JPH07310145A - Stainless hot rolled steel sheet for working and its production - Google Patents

Abstract

PURPOSE:To produce a stainless hot rolled steel sheet having a black film on the surface and excellent in workability by subjecting a stainless slab to hot rough rolling, removing surface scales and thereafter executing finish rolling under specified temp. conditions. CONSTITUTION:At the time of producing a hot rolled steel sheet by heating stainless steel of every kind, e.g. to 1150 to 1300 deg.C and executing hot rough rolling and finish rolling, it is subjected to hot rough rolling to form into a sheet bar, and after that, surface scales formed at the time of the hot rough rolling are removed away by the spraying of pressurizing water of >=150kg/cm<2>. Immediately after that, it is passed through a finish rolling mill to form into a hot rolled sheet having a final objective sheet thickness. At this time, by controlling the inlet side temp. of the hot rolled sheet in the finish rolling mill to 970 to 1000 deg.C and the outlet side temp. to 890 to 930 deg.C, a black film having 4 to 9mum thickness per side is formed on the surface of the stainless steel discharged from the finish rolling mill. Its workability is made good, furthermore, the surface of the stainless steel sheet is not flawed in the process of handling owing to the presence of the black film, and after the working, the black film can easily be removed away by direct grinding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-rolled stainless steel sheet for working and a method for producing the same, and in particular, in addition to improving the workability such as press formability, it prevents the occurrence of flaws during handling and improves the grindability thereafter. It is intended to make various improvements.

[0002]

2. Description of the Related Art Generally, so-called black-skin stainless hot-rolled steel sheet (including steel strip; the same applies hereinafter) having a surface scale called black skin is mainly used for presses such as motorcycle disc brakes and Western tableware. It is used for the purpose of performing heat treatment before and after surface grinding (polishing) and sometimes before and after molding into a desired product shape by processing such as. Here, the black scale is necessary to prevent flaws on the product surface during processing such as pressing and handling,
When the processing is completed, this black skin must be removed by grinding, polishing, pickling, etc. However, since the black skin usually has a thickness of 12 to 15 μm and is not easily removed, it is the actual situation that the black skin is descaled by shot blasting and then ground and polished.

By the way, conventionally, in the production of hot-rolled stainless steel sheets, stainless steel slabs soaked at 1150 ° C to 1300 ° C in a heating furnace are removed by a scale breaker from the primary scale generated in the heating furnace before rough rolling. After that, it is processed by reducing the thickness of the sheet bar with a rough rolling machine, then rapidly rolling it to a predetermined dimension with a finishing rolling machine, controlling the winding temperature if necessary, and winding it with a coiler. It was

As described above, during hot rolling of stainless steel, there is concern about precipitation of a χ phase, a σ phase, or a phase causing brittleness at 475 ° C. Although the temperature and the like were controlled, most of the stainless steels did not control the surface black scale. Further, conventionally, neither the inlet side nor the outlet side temperature of the finish rolling mill is specified,
Furthermore, descaling of the sheet bar on the entry side of the finishing mill is not performed. The reason for this was that there was concern that the sheet bar temperature would decrease due to descaling and the roll surface of the finish rolling mill would be damaged, and that the black scale on the steel sheet surface would be affected by pickling following annealing after hot rolling. This is probably because it was based on the general recognition that it could be easily removed.

However, in the field where the scale is used with a black scale, the thickness thereof is thicker than necessary, so that not only the working environment is deteriorated by dust generated during processing, but also the life of the mold is shortened, and further, the above-mentioned. As described above, there was a disadvantage that a great amount of labor was required for the subsequent removal of the black scale.

[0006] As a technique which refers to the surface scale of stainless steel, Japanese Patent Laid-Open Nos. Sho 60-170503 and Sho 60 are known.
-174201 and JP-A-60-174202, there are hot rolling methods for stainless steel. The above-mentioned technique, on the metal surface of the material to be rolled exposed during hot rolling, blows air, oxygen gas, steam, etc., or regenerates an oxide scale by air cooling or heating, and then rolls the next pass. By doing so, the occurrence of surface defects in the hot rolling process is prevented. However, none of the above techniques mentions the thickness of the regenerated oxide scale and the difficulty of its removal.

