JPS6053725B2 - Method for manufacturing austenitic stainless steel sheets and steel strips - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing austenitic stainless steel, mainly 18Cr-8Ni stainless steel, and in particular a method for producing an excellent quality steel plate with small anisotropy even if hot-rolled plate annealing is omitted. It's about how to get it.

Generally, in the production of thin austenitic stainless steel sheets mainly made of 18Cr-8Ni, hot strips are produced using a hot rolling mill such as a hot strip mill.
After that, the hot-rolled sheet is softened and annealed at a high temperature of 1000°C or higher, descaled, and then cold-rolled once or twice with intermediate annealing to form a thin sheet, and finally annealed.
A cold-rolled sheet was produced by pickling. Hot-rolled sheet annealing and descaling are performed on a line unique to stainless steel called the HAP line. With the aim of omitting this hot-rolled sheet annealing, the present inventors have studied in detail the role played by the hot-rolled sheet annealing process. As a result, (1) the hot-rolled sheet is sufficiently recrystallized and softened as a raw material for cold rolling.

(2) Carbides precipitated during hot rolling and coiling are dissolved.

(3) Improve pickling speed.

(4) Improve the anisotropy of the product.

We found that there are 4 points.

These Uchida have already been discussed in JP-A-55-70404, and (2) has already been discussed in JP-A-51-77.
This is discussed in Japanese Patent Application Laid-open No. 523 and Japanese Unexamined Patent Publication No. 55-10772. Regarding (3) and (4), little is known so far. Also (1),
Regarding (2), there are various new ideas, and it is desired to solve them comprehensively. In the hot-rolled sheet annealing process, high temperatures are required for annealing softening and solid dissolution of carbides, which consumes a considerable amount of energy, and in many cases, the HAP line speed is also annealing rate-limiting.

Therefore, if the hot-rolled plate annealing process can be omitted, the benefits in terms of energy saving and productivity improvement are considered to be extremely large. In this way, the present inventors specifically aimed to omit the hot-rolled plate annealing process from the manufacturing process of austenitic stainless steel thin sheets mainly made of SUS3O4, and to develop a process for manufacturing stainless steel thin sheets with excellent quality characteristics. The present invention was achieved as a result of comprehensive research aimed at developing a new process that can completely replace the above four functions. In particular, there has been little research on the problem of anisotropy in austenitic stainless copper thin sheets when hot-rolled sheet annealing is omitted, and this point was investigated in detail. Stainless steel thin plates that do not undergo hot-rolled plate annealing have a larger anisotropy at the product stage than those that undergo hot-rolled plate annealing.

If the anisotropy is large, the properties will be different in the rolling direction, in the direction perpendicular to the rolling direction, and in the rolling direction and the 45-press direction. For example, when cylindrical deep drawing is performed, selvage will be large and the product yield will be reduced.
This phenomenon is known as earring and is expressed as the earring rate. (Figure 1) In the present invention, the earrings were evaluated by a cylindrical deep drawing test, and the test conditions were 0.7
The blank diameter was 807 mφ using a TIr1n thin plate, and the punch diameter was 40 W$tφ. Our research revealed that these earrings occur due to the development of a unique texture in stainless steel sheets. Therefore, if hot-rolled sheet annealing is omitted and the development of this unique texture can be suppressed, earrings are unlikely to occur. According to experimental results, the earring ratio when hot-rolled sheets are annealed is 4 to 6%, but when hot-rolled sheets are omitted, it is 10! % earrings occurred. The inventors of the present invention have studied not only various austenitic stainless steels but also numerous component systems based on the above-mentioned concept, and have found that even if hot-rolled sheet annealing is omitted, the anisotropy is small, and therefore the earring ratio is 63%. (Average earring ratio obtained when normal hot-rolled sheet annealing) As a result of examining manufacturing processes that would result in the following, it became clear that the cold rolling process is important as a process that controls the earring ratio. .

That is, in austenitic T stainless steels of various compositions, the thickness of the hot-rolled sheets was changed, and the hot-rolled sheets were annealed (1100°C).
×10 minutes WQ) 0.7? Cold rolled once to thickness, 1100°C x 1 minute W. The final annealing of Q was performed, and the influence of the cold reduction rate was investigated. The cold rolling reduction ratio studied was 45% to 90%. The results of examining the cold rolling reduction ratio with respect to the anisotropy of austenitic stainless steel thin sheets are shown in Figure 2 (A,
8, C means the following).

