JPS60194019A - Manufacture of nonoriented electrical steel sheet having superior shape and magnetism - Google Patents

Abstract

PURPOSE:To manufacture a nonoriented electrical steel sheet having a fine shape and superior magnetism by subjecting a steel having a low Si and Al content to hot rolling, self-annealing, cooling in a time represented by a specified equation, pickling and cold rolling. CONSTITUTION:A steel contg. <=2.0% Si+Al is hot rolled, self-annealed for about 10-40min, and cooled to <=600 deg.C in a time (t) represented by the equation. The cooling is carried out while retaining the grains recrystallized uniformly to a prescribed grain size without forming coarse grains. The resulting plate is pickled and cold rolled to a prescribed final thickness. The thickness of the plate is uniformly reduced during the cold rolling, and a cold rolled steel sheet having a fine shape and superior magnetism is obtd.

Description

[Detailed description of the invention] (Industrial application field) -+ fi Ellll Iam If lrL C
31 tons, yrf mut now m −ml σ) Jag
-b tk & relates to a method of manufacturing electrical steel sheets.

(Prior art) Regarding the magnetic properties of non-oriented electrical steel sheets used as materials for electrical equipment, in recent years there has been a strong worldwide demand for lower core loss and higher magnetic flux density, especially as a result of plans to improve the efficiency of electrical equipment. It's here. Therefore, in the manufacturing process, impurities in the steel components are reduced, and magnetic properties are improved by using brass, hot-rolled sheet annealing, etc. However, since increasing the processing conditions as described above would lead to an increase in costs, the present inventors first proposed an annealing method using the self-retained heat of the hot-rolled coil during hot-rolling, as described in Japanese Patent Publication No. 57-1983.
It was proposed in Japanese Patent No. 43132 and efforts have been made to improve magnetism.

However, the hot-rolled sheet self-annealing method is also particularly different, and in the case of electrical steel sheets with an At content of 2.0 or less, normal annealing conditions are used, that is, in slow cooling after self-annealing, the hot-rolled sheet is The recrystallized grains become extremely coarse, and the difference in elongation between the coarse grains and normal grains during the subsequent cold rolling causes problems such as plate thickness variation or gauge hunting in many parts, resulting in the shape after rolling being changed. There was a problem with it becoming defective.

(Objective of the Invention) The present invention is directed to producing a non-oriented electrical steel sheet from an electrical steel material with a low content range of Si and At, and to obtain a non-oriented electrical steel sheet with a good shape even after self-annealing. The purpose of this invention is to provide a manufacturing method that can be used.

(Structure of the Invention) The present invention involves hot rolling a steel containing (81+At) of 2.0 or less, and then fully self-annealing the hot-rolled plate, and after the self-annealing, 60%
A complete method for manufacturing a non-oriented electrical steel sheet with excellent shape and magnetism, characterized by cooling to 0°C or less for the time shown by the following formula (1), followed by pickling and cold rolling to obtain a product thickness. This is a summary, and the details are as follows.

The present inventors have conducted various experiments and studies on the self-annealing conditions for steel containing 2% or less of St and At, and have confirmed that there is a close relationship between the steel composition and the self-annealing conditions.

In other words, it has been found that the problem of poor shape after cold rolling can be solved by controlling the cooling time from each self-annealing temperature to 600°C or less, a temperature range in which coarse grains do not occur, to a specific time in consideration of this relationship. It is.

The cooling time t is expressed by the following equation.

t"'<(38,2X(st+Az)'+o,o4x(
Self-annealing degree)"+self-annealing time (minutes)-40) That is, the cooling time is regulated by the content of Si and At and the self-annealing conditions.

Note that components other than Si and At in the present invention are C:0.
0.02% or less, Mn: 196 or less, P: 0.2% or less, etc., may contain components of ordinary non-oriented electrical steel sheets.

The method of self-annealing hot rolled sheets in the present invention involves using a recuperator cover lined with a sufficient heat insulator without a heat source, or, for further perfection, using a heat insulating cover with a heat source to control the temperature. There is a way to achieve uniformity. According to this method, the recrystallization of the hot-rolled sheet and the improvement of the magnetic properties of the product sheet are performed uniformly, but if the cooling after recrystallization of the hot-rolled sheet is too slow, grain growth will occur in the central part of the coil where the temperature is difficult to decrease. As the process progresses, the above-mentioned coarse grains are generated locally.

