JPS5933645B2 - Manufacturing method of highly workable ferritic stainless steel sheet with less occurrence of ridging - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A ferritic stainless steel plate for processing requires not only corrosion resistance and workability but also (resistance to) ridging commensurate with the workability.

As is well known, ridging is undulations that appear on the surface of a product after press forming and extend in the rolling direction, and significantly impairs the aesthetic appearance of the product. Since the higher the processing strain, the higher the undulation height of ridging, materials for highly processed applications are naturally required to have stricter (resistance to) ridging than materials for normal processing applications. The present invention is based on a series of new metallurgical phenomena discovered by the inventors (Tetsu to Hagane, 60 (1976) 4,
The present invention relates to a method for manufacturing highly workable ferritic stainless steel that does not generate zinc and is obtained by integrating knowledge regarding 8227).

The new facts discovered by the present inventors are as follows.

(1) According to the various conventional theories regarding the IJ zinc generation mechanism, if we aim for accumulation in a single direction (554) <225>,
An ideal ferritic stainless steel sheet that does not cause ridging and has good deep drawability should be obtained, for example, by annealing the hot rolled sheet in a box furnace after low temperature hot rolling, and then cold rolling annealing twice. Ti-added low CN ferritic stainless steel (Ti: 0.1-085%, C
+N<300ppm) has a sharp (554)<225> texture and excellent deep drawability, but ridging still occurs.

(2) Occurrence of surface undulations during drawing process: In conventional cylindrical drawing process, it was observed that the welding zinc tends to occur on the entire surface of the flange, but (
554) <225> In a steel plate where the accumulation in a single direction is significant, the occurrence is localized in the direction of the flange portion (from the rolling direction of the blank sheet) 450.

(3) Occurrence of surface undulations during uniaxial tension: Conventionally, it has been common knowledge that ridging occurs most prominently during tension in the rolling direction. However, in a steel plate where (554)<225> accumulation is significant in a single direction, the tensile stress occurs most noticeably in the direction of 30 to 45 degrees from the rolling direction. The conventional assumption that ``resinking occurs most noticeably under tension in the rolling direction'' is not necessarily correct. (4) Form of glue zinc generated during uniaxial tension or drawing: As is well known, the conventional type glue zinc is linear undulations parallel to the rolling direction.

{554}<225> The undulations that occur in a steel plate with significant accumulation in a single direction are clearly linear undulations when magnified at low magnification, but compared to the former, the undulations are shorter in length and width; To the naked eye, it gives the impression of rough skin. (5) (1)-(4
) The type of glue zinc mentioned in 15% uniaxial tension or press forming that does not require a high working degree is not very noticeable and can be removed by simple polishing, but press forming with a severe working degree causes severe undulations (height 215 to 20μ or more) and cannot be easily removed.

The present inventors conducted a detailed study on the causes of zinc and the above-mentioned characteristics that appear in steel sheets with developed {554}<225> orientations, and as a result, the following conclusions were reached.

It is well known that the cause of conventional type glue zinc is the presence of a macroscopic ferrite band structure formed during hot rolling and extending in the rolling direction.

This band structure is processed through hot-rolled plate annealing and cold rolling/annealing process.
554}<225>, etc., it has been thought that re-zink can be prevented by replacing the crystal with various recrystallization orientations such as <225>. Incidentally, the basic technical idea of most of the conventional adhesive zinc prevention methods for processes after hot rolling is to eliminate the band structure by recrystallization, so it is important to know how to effectively promote recrystallization. This is the target of the concrete measures. Normal press forming material (usually SUS
In the case of conventional type glue zinc, which is a problem with 43O steel, such measures can be sufficient to prevent it. However, there is a fixed crystallographic relationship, not random, between the macroscopic band orientations formed during hot rolling and these recrystallization orientations. Even if recrystallization is complete, if a certain recrystallization orientation is distributed in a band shape due to some reason, such as the slope conditions during rolling, it will naturally cause zinc, and such a band structure will cause If this develops, the direction dependence of the in-plane tensile force on the sheet surface will be shown to the extent that the adhesive zinc generation is specific to that orientation. The {554}<225> orientation is also one of such recrystallization orientations. In steel sheets where the accumulation in the {554} <225> direction is particularly significant, there is a band structure consisting of two components, (5th edition) (225) and (554) (225), which are symmetrical in the plane perpendicular to the rolling direction. , Zinc is thought to occur based on band-wise shear deformation of each component that occurs during processing, and as a result of calculating the expected and zinc undulation height for this pair of two components, the book shown above was calculated. It turns out that features (2) and (3) of ridging are easily explained. According to the above knowledge, the following two guidelines can be cited as guidelines for preventing new types of glue zinc. (1) Similar to the conventional glue zinc, this ridding also has its roots in macroscopic band structures formed during hot rolling, so it is necessary to thoroughly subdivide and eliminate these by recrystallization in the subsequent process. This method has the same technical philosophy as the conventional adhesive zinc countermeasure. (
2) In the final product (554) (225) and (
554) (225) To avoid extreme accumulation in the orientation and to perform ideal texture control without impairing deep drawability.In this sense, after final annealing, <11x>//N. D. A steel sheet having a fibrous structure is most desirable for both deep drawability and zincability.