8: Normal 18Cr-8Ni; No hot rolled plate annealing × [Ni
] = 18Cr-8Ni whose composition was regulated to 45.5%; no hot rolled sheet annealing) × [Ni] = 18Cr-8Ni whose composition was regulated to 41.0%; typical 18Cr without hot rolled sheet annealing
-8Ni stainless steel (a). 07C-18.4Cr-
8.7Ni-0.03P-0.04N), the hot-rolled sheet annealing was omitted and the influence of the cold rolling reduction ratio in one cold rolling was investigated, which is shown in A in the figure.

It can be seen that the earring ratio is improved as the cold rolling reduction is lower, from around 80% to 60% and 50%. The results in Figures 8 and 0 show the influence of alloy composition when hot-rolled sheet annealing is omitted. In this case as well, the earring ratio decreases as the cold rolling reduction decreases, indicating that the effect of the cold rolling reduction is large. Furthermore, it can be seen that the effects of cold rolling reduction and alloy composition act additively. That is (A)
, 8, 0, the earring ratio decreases as the regulation of the alloy composition becomes stronger and as the cold rolling reduction ratio decreases. If hot-rolled sheet annealing is omitted in the manufacturing method of austenitic stainless steel, the anisotropy of the product sheet deteriorates and the earring characteristics deteriorate, but the alloy composition has a large influence on the earring characteristics.

It was found that the main components controlling the earring rate were Ni, C, P, N, etc. Figure 3 shows the influence of Ni. When NilO% is reduced to 6%, the earring rate is greatly improved. Figure 4 shows CI:. It shows the influence of P. C improves the earring rate as it decreases from 0.08% to 0.01%, and P improves from 0.045% to 0.00.
If it decreases to 5%, the earring rate will be greatly improved. In addition, N is also preferably lower, but S has no effect at all. As a result, it was found that the above-mentioned main components exert an additive effect on reducing anisotropy.

(Figure 4) The effect of these component elements is quantitatively analyzed and the relationship with the earring rate is determined and displayed.

The component elements here are numerical values expressed in weight percent. Furthermore, this formula holds true for the following component ranges.

Thus, the alloy composition has a great influence on the earring rate,
Furthermore, it can be seen that the cold rolling reduction ratio has a large additive effect on the earrings, but as a result of quantitative analysis of the relationship between them, when the cold rolling reduction ratio of one cold rolling is expressed as x percentage,
The following relationship holds true with the earring rate He (%).

Here, the range of the component elements is as described above, expressed in weight percent, and the cold rolling reduction X is 45% to 90%. In this way, we were able to quantitatively demonstrate for the first time the effects of component elements and cold rolling reduction on the reduction of earrings in austenitic stainless steel products when hot-rolled sheet annealing is omitted.

(2) In order to obtain an earring ratio of 6% or less, which is the same as with hot-rolled sheet annealing, even if hot-rolled sheet annealing is omitted by using 2, the following relationship between alloy composition and cold rolling reduction ratio must be established. It is essential that regulations be implemented to meet the requirements.

As can be seen from this equation, if the alloy composition is restricted to low C1, low P1, low Ni, etc., a large cold rolling reduction, for example about 80%, can be obtained. Conversely, if the cold rolling reduction is as low as about 6.5%, regulation of the ingredients is not so necessary.
In order to produce thin austenitic stainless steel sheets with a low cold rolling reduction of 80% or less, a hot coil with a thickness of 2.5wt or less, preferably about 2.0Tfn, is required, but with the recent strong This became possible for the first time with the advent of hot strip mills equipped with shape control functions.

The basis for limiting the requirements of the present invention will be described below.

The earring properties of thin austenitic stainless steel sheets without hot-rolled sheet annealing are extremely influenced by the cold rolling reduction and the constituent elements of the steel.

These two effects act additively with each other, and by combining regulation of steel components and reduction of cold rolling reduction, an austenitic stainless steel thin plate with small anisotropy can be obtained.
As for the cold rolling reduction ratio, it is desirable to have a smaller one, but in combination with regulations on steel composition, the upper limit of the permissible limit can be found from the following equation.

x is the cooling rate %. The smaller the cold rolling reduction ratio, the better the anisotropy is, but in relation to the manufacturable thickness of the hot rolled coil and the thickness of the product thin plate for drawing, a cold rolling reduction ratio of less than 45% has little practical value.

Therefore, the cold reduction rate was set to 45% or more. Furthermore, the austenitic stainless steel components also affect the anisotropy in the process of omitting hot-rolled sheet annealing.

