JPS5818436B2 - Manufacturing method for cold-rolled stainless steel thin steel sheets or steel strips with excellent buffing properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention deals with fine dot-like or linear defects (puff polishing defects) that occur when the surface of a product is polished with fine abrasive-attached cloth or paper (commonly known as puff). The present invention relates to a method for manufacturing cold-rolled thin steel sheets or copper strips made of L7 stainless steel with the aim of reducing

Generally, for stainless steel cold-rolled thin steel sheets or steel strips,
After the final manufacturing process or processing by the user, puff polishing is often applied to improve the surface roughness and finish it to a mirror finish.

When this puff polishing process is performed, minute dot-like or linear defects (referred to as puff polishing defects) are exposed on the product surface, and they may remain on the product surface without being completely removed by this puff polishing. , such puff polishing defects greatly impair the uniformity of the product.

Particularly when the beauty of the surface is emphasized, this puff polishing defect becomes a fatal defect and significantly reduces the value of the product, regardless of the quality of other properties.

For example, in the production routing of conventional cold-rolled stainless steel sheets or strips as shown in FIG. 1, the degree of puff abrasion defects in the products varies greatly.

For this reason, for products in which puff polishing defects are a particular problem, conventional methods include removing the surface layer of the strip by belt grinding during the cold rolling process as shown in Figure 2, or removing the surface layer of the strip by belt grinding as shown in Figure 3. Passing through the cold rolling line and the subsequent annealing and pickling line two or more times (commonly known as the intermediate rolling course)
methods may be adopted.

According to the conventional method shown in FIG. 2 or 3, it is possible to improve puff polishing defects and reduce the variation in the degree of puff polishing defects in products compared to the method shown in FIG. 1.

However, these conventional methods additionally require a belt grinding line, a cold rolling line, and an annealing pickling line, and the cost required for this is very large, resulting in an increase in manufacturing costs. .

The present invention provides a method for easily and effectively reducing puff polishing defects without requiring additional steps as in the conventional method. After repeatedly applying bending strain to the strip or the lip of the hot-rolled strip 1 after annealing using a broker or a leveler, nitric acid (e.g. 3 to 10% by weight) is applied to the lip.
) and hydrofluoric acid (e.g., 2 to 5% by weight) in a mixed aqueous solution, followed by cold rolling on a regular cold rolling line. Stainless steel with excellent puff polishability. It is in the manufacturing method of cold-rolled thin steel sheets.

In other words, as a result of repeated investigation into the causes of puff polishing defects as described above, the present inventors have found that the cause lies in the descaling process of the hot rolled strip in the conventional manufacturing process. By improving this descaling process, they succeeded in significantly reducing the occurrence of puff polishing defects.

Generally, the scale that occurs in stainless steel is -・
Mechanical descaling, such as steel shot or Normally, chemical pickling was carried out by shot blasting with scale grids, etc., but when descaling was performed by projecting steel shot or steel crystals using such a mechanical descaling device, (S)
l) The surface layer of the pump changes, which is one of the causes of puff polishing defects.
3 Therefore, unless this surface layer is removed or improved, the degree of puff polishing defects cannot be reduced, and conventional treatments such as the process examples shown in Figures 2 and 3 cannot reduce the degree of puff polishing defects. This cannot be the basic solution.

Based on this knowledge, the present invention adopts a descaling method that replaces mechanical descaling by repeatedly applying bending to the strip using a processor or an I/veler, followed by chemical pickling treatment to achieve the required descaling. While achieving descaling of It is.

The method of the present invention will be specifically explained below using Examples.

Example 1 A 2B finished product of 5US304 steel having the chemical composition shown in Table 1 was manufactured using the following manufacturing route.

The following puff polishing defect test was conducted on the surface of the obtained product.

That is, as shown in Table 2, +1.000, +400,
≠240, ≠150, ≠80 abrasive paper is pressed against the product surface with a pressure of 3 kg/J, and the same surface is polished at a speed of about 1 m for 3 to 5 seconds, and a new one is removed every 25 times. After polishing the polishing paper for 50 minutes, the polished surface was
The samples were observed under a microscope at a magnification of ~100 times, and the presence or absence of remaining defects was evaluated according to the evaluation procedure shown in Table 2.

The results of this puff polishing defect test are shown in Table 3.

For comparison, Table 3 shows buffing defect tests of products manufactured by the same manufacturing process as in this example, except that conventional steel shot projection was performed instead of the leveler braking in this example. The results of seven experiments are also shown as a comparative example.

As is clear from the results in Table 3, when using the method of the present invention,
There was little variation in the degree of occurrence of puff polishing defects on 2B-finished austenitic stainless steel products, and good results were obtained in all cases, exceeding the puff polishing defect determination CB).

Example 2 A BA finished product of SUS 304 steel having the chemical composition shown in Table 4 was manufactured by the following manufacturing route.

Manufacturing routing hot rolled strip (3,8rrvn, ) ↓ Continuous annealing ↓ Scale breaking by leveler ↓ Chemical pickling (HN033~10%, HI”2~5%, ↓
Liquid temperature: 50-60°C) Finish rolling (3,8→2°O cylinder) ↓ Finish annealing (continuous bright annealing) ↓ The surface of the product obtained by skin pass rolling was subjected to the C-puff polishing defect test in the same manner as in Example 1. The results shown in Table 5 were obtained.

For comparison, Table 5 shows the results of a puff abrasive defect test of a product manufactured by the same manufacturing route as in this example, except that conventional steel shot projection was performed instead of braking by the leveler in this example. The results are also shown as comparative examples.

As is clear from the results in Table 5, when using the method of the present invention,
There was little variation in the degree of occurrence of pub polishing defects in 2B finished products made of austenitic stainless steel, and good results were obtained in all cases, exceeding the puff polishing defect determination (CB).

Example 3 A 2B finished product of 430 steel having the chemical composition shown in Table 6 was manufactured using the following manufacturing route.

Production routing hot rolled strip (3,6M) ↓ Bell-shaped annealing ↓ Scale breaking by leveler ↓ Chemical pickling (HN033~10%, HF2~5%, ↓
Liquid temperature: 50-60°C) Finish rolling (36→1.5 mm) ↓ Finish annealing and pickling (continuous annealing and pickling) ↓ Puff polishing defects similar to those in Example 1 were observed on the product surface obtained by skin pass rolling. The test was conducted and the results shown in Table 7 were obtained.

For comparison, Table 7 shows the results of pub polishing defect tests of products manufactured by the same manufacturing route as in this example, except that conventional steel shot projection was performed instead of braking by the leveler in this example. The results are also shown as comparative examples.

As is clear from the results in Table 7, when using the method of the present invention,
There was little variation in the degree of occurrence of puff polishing defects in 2B finished products of ferritic stainless steel, and good results were obtained in all cases, exceeding the puff polishing defect determination CB).

[Brief explanation of the drawing]

FIG. 1, FIG. 2, and FIG. 3 show an example of a manufacturing process for a cold-rolled stainless steel thin steel plate or steel strip by a conventional method.

Claims (1)

[Claims] 1 After repeatedly applying bending strain to a stainless steel hot-rolled strip or an annealed hot-rolled strip using a processor or a leveler, chemical pickling treatment is performed using a pickling solution containing nitric acid and hydrofluoric acid, followed by normal cooling. A method for producing cold-rolled stainless steel thin steel sheets or copper strips with excellent puff abrasiveness, which comprises cold rolling on an inter-rolling line.