JPH06241B2 - Hot rolling method for stainless steel - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hot rolling method for stainless steel, and more particularly to a method for preventing surface flaws generated at the side edges of a material to be rolled.

<Prior Art> In recent years, the demands of consumers for the surface properties of stainless steel sheets have become more and more strict. In addition, the width accuracy of the rolled steel sheet has been improved, and the surface flaw on the side end of the rolled material has been highlighted as a very serious problem. In particular, no effective preventive measure is found for the linear flaws (hereinafter, referred to as edge seams) 3 that are seen on the front and back surfaces near the side end portions 2 of the material 1 to be rolled as shown in FIG. It is generally known that a cause of the edge seam 3 is that a flaw generated at a side end portion of a material to be rolled in a rough rolling step wraps around and remains on the front and back surfaces due to width expansion during horizontal rolling.

Conventional methods for preventing such edge seams include, for example, Japanese Patent Publication No. 50-14632 and Japanese Patent Laid-Open No. 56-6.
Methods disclosed in Japanese Patent Laid-Open No. 707, JP-A-53-28542 and the like are known.

As shown in FIG. 2, the technique of Japanese Patent Publication No. 50-14632 is applied to a material 1 to be rolled by an edger roll 4 with a convex caliber.
In addition, the technique of JP-A-56-6707 gives a training effect to the side surface of the rolled material by significantly reducing the material to be rolled. Is also intended to prevent cracks occurring on the side surface of the material to be rolled by the training effect.

On the other hand, the technique disclosed in Japanese Patent Laid-Open No. 53-28542 is to prevent the edge seam by applying a reduction to the ridge portion 7 of the material 1 to be rolled by the brim portion 6 of the edger roll 5 with caliber as shown in FIG. Therefore, it is intended to smooth the flaw generated at the side end portion 2 of the rolled material 1 at the ridge portion 7 of the rolled material.

<Problems to be solved by the invention> However, the cause of the edge seam that occurs when hot rolling ferritic, austenitic and martensitic stainless steel occurs on the side surface of the conventionally known material to be rolled described above. It has been found that the cracks are not cracks that occur, but irregularities (hereinafter referred to as wrinkles) caused by the anisotropy of the crystal grains in the side surface layer portion.

By the way, when applying the technique of Japanese Patent Publication No. 50-14632 or Japanese Patent Laid-Open No. 56-6707 in hot rolling stainless steel, that is, the side surface layer portion is utilized by utilizing the forging effect by the width reduction of the material to be rolled. In order to reduce the size of the crystal grains and prevent the generation of wrinkles, a very large width reduction amount is required, which is uneconomical because the edger mill's capacity becomes very large, and when a large reduction is applied. However, there is a problem that the material to be rolled is likely to buckle, which is not an effective means for preventing edge seams.

Further, when the ridge portion of the material to be rolled is pressed down by using the method of the above-mentioned Japanese Patent Laid-Open No. 53-28542, wrinkle collapse is promoted to easily cause a barbed edge seam, and therefore an effective method for preventing edge seam is I won't. Further, when the edger roll with a caliber is used, there is a drawback that it is not general-purpose because the size of the strip to be rolled is limited.

The present invention has been made in view of the above circumstances, and provides a method suitable for preventing a surface flaw generated at a side end portion of a material to be rolled even in hot rolling of stainless steel. With the goal.

<Means for Solving Problems> The present inventors have made earnest studies on surface flaw prevention during hot rolling of ferritic, austenitic and martensitic stainless steels, and as a result, the width reduction pass by the edger mill The present invention has been completed based on the finding that there is a limit in the magnitude of the horizontal reduction rate in the above and that there is also a limitation in the width reduction amount in the width.

The present invention, when hot-rolling stainless steel, in a rough rolling step in which horizontal rolling passes and width rolling passes are combined multiple times, the total rolling reduction of horizontal rolling passes performed between the width rolling passes is 50% or less. And a single width reduction amount of the width rolling pass is set to 40 to 150% with respect to the plate width difference in the thickness direction of the rolled material after the horizontal rolling pass. Is.

<Operation> A hot rolling experiment was conducted on ferritic, austenitic and martensitic stainless steels using a reversible rough rolling mill consisting of an edger mill and horizontal rolling rolls and a tandem finishing rolling mill. found.

If the total reduction rate r _t of the horizontal rolling path between the width rolling passes according Ejjamiru exceeds 50%, wrinkles occurring at the side end portion of the material to be rolled, can not be smoothed by width rolling pass by Ejjamiru.

Here, if the total of the reduction ratios in the horizontal rolling pass is small, the wrinkles on the side surface of the rolled material are shallow and small, so that the smoothing of the wrinkles by the width rolling pass becomes easy.Therefore, the lower limit thereof needs to be particularly limited. Not be.