[0007]

As described above, no technique has been proposed so far for facilitating the removal of the black scale while maintaining the effectiveness of the black scale, and its development has not been proposed. Was wanted. The present invention advantageously responds to the above-mentioned requirements, and by controlling the thickness of the black scale produced during hot rolling, not only the workability such as press formability is improved but also defects during processing / handling. It is an object of the present invention to propose a hot-rolled stainless steel sheet for processing, which effectively prevents the occurrence of cracking and deterioration of the working environment and further significantly improves the subsequent grindability together with its advantageous manufacturing method.

[0008]

That is, the present invention is a stainless hot-rolled steel sheet for working, characterized in that it has a black skin scale having a thickness of 4-9 μm per surface on one surface.

Further, according to the present invention, after heating a slab for stainless steel, rough rolling and then finish rolling to produce a hot-rolled stainless steel sheet, 150 kg / cm ² or more is applied to the sheet bar after the rough rolling. Of hot-rolled stainless steel sheet for processing, which is characterized by performing descaling treatment with the water pressure of and controlling the inlet side temperature and outlet side temperature of the finishing rolling mill in the ranges of 970 to 1000 ° C and 890 to 930 ° C, respectively. Is the way.

The composition of the stainless steel to which the present invention is applied is not particularly limited, and any conventionally known stainless steel is suitable. The particularly preferable steel types are as follows. (1) Austenitic stainless steel ・ SUS304 C ≦ 0.08wt%, Si ≦ 1.00wt%, Mn ≦ 2.00wt%, P ≦ 0.045
wt%, S ≦ 0.030 wt%, Ni: 8.00 to 10.50 wt%, Cr: 1
8.00 to 20.00 wt% ・ SUS316L C ≦ 0.03 wt%, Si ≦ 1.00 wt%, Mn ≦ 2.00 wt%, P ≦ 0.045
wt%, S ≦ 0.030 wt%, Ni: 12.00 to 15.00 wt%, Cr:
16.00 to 18.00 wt% Mo: 2.00 to 3.00 wt% (2) Ferritic stainless steel ・ SUS430 C ≦ 0.12 wt%, Si ≦ 0.75 wt%, Mn ≦ 1.00 wt%, P ≦ 0.040
wt%, S ≦ 0.030 wt%, Cr: 16.00 to 18.00 wt%, Ni ≦
0.60wt% ・ SUS444 C ≦ 0.025wt%, Si ≦ 1.00wt%, Mn ≦ 1.00wt%, P ≦ 0.0
40 wt%, S ≦ 0.030 wt%, Cr: 17.00 to 20.00 wt%, M
o: 1.75 to 2.50 wt%, Ni ≦ 0.60 wt%, Nb ≦ 0.80 wt%, Nb /
C + N ≧ 8 (3) Austenitic / ferritic stainless steel SUS329J ₁ C ≦ 0.08wt%, Si ≦ 1.00wt%, Mn ≦ 1.50wt%, P ≦ 0.040
wt%, S ≦ 0.030 wt%, Ni: 3.00 to 6.00 wt%, Cr: 23.0
0 to 28.00 wt%, Mo: 1.00 to 3.00 wt% (4) Martensitic stainless steel ・ SUS410 C ≦ 0.15 wt%, Si ≦ 1.00 wt%, Mn ≦ 1.00 wt%, P ≦ 0.040
wt%, S ≦ 0.030 wt%, Cr: 11.50 to 13.50 wt% ・ SUS420J ₁ C: 0.16 to 0.25 wt%, Si ≦ 1.00 wt%, Mn ≦ 1.00 wt%, P
≤0.040 wt%, S≤0.030 wt%, Cr: 12.00 ~ 14.00 wt
% (5) Others ・ R410DB C ≦ 0.090 wt%, Si ≦ 0.50 wt%, Mn ≦ 1.00 to 2.50 wt%,
P ≦ 0.040 wt%, S ≦ 0.030 wt%, Cr: 10.00 to 14.50 w
t%, Ni ≦ 0.60wt%, C + N: 0.0400 to 0.1000