Therefore, the self-annealing time is usually completed in 10 to 40 minutes, but the cooling time after that - @si, ht@, and the cooling time to 600 °C for the self-annealing temperature is expressed as the time (minutes) in the above formula.
If cooling is performed within 100 mL, coarse grains will not be generated, and the product will be cooled while being uniformly recrystallized to a predetermined size. Good magnetism can be obtained after annealing.

Also, if the coil after self-annealing is left to cool in the air,
Although thick scale remains and impairs pickling properties, the above-mentioned rapid cooling allows the scale of the hot rolled sheet to be kept thin, which significantly improves pickling properties and is effective. Therefore,
From the point of view of improving pickling properties, the method of the present invention is also effective for Taka81 material that does not generate coarse grains.The material used in the present invention may be ordinary converter melted steel, continuous casting material, or hot-rolled steel. It may also be carried out in a conventional hot rolling mill.

As for the rapid cooling method according to the present invention, any means such as cooling the coil by spraying water on the coil or immersing the coil in a water tank may be used. For the subsequent pickling, cold rolling, and annealing, commonly used pickling equipment, cold rolling mills, continuous annealing furnaces, etc. will be used. Example) A slab of S12.0% to 0.1% of the four sulfur components shown in Table 1 was hot-rolled, and the coil after rolling was placed in a heat-retaining cover equipped with a heater to prevent the inside and outside of the coil. After reheating the cooling part of the coil and recrystallizing it by self-retained heat for a total of 40 minutes at the temperature shown in Figure 1 over the entire length of the coil, the heat insulating cover was removed and the coil was heated as shown in Table 2. Figure 2 shows the particle sizes of those that were left to cool in the air as they were and those that were rapidly cooled to 600°C by water cooling at two levels: within the time calculated using the above experimental formula and beyond the calculated time. As shown, coarse grains are locally generated in the materials left to cool in the atmosphere and those cooled to 600°C for more than the time specified in this experimental formula, and coarse particles are generated locally in those cooled to 600°C within the time specified in this experimental formula. No grains were observed.

When both were pickled, the coils left to cool in the atmosphere had thick scales and the pickling speed was slow, requiring immersion in the pickling tank for more than 2 minutes. However, the water-cooled coil was sufficiently descaled within 1 minute of immersion in the pickling bath, and even during subsequent cold rolling, local variations in thickness were observed in the coarse-grained coil, as shown in FIG. In example C-2 of the method of the present invention, the thickness variation is 10μ
Although it was within m, the other cases A-2, B-2, and D-2 also showed fluctuation values similar to C-2.

The magnetic properties after cold rolling and annealing are not significantly different from each other as shown in Table 3, and both the air-cooled material and the water-cooled material were able to obtain better magnetism than the material without self-annealing. As described above, according to the present invention, good magnetic properties can be obtained with a simple self-annealing treatment even for electromagnetic steel materials with low Sl and At (generally products of intermediate grade or lower). At the same time, a product with a good shape after cold rolling can be obtained, so the industrial effect is extremely large.

Table-1 Material acid content (vrt)

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between self-annealing temperature and elapsed time (symbols in the diagram are material coil symbols), and Fig. 2 is a diagram showing the microscopic structure of hot-rolled sheets cooled in the air and with water cooling ((a ) is coil symbol c-1 (air cooled), (b) is coil symbol C-3 (t
a time or more), (a) is the coil symbol C-2 (t, within time)), and Figure 3 is a diagram showing the plate thickness fluctuation state after cold rolling ((a)
is coil symbol c-1, (b) is coil symbol C-3, (
e) is the coil symbol C-2). Patent Applicant: Nippon Steel Corporation Co., Ltd. (Shoulder I°η) No. 2
Mouth 3rd eye

Claims (2)

[Claims] (1) After hot rolling a steel containing 2.0 inches or less of (81+AA), self-annealing the hot-rolled plate, and after the self-annealing 60
A method for manufacturing a non-oriented electrical steel sheet with excellent shape and magnetism, which comprises cooling to 0° C. or lower for a time expressed by the following formula (1), followed by pickling and cold rolling to obtain a product thickness. *”)< (38,2X(st+Az)+0.04X(
Self-annealing temperature) c + Self-annealing time (min) -40) (2) The method according to claim 1, wherein after cold rolling, finish annealing is performed or skin-arm rolling is further performed.