If the width reduction Δw in one time in the edger mill is less than 40% of the plate width difference ΔB (hereinafter referred to as the bulging amount) in the thickness direction of the end portion of the material to be rolled after the horizontal rolling pass, the edger mill reduces the width. Since the pressing force on the side surface of the rolled material becomes weak, it is not possible to sufficiently smooth the wrinkles occurring at the ridge 7 (see FIG. 3).

In addition, as shown in FIG. 4, the amount of bulging ΔB is set such that the plate width on the surface of the material 1 to be rolled is W _1, and both end portions 2,
If the plate width at the maximum bulge position at ₂ is W ₂ , ΔB
= Expressed as _W 2 -W _1.

Further, the Δw is 150 with respect to the bulging amount ΔB.
If it is larger than%, a large dog bone is formed and large deep wrinkles or folds are likely to occur on the ridge of the rolled material.

Therefore, during hot rolling of ferritic, austenitic and martensitic stainless steels, if the conditions of horizontal reduction and width reduction in the rough rolling step are controlled within the above range, the material to be rolled is It is possible to prevent wrinkles from occurring at the ends.

<Examples> Examples of the present invention will be specifically described below.

As a test material, using a slab of five ferritic stainless steels (SUS430) with a plate thickness of 180 mm and a plate width of 937 mm, and two austenitic stainless steels (SUS304) and martensitic stainless steels (SUS410), in a heating furnace. After heating to 1250 ° C., the plate thickness 27 was applied in the rough rolling process according to the pass schedule shown in Table 1.
A sheet bar having a thickness of 3.5 mm was prepared, and then a product having a plate thickness of 3.5 mm was finished by a 6-stand tandem rolling in a finish rolling process.
The width reduction by the edger mill in rough rolling was performed on the entry side of each odd numbered pass.

At this time, the total reduction ratio r _t (%) of the horizontal rolling passes between the width rolling passes in the rough rolling process, the width reduction amount Δw (mm) once in the edger mill, and the bulging of the side end to be rolled after the horizontal rolling pass. Ratio of amount ΔB (mm), that is, (Δw / Δ
B) × 100 (%), and as shown in FIG. 1, together with the distance dmax (mm) from the side end 2 of the edge seam 3 located at the center in the width direction of the material to be rolled after the horizontal rolling pass. The results are shown in Table 2.

As can be seen from Table 2, in the conventional example, the total reduction ratio r _t of the horizontal rolling pass between the third and fourth width rolling passes by the edger mill exceeds 50%. And the dmax of 17.3 mm, the dmax of the experimental materials I, V and VI satisfying all the conditions of the present invention was 2.0 mm or less, and the yield was 99.5% or more. Was improved.

Here, the yield is obtained by the following equation, where W is the plate width of the material to be rolled.

Note that the experimental material II is the width reduction Δ of the third pass by the edger.
When w is less than the condition of the present invention and when the experimental material III is conversely large, the dmax of these is 8 to 10 mm, which is an improvement as compared with the conventional example, but the yield is 98%.
The following is still a problem.

Although experimental material IV is obtained by a three-pass width reduction by edger, it exceeded 50% of the total reduction ratio r _t of the horizontal pressure between the first pass and the second pass of the width reduction, dmax Has also deteriorated to 22 mm.

In carrying out the present invention, the bulging amount ΔB was predicted by the following method and used for setting the width reduction amount Δw. That is, first, the width spread amount ΔB ^* of the material to be rolled by the horizontal rolling pass between the width rolling passes of the edger mill is calculated by the previous width reduction amount Δw ^* and the plate thickness ratio Hi / H before and after the horizontal rolling pass.
o, empirical formulas as functions of roll diameter to plate thickness ratio D / Hi, plate thickness to plate width ratio Hi / Bi, plate width to contact arc length ratio B / ld, and friction coefficient μ did. Also, the shape factor C
An empirical formula was created in which ^* is a function of Hi / Ho, Hi / Bi, D / Hi and μ described above. And B = ΔB ^*
An empirical formula of × C ^* was created to accurately predict the bulging amount ΔB.

<Effects of the Invention> As described above, according to the present invention, it is possible to suppress surface defects that occur during hot rolling of stainless steel, which contributes to an improvement in product yield.

[Brief description of drawings]

FIG. 1 is a partial perspective view illustrating an outline of an edge seam,
2 and 3 are partial front views showing a conventional example of edge seam prevention, and FIG. 4 is a front view illustrating the amount of bulging at the end of the material to be rolled after a horizontal rolling pass in rough rolling. 1 ... Rolled material (stainless steel), 2 ... Side end, 3 ... Edge seam.

Claims (1)

[Claims] 1. A total rolling reduction of 50% of horizontal rolling passes between width rolling passes in a rough rolling process in which horizontal rolling passes and width rolling passes are combined a plurality of times during hot rolling of stainless steel. The hot rolling of stainless steel is as follows, and the width reduction amount of one time of the width rolling pass is 40 to 150% with respect to the plate width difference in the thickness direction of the rolled material after the horizontal rolling pass. Method.