Here <111>ZN. D. A fibrous structure is one in which the {Ill} crystal planes, which are favorable for deep drawability, are arranged parallel to the sheet surface, and there is no specific crystal orientation in the rolling direction. The fact that the {111} plane is parallel to the plate surface means that the <111> direction is the normal direction of the plate surface (
=N. D. (Abbreviation for NOMaldirection)
), and it is a structure similar to the orientation of fibers arranged randomly around this direction.
<111>7N. D. It is called fibrous tissue. Based on the above guidelines, the present invention completely eliminates the macroscopic band structure,
And in the final product, <11x>7N. D. The present invention provides a method for producing a highly workable ferritic stainless steel sheet that completely prevents both old and new types of adhesive and zinc generation by developing a fiber structure and has excellent deep drawability.

As a concrete measure, < 11, which can be said to be the most important feature of the present invention.
．． 1>7N. D. As a result of various studies to obtain a fibrous structure, we found that the method of the present invention, that is, C+N: 0.03% or less, Si: 1.0% or less, Mn: 2.0% or less, Cr:
13 to 20%, one or both of Ti and Nb, 0.1 to 0.5% for Ti, and 0.1 to 0 for Nb.
In the process of hot rolling a steel ingot or slab consisting of 68% Fe and unavoidable impurities with the balance being Fe and unavoidable impurities, and annealing it at below 750°C, 0.
1deg. Heating at a temperature increase rate higher than C/SeC, 780
℃ or more and 950℃ or less, held for less than 30 minutes, cooled, followed by intermediate annealing, and intermediate cold rolling reduction rate of 50
If rolling is performed with a final cold rolling reduction of 30 or more and less than 50%, and then final annealing is performed, <Xtx>//
N. It was found that the scales had a markedly developed D-fiber structure.

The details of the present invention will be explained below.

The process of the present invention consists of two steps.

The meaning of performing rapid heating annealing after the first step, hot rolling and winding, is that the present inventors have proposed [Method for producing ferritic stainless steel sheet without generation of zinc] (Japanese Patent Application No. 501, 1437).
18) As shown in J, the aim is to promote recrystallization and almost completely eliminate the macroscopic band structure. With this kind of treatment, conventional type glue zinc is completely prevented,
This alone has a considerable effect on the new type of glue zinc, but what is more important is that by promoting recrystallization in this process, it becomes easier to control the texture in the second step. . The macroscopic band structure should be further fractured in the second stage, that is, the process of two-time cold rolling annealing, but in the case of ferritic stainless steel, generally if cold rolling and recrystallization are repeated by 50% or more, {55
4} <225> direction has a remarkable tendency to accumulate, and as mentioned earlier, this tendency is the cause of a new type of glue zinc. Therefore, simply repeating cold rolling and recrystallization will not produce a new type of glue. It is difficult to completely prevent glue zinc. Ideal texture: <111>//N. D. As shown in the examples, the fiber structure was formed after rapid annealing, with intermediate annealing in between, intermediate cold rolling reduction of 50% or more, and final cold rolling reduction of 3.
It is obtained by rolling 0% or more and less than 50%, and then final annealing. It is desirable that the second stage process be used in combination with the first stage process. This is because if only the second stage process is used, conventional type glue zinc will occur and the effect of completely preventing new type glue zinc will be unstable. The technical concept of this process is to annealing the hot-rolled sheet under rapid heating to crush and finely divide the macroscopic band structure formed during hot rolling as much as possible by recrystallization, and to facilitate texture control in the subsequent process. Then, the cold rolling reduction ratio distribution is made appropriate, and finally the ideal <111>7N. D
．． Obtaining a fibrous tissue ζ (more, secondary arising (55
4) [225) (554>(225)) The object is to eradicate the influence of the band, thereby completely preventing both the conventional quib and the new type of glue zinc.The reasons for the limitations of the present invention will be described below.

The effect of preventing glue and zinc according to the present invention does not originally depend on the ingredients, but the new type of glue and zinc prevention that is a feature of the present invention becomes a practical problem when a high degree of press processing is applied. Therefore, in order to be able to perform high processing, it is necessary to limit the ingredients. That is, C+
If N>300ppI[l, it is difficult to obtain a lower value and ductility that can withstand high-level press working, so it is necessary to suppress C+N to 300ppII1 or less. Regarding the amount of addition of TI and Nb, one or both of T + and Nb was set to 0 for Ti.
．． By adding 1 to 0.5% and 0.1 to 0.8% for Nb, it is possible to obtain a high 7 value, and if either of them is below the lower limit of this range, the high 7 value is However, even if it exceeds the upper limit of this range, no further effect of improving the material quality is found, so it was limited to the above range. Of course, in order to improve the lower value, it is also effective to use other carbide-forming elements other than Ti and Nb. The reasons for the limitations in the method of the present invention will be described below.

Regarding hot rolling, if low-temperature hot rolling is carried out, it is naturally possible to achieve a corresponding effect of preventing glue and zinc, but if the method of the present invention is adopted in the process after hot-rolling, the expected effect will be sufficient. Therefore, the winding temperature of the hot-rolled sheet should be set to over 750°C, which can be done by the normal hot-rolling method, or the temperature range above the winding-up temperature during annealing of the hot-rolled sheet should be set at 0.1 deg, C/
If heated at a temperature increase rate of less than Sec, recrystallization will not be sufficient and the desired adhesive and zinc prevention effect will not be obtained.
It was limited to C/Sec or higher.

Also, if the reached temperature is less than 780°C, complete recrystallization will not occur, and the reached temperature will be over 950°C, or the reached temperature will be 950°C.
If held for more than 30 minutes even below, the crystal grains will become coarser and the zinc prevention effect will be insufficient.
Within minutes. The downstream rate of intermediate cold rolling prior to final cold rolling is 5
The reason why it is set to 0% or more is that once {554}<2
25> This is to develop the recrystallized structure, and the reason why the final cold rolling reduction ratio is set to 30 to 50% is that {5
54} Avoid accumulation in <225> direction, ideal direction: <
111>7N. D. This is to obtain RM1 tissue.

If the final cold rolling reduction is 50% or more or the intermediate cold rolling reduction is 50% or less, the final product will be {554}<225
> direction, or <111>7N. D. This is undesirable as it results in a thick texture with a large amount of dispersion. The effects of the present invention will be explained below using examples.

EXAMPLE A slab whose components are shown in Table 1 was hot rolled (finishing temperature: 780 degrees Celsius) using a continuous annealing furnace at 5 degrees. C/S
Table 2 shows the results of examining the zinc resistance and workability of sheets that were heated with EC, held for 2 minutes after reaching 850°C, and then air-cooled and subjected to various cold rolling and annealing processes shown in Table 2. It is shown in Table 3.

The texture was determined from the {100} pole figure, and the lower value was determined from the plastic strain ratio in tension in directions of 0°, 45°, and 90° from the rolling direction by normal averaging operations. Regarding adhesive zinc properties, considering the characteristics of both old and new types of adhesive zinc, we measured the surface undulations that occurred using a surface roughness meter when tensile deformation of 15 factors was applied in the rolling direction and in a direction 30° from the rolling direction. The results were then comprehensively evaluated. From Table 3, the hot rolled sheet annealing is carried out by rapid heating, the primary cold rolling reduction is more than 50%, and the secondary cold rolling is less than 30%.
It can be seen that when the content is less than 50%, any type of glue zinc can be prevented and workability is not impaired. An example of the texture of the final annealed plate at this time is shown in FIG. For comparison, in treatments J and K in which hot-rolled sheets were annealed in a conventional box-type furnace, conventional glue zinc occurred due to tension in the rolling direction. An example of the texture of the final annealed plate at this time is shown in FIG. As is clear from the explanations so far, the feature of the present invention is that it is most effective in simultaneously preventing both the conventional type of adhesive zinc and the new type of adhesive zinc found in highly formable ferritic stainless steel sheets made by conventional methods. The aim is to provide a method that can be realized easily and efficiently.

Therefore, if this method is adopted to produce a highly formable ferritic stainless steel sheet containing Ti and Nb and reduced in CN, (l) it will be possible to It is possible to prevent both type glue zinc and new type glue zinc. (2) There are no particular problems in the process, but rather there is an advantage of improving productivity by changing hot-rolled sheet annealing from conventional box annealing to rapid short-time heating. .

The effects are enormous. As described above, the present invention is extremely effective as a method for producing a highly workable ferritic stainless steel sheet with little generation of zinc.

[Brief explanation of the drawing]

Figure 1 shows {100} after final annealing of Example steel I treatment D material.
<111>7N. in the pole figure. D. This is an example of one having a fibrous structure.

Claims (1)

[Claims] 1 C+N: 0.03% or less, Si: 1.0% or less, M
n: 2.0% or less, Cr: 13-20%, one or both of Ti and Nb, 0.1-0.5% for Ti, N
A steel ingot or slab containing 0.1 to 0.8% b and the balance Fe and unavoidable impurities is hot-rolled to 750%
0.1 deg. in the temperature range above the winding temperature during the process of rolling it up at a temperature of 0.1°C or higher and annealing it. Heating at a temperature increase rate of C/sec or more, raising the temperature from 780°C to 950°C, 3
After holding for less than 0 minutes, it is cooled, followed by intermediate annealing, rolling with an intermediate cold rolling reduction of 50% or more and a final cold rolling reduction of 30% or more and less than 50%, and then final annealing. te〈1
11〉//N. D. A method for producing a highly formable ferritic stainless steel sheet with less occurrence of ridging, which is characterized by developing a fiber structure.