C is desirably 0.070% or less, and desirably as low as possible from an industrial and economical point of view. Like C, P is desirably 0.040% or less with respect to anisotropy, and is desirably as low as possible from an industrial and economic point of view. Ni has a large effect on the anisotropy of austenitic stainless steel thin sheets without hot-rolled plate annealing, and exhibits excellent properties at 9.5% or less, and although a lower content is preferable, the effect is saturated at 6%. .

Similar to C and P, N is preferably as low as 0 for anisotropy.
．． A content of 2% or less is highly effective and is preferably as low as possible from an industrial and economic perspective. Cr does not have a large effect on anisotropy, but for an austenitic stainless steel sheet that maintains excellent corrosion resistance and workability, it needs to have a content of 16.0% or more, and is stable in relation to the Ni content. In order to maintain the austenite phase, the upper limit is 19.0%.

The above-mentioned C, P, Ni, and N have additive effects on improving the earring properties of austenitic stainless steel thin sheets without hot-rolled sheet annealing, and they also have the effect of lowering the cold rolling reduction and the above-mentioned components. Regulatory effects act additively.

If the cold rolling reduction ratio can be reduced, a thin plate with small anisotropy can be obtained even if the composition restrictions are relaxed. Thus, from the quantitative relationship between the effect of cold rolling reduction and the effect of component elements, the earring ratio should be 6% or less; as already stated, it is necessary to satisfy the following equation.

x is the cold rolling reduction expressed as a percentage. By regulating the cold rolling reduction and the main components as described above, it is possible to produce an austenitic stainless steel thin plate with small anisotropy.

It should be noted that with regard to the content of Il as an austenitic stainless steel, a normal level of content does not have a significant effect on orthotropy.

Examples of the present invention will be described below.

18-8 stainless steels meeting the SUS3O4 standard as shown in Table 1 were melted by electric furnace-AOD method J1 or converter-furnace VOD method to obtain CC slabs with a thickness of 1607 m.

After that, it was heated in a heating furnace at 1250°C and then hot rolled as usual.
Twt thickness and 2.5? I got a thick hot coil. then 1
A sample 7 which had been subjected to a hot rolled plate annealing process at 100°C was prepared and subjected to cold rolling after shot blasting and pickling. The cold rolling was carried out once using a Sendzimir mill with a rolling roughness of 0.4 to 1.
A product plate with a thickness of 3T1$L was obtained through a normal final annealing process. Table 1 shows regulations based on component content and cold rolling reduction.
Although He (%) is expressed, in the method of the present invention shown in Table 1, He (%) is all 6.0% or less due to the effects of the ingredients and cold rolling reduction. In contrast, the comparative method has a rate of 6.0% or more. Table 2 shows the results of actually measuring the anisotropy of these products in terms of earring ratio. As a result, it was confirmed that if the method of the present invention is used, an earring ratio of 6.0% or less can be obtained even if hot-rolled sheet annealing is omitted.

[Brief explanation of the drawing]

Figure 1 shows the earring rate (He = Kawatan Futichi Chikari 00hma
x + Hmin (%)), Figure 2 is a diagram showing the influence of cold reduction rate and component elements on the anisotropy of austenitic stainless thin steel sheet, and Figure 3 is a diagram showing the influence of 18Cr-Ni stainless steel sheet (base composition 0). .04C+1&1Cr-Ni
) Earring ratio and N in the process of omitting hot rolled sheet annealing
FIG. 4 is a diagram showing the influence of the earring ratio and CP% in the process of omitting hot-rolled plate annealing of 18Cr-8Ni stainless thin steel sheet (base composition 1 & 1Cr-Ni).

Claims (1)

[Claims] 1. C 0.070% or less, Si 1.0 in weight percent
% or less, Mn 3.0% or less, P 0.040% or less, S0
．． 030% or less, Cr16.0% to 19.0%, Ni
In austenitic stainless steel containing 6.0 to 9.5% and 0.2% or less of N, the steel of the composition is cast, hot rolled, descaled, and the cold rolling reduction is 45% or more and the component elements are A method for manufacturing austenitic stainless steel sheets and steel strips, which comprises performing cold rolling regulated by the following formula determined in relation to the above, and then final annealing. 0.25×[x]+102×[C]+90×[P]+6
4 x [N] + 4 x [Ni]≦62.8% [x]: Cold rolling reduction percentage [C]: [P]...other Weight percent of each element