JPH04107215A - Production of hot rolled plate for silicon steel sheet - Google Patents

Abstract

PURPOSE:To produce a hot rolled plate for silicon steel sheet where recrystallization and grain growth are sufficiently completed by subjecting a slab for silicon steel sheet containing specific percentages of C, Si, and Al to hot finishing and to heating and holding at respectively specified temps., performing cooling, and then coiling the resulting plate at specific temp. CONSTITUTION:At the time of producing a hot rolled plate by hot-rolling a slab for silicon steel sheet containing, by weight, <=0.005% C, <=4.0% Si, and <=1.0% Al, hot finishing temp. is regulated to 800-950 deg.C, and the resulting plate is heated and held, directly after hot finish rolling, at a temp. higher by >=50 deg.C than the hot finishing temp. for 1-10sec, cooled, and coiled at <=650 deg.C. By this method, a silicon steel sheet having uniform and superior magnetic properties can easily be obtained with certainty under high economical efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a hot-rolled sheet for electrical steel sheets, and more particularly, to a method for manufacturing a hot-rolled sheet as a material for non-oriented electrical steel sheets.

(Conventional technology) Hot-rolled electrical steel sheets are produced by heating a slab, hot rough rolling it, and
Next, the hot-rolled sheet is manufactured by a step of hot finish rolling and then winding, and then the hot-rolled sheet is pickled, cold-rolled, and annealed to become an electrical steel sheet.

In order to obtain good magnetic properties as an electrical steel sheet, it is necessary to complete recrystallization and grain growth during the production of the above-mentioned hot rolled sheet, so the hot finishing temperature is set to a high temperature and the winding temperature is set to 800°C. The method of raising the temperature to a certain degree is often used.

However, according to this method, oxides are dispersed and precipitated at the grain boundaries on the surface of the hot-rolled sheet due to changes in the surface scale and subscale, which significantly reduces pickling properties. This process causes the surface texture to deteriorate. In addition, the temperature distribution during cooling of the coil after winding becomes uneven, and incomplete recrystallization remains, resulting in large fluctuations in deformation resistance, making it difficult to stably perform cold working such as cold rolling. Furthermore, there is a problem that the magnetic properties of the electrical steel sheet become non-uniform.

As a countermeasure, is there a method of manufacturing a hot-rolled sheet at a winding temperature of 650°C or less and subjecting it to recrystallization annealing?
This recrystallization annealing has disadvantages such as lower economic efficiency and a complicated process.

Therefore, a solution to this problem was considered, and
A method described in Japanese Patent No. 138014 has been proposed. In this method, after hot finishing rolling and before winding, holding at a temperature of 650°C or higher for 30 seconds to 5 minutes on a hot run table,
It is wound at a temperature of less than 00°C. However, due to the line speed in hot finish rolling, it is difficult and impractical to hold the roll on the table for a long time as described above.

In contrast, as a solution with high possibility of implementation,
A method described in Japanese Patent No. 2-61644 has been proposed. The method includes a hot finishing temperature of 1000°C or higher, and
After hot finish rolling, water is not poured for 1 to 7 seconds, and then water is poured to cool the sheet and then rolled up at a temperature of 700° C. or less.

(Problem to be solved by the invention) However, the above method has the following problems. In other words, in order to achieve a hot finishing temperature of 1000"C or higher, the slab heating temperature must be 1300"C with practical equipment.
This results in a significant increase in thermal energy, as well as an increase in the amount of solid solution of S, leading to deterioration of material properties after hot rolling. It should be noted that as a countermeasure against property deterioration, it is better to reduce the S content to 0.0015 wt% or less. In reality, it is technically extremely difficult to control the S content to such a low level, and it also greatly reduces economic efficiency. This will lead to a significant decline.

The present invention has been made in view of these circumstances, and its purpose is to solve the above-mentioned problems of the conventional ones, and to solve the problem of deterioration in characteristics such as pickling properties of hot-rolled sheets. It is an object of the present invention to provide a method for manufacturing a hot-rolled electrical steel sheet in which recrystallization and grain growth can be completed without causing a significant decrease in economic efficiency due to an increase in heat energy or the like.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for manufacturing a hot-rolled electrical steel sheet having the following configuration.

That is, the method for manufacturing a hot-rolled electrical steel sheet according to the present invention includes C
: 0.005wt% or less, Si: 4.0wt%
Hereinafter, when hot rolling a slab for electrical steel sheet containing Al: 1.0 wt% or less to produce a hot rolled sheet, the hot finishing temperature is set at 800 to 950°C, and the hot finishing temperature is set at 800 to 950°C. This is a method for producing a hot-rolled electrical steel sheet, which comprises heating and holding at a temperature 50° C. or more higher than the finishing temperature for 1 to 10 seconds, then cooling, and winding at a temperature of 650° C. or lower.

(Function) The present invention heats a slab for an electromagnetic steel sheet containing C, Si, and AI, performs hot rough rolling, then hot finish rolling at various hot finishing temperatures, and then heats the slab before cooling. The hot rolled sheet is heated (hereinafter referred to as reheating) under various heating conditions (i.e., heating temperature and heating holding time), then cooled and rolled up to form a hot rolled sheet, and then the hot rolled sheet is pickled. , cold-rolled, annealed and purified into electrical steel sheets, and investigated the pickling properties, recrystallization and grain growth conditions of the hot-rolled sheets, as well as the magnetic properties of the electrical steel sheets, and based on the following findings obtained as a result:・(It is a thing.

That is, when the hot finishing temperature is set to 800 to 950"C and the temperature is reheated and held for 1 to 10 seconds at a temperature 50"C or more higher than the hot finishing temperature immediately after hot finish rolling, sufