microscope had only 13 large-size precipitates on average, the number of large-size precipitates increased with increasing S content to 100ppm and 140ppm, the number of large-size precipitates increased to 20 or more in the same field of view, and the precipitates with 100-fold 200nm size also showed a tendency to grow. For Ti-IF steel, the composition design of the preparation process is favorable for the precipitation and aggregation growth of C, N-containing compounds, and finally coarse and sparse second-phase particles are formed. Furthermore, the coarse and sparse second phase particles can also improve the deep drawing performance of the IF steel finished product, and avoid various defects such as surface roughness, orange peel, longitudinal lines and the like caused by deterioration and deformation of fine two phase particle pinning grain boundaries. Through system research and a large number of screening tests, the invention discovers that when the content of the S element is controlled at a lower level (less than 100ppm), the IF steel finished product has less coarse precipitates and more fine and dispersedly distributed TiC compounds. Precipitates of this type hinder recrystallization and grain growth during subsequent annealing treatment, which is detrimental to the anisotropy r value of IF steel; as the S content increases to 100ppm or more, a significant increase in large-sized precipitates in the crystal grains is observed. Due to Ti₄C₂S₂The amount of precipitated fine and dispersed TiC is increased, the amount of precipitated fine and dispersed TiC is obviously reduced, and the precipitate control mode is beneficial to subsequent processing.

The invention aims at the control of the process flow: according to the invention, a great deal of research shows that the low heating temperature can reduce the re-dissolution of precipitates in the steel plate blank, so that coarse precipitates can be obtained at the subsequent coiling temperature, and the coarse precipitates have a certain genetic effect after the subsequent cold rolling and annealing treatment, so that the precipitates in an IF steel finished product can be coarsened, the refinement of the precipitates caused by the reduction of the annealing temperature can be compensated to a certain extent, and conditions are created for the reduction of the annealing temperature. As shown in FIG. 2, the results of the precipitates were compared in different combinations of heating temperatures of 1180 ℃ and 1220 ℃ and annealing temperatures of 760 to 840 ℃. It can be seen that at the same heating temperature, as the annealing temperature is increased, the size of the precipitates is increased; at the same annealing temperature, the size of the precipitates increases as the heating temperature decreases. The comparison shows that after the heating temperature is reduced from 1220 ℃ to 1180 ℃, the annealing temperature can be generally reduced by about 20 ℃ under the condition of ensuring that the size of precipitates is not changed. Therefore, the IF steel with high formability is obtained by a large number of screening tests and integrating the product performance requirements, wherein the heating temperature is 1110-1140 ℃ and the annealing temperature is 780-820 ℃.

In addition, the heating temperature is properly reduced, the difference between the rough rolling temperature and the finish rolling temperature of the finish rolling is controlled to be at least less than or equal to 150 ℃, and the rolling speed is limited to be 8-12 m/s, so that the pure rolling time of the strip steel in contact with the rollers is shortened. In general, the pure rolling time can be reduced by 8 seconds by reducing the difference between the rough rolling temperature and the finish rolling temperature by 20 ℃, so the invention selects the following strategy to obtain the target product: the final rolling temperature of the rough rolling is 1050-; the initial rolling temperature of the finish rolling is 1030 ℃, and the final rolling temperature of the finish rolling is 930-960 ℃; and the rolling speed of the finish rolling is 8-12 m/s.

The measurement and evaluation of the IF steel finished product in the invention are as follows: according to the invention, the texture condition of the combined sample with different heating temperatures and annealing temperatures is contrastively analyzed by adopting the scanning electron microscope EBSD function, and especially the proportion of {111} texture which directly influences the stamping performance is concerned. The {111} texture proportion of the IF steel at different annealing temperatures when the heating temperature is 1100 ℃ is shown in FIGS. 3 and 4. It can be seen that, in the case where the heating temperature is 1100 ℃, the {111} texture ratio in the sample is the highest at the annealing temperature of 800 ℃ and reaches 82.2%, and in the remaining cases, the {111} texture ratio in the sample is 75 to 85% or 75 to 78.1%.

The anisotropy analysis of the IF steel product in the invention comprises the following steps: the Δ r values after the annealing temperature was reduced from 830 ℃ to 800 ℃ were compared with different heating temperatures, as shown in Table 1. It can be seen that, under different heating temperatures, the annealing temperature is reduced, so that the delta r value is obviously reduced, the anisotropy of the IF steel product is reduced, and the uniformity is improved. According to the invention, through a large number of screening tests, the product performance requirements are integrated, and the heating temperature is 1100-1140 ℃ and the annealing temperature is 780-820 ℃, so that the IF steel with high formability, small anisotropy and good mechanical property is obtained.

Table 1: delta r value variation of IF steel finished products obtained by reducing different heating temperatures after annealing temperature

Drawings

Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:

FIG. 1 shows the variation of the large-size precipitates obtained according to the present invention with the S element content at a coiling temperature of 700 ℃;

FIG. 2 illustrates the effect of the heating temperature and the annealing temperature on grain size in the present invention;

FIG. 3 shows that the IF steel obtained in the present invention has a {111} texture ratio of 82.2% at a heating temperature of 1100 ℃ and an annealing temperature of 800 ℃;

FIG. 4 shows that the IF steel obtained in the present invention has a {111} texture ratio of 78.1% at the heating temperature of 1100 ℃ and the annealing temperature of 820 ℃.

Detailed Description

The present invention is described in further detail below with reference to specific embodiments, which are given for the purpose of illustration only and are not intended to limit the scope of the invention.

The experimental procedures in the following examples are conventional unless otherwise specified. The raw materials and reagent materials used in the following examples are all commercially available products unless otherwise specified.

The preparation method of the IF steel with high formability comprises the following steps: sequentially heating, rough rolling (the rough rolling adopts a 1+3 mode), finish rolling, coiling, uncoiling, acid washing, cold rolling, annealing and leveling the steel plate blank. Specifically, the method comprises the following steps: smelting and continuously casting to obtain a steel plate blank, and sequentially heating, roughly rolling, finely rolling and coiling the steel plate blank to obtain a steel coil; and sequentially carrying out uncoiling, pickling, cold rolling, annealing treatment and flattening treatment on the steel coil to obtain the IF steel with high formability. Wherein, the invention adopts a heating furnace process with the temperature of 1100-1140 ℃ to prevent the re-dissolution of coarse precipitates generated in the continuous casting process.