Below, the experimental results that have led to the completion of the present invention will be explained. Thickness: 195 mm R410DB steel slab is heated to 1230 ℃, then subjected to descaling with a water pressure of 150 kg / cm ² or more to the sheet bar at 1020 ℃, which was reduced to 30 mm by rough rolling, and then finished. The temperature on the inlet side and the temperature on the outlet side of the rolling mill were variously changed to generate black scales having various thicknesses on the surface. Fig. 1 shows the results of an investigation of the occurrence of flaws and the degree of difficulty of polishing during pressing or handling of the obtained hot-rolled stainless steel sheet with a black scale in relation to the thickness of the black scale per side. .

As is clear from the figure, if the thickness of the black scale is less than 4 μm per side, the material will be flawed during processing such as pressing or handling, while if it exceeds 9 μm, the black scale will be removed after processing. In that case, pretreatment such as shot blasting is required. On the other hand, if the thickness of the black scale is controlled within the range of 4 to 9 μm per side, no flaws occur during processing such as pressing or handling, and direct polishing without the need for pretreatment such as shot blasting. In addition, the life of the mold and the working environment can be improved.

Next, the manufacturing method of the present invention will be described. First, the slab manufacturing method may be either an ordinary continuous casting method or an ingot making method. Slab heating temperature is 11
A temperature of 50 to 1300 ° C is suitable. Then, rough rolling and finish rolling to give a hot rolled steel sheet, in the present invention, during this hot rolling step, particularly after rough rolling is subjected to a descaling treatment to remove excess black scale of the surface, It is important to control the inlet temperature and the outlet temperature of the finish rolling mill to generate a black scale of a predetermined thickness on the surface. In Figure 2, SUS420J ₁ with a thickness of 195 mm
After heating the steel slab to 1250 ° C, it is rough rolled into a 27 mm sheet bar, then subjected to descaling with a water pressure of 150 kg / cm ² or more, and then finish-rolled at various inlet and outlet temperatures. The results of investigations on the relationship between the inlet and outlet temperatures of the finishing mill and the black scale scale and the occurrence of surface flaws during the test are summarized below.

As is clear from the figure, 4 to 4 per side.
In order to obtain a good black scale thickness of 9 μm, it is essential to control the inlet side temperature and the outlet side temperature of the finish rolling mill in the ranges of 970 to 1000 ° C and 890 to 930 ° C, respectively.
Even if the inlet side temperature of the finishing rolling mill exceeds 1000 ° C, the black scale does not become thinner, and not only does it cause an economic loss due to the increase in heating temperature, but it also causes surface defects due to this heating. There is a disadvantage to cause. Further, if the exit side temperature of the finish rolling mill exceeds 930 ° C, surface flaws also occur due to the increase in heating temperature. Furthermore, if the inlet temperature of the finish rolling mill falls below 970 ° C or the outlet temperature falls below 890 ° C, the water pressure of 150 kg / cm ² or more before finishing rolling, for example 400
Even if the descaling is performed with a water pressure of kg / cm ^2, the black scale is 10 μm or more, and the black scale of the proper thickness according to the present invention cannot be obtained.

Further, in the present invention, the reason why the descaling pressure after rough rolling and before finish rolling is limited to 150 kg / cm ² or more is that at lower pressures, the inlet side temperature and the outlet side temperature of the finish rolling mill are reduced. Even if the temperature is adjusted to the above-mentioned preferable range, a thin black scale of 9 μm or less cannot be obtained. It is desirable that the water pressure is higher, but the effect reaches saturation when the pressure exceeds 400 kg / cm ² , so the upper limit is preferably about 400 kg / cm ² .

[0016]

【Example】

Example 1 For five types of steel (three types for each plate thickness) shown in Table 1, various changes were made to the descaling water pressure after rough rolling and the inlet side temperature and the outlet side temperature of the finishing rolling mill to obtain various surface types. To produce a black scale of thickness. The composition of each steel type is shown in Table 2. 30mm from each obtained steel plate
20 pieces of each were pressed into a disc brake shape of a φ motorcycle, and the results of examining the presence or absence of surface flaws during processing and handling and the grindability when the pressed disks were simultaneously ground from both sides, It is also shown in Table 1. It should be noted that those with a black scale scale of 3 μm or less had flaws on the surface during the working process and were therefore all excluded from the grinding test.

[0017]

[Table 1]

[0018]

[Table 2]

As is clear from Table 1, all the steel sheets according to the present invention provided with the black scale of proper thickness have no surface flaw during processing and handling, and need to be subjected to descaling treatment such as shot blasting. It was possible to carry out the grinding directly without. Furthermore, it was also confirmed that such a steel sheet reduces dust during processing, and that the die life is significantly improved as compared with the conventional material.

Example 2 Five types of steel slabs shown in Table 2 were heated to 1230 ° C. and rough-rolled to a sheet bar thickness shown in Table 3, and various descaling pressures and finishes shown in Table 3 were also applied. Hot-rolled steel sheets were manufactured at the rolling mill inlet temperature and outlet temperature.
The results of examining the thickness of the black scale scale formed on the surface of the obtained hot rolled steel sheet are also shown in Table 3.

[0021]

[Table 3]

As is clear from the table, only when hot rolling was carried out according to the method of the present invention for all steel types,
A black scale having a suitable thickness of 4 to 9 μm is formed on each side.

Example 3 Furthermore, Table 4 shows the results of an examination of the mold life of R410DB according to the present invention and a conventional material (black skin scale thickness: 13 μm). The results in Table 4 show the die life when a 4 cm square automobile part is pressed from a hoop with a plate thickness of 5.0 mm.
It is shown by the ratio of the number of strokes in the case of the conventional material and the number of strokes of the material of the present invention.

[0024]

[Table 4]

As is clear from the table, in the case of this invention material, the mold life could be extended to three times that of the conventional material. Although only the representative stainless steel has been described in the above-described embodiments, it goes without saying that the present invention is not limited to this and can be applied to other stainless steels.

[0026]

According to the present invention, the surface has a thickness of 4 to 9 μm.
The stainless hot-rolled steel sheet with a black skin scale of m is free from flaws during processing such as pressing and handling. Further, the surface grinding and polishing treatments can be performed directly without performing the pre-descaling treatment such as shot blasting, and the process can be saved. Therefore, the economical effect thereof is great. Furthermore, the thinning of the black scale layer not only reduces dust during processing, improves the working environment, but can also be expected to dramatically improve the life of the mold. Furthermore, by utilizing the present invention in the production of ordinary white leather stainless steel, it is expected that the pickling efficiency of the black leather scale will be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a thickness of a black scale per one surface, a state of occurrence of flaws during pressing or handling, and a difficulty level of polishing.

FIG. 2 is a diagram showing the influence of the inlet side temperature and the outlet side temperature of the finish rolling mill on the thickness and surface flaws of the black scale.

Claims (2)

[Claims] 1. A hot-rolled stainless steel sheet for processing, having a black leather scale having a thickness of 4 to 9 μm per surface on one surface. 2. After heating the stainless steel slab,
When manufacturing a hot-rolled stainless steel sheet by rough rolling and then finish rolling, the sheet bar after rough rolling is subjected to descaling with a water pressure of 150 kg / cm ² or more, and the inlet temperature of the finishing rolling mill and Output temperatures of 970 to 1000 ° C and 890 respectively
A method for producing a hot-rolled stainless steel sheet for processing, which is characterized in that the temperature is controlled in the range of to 930 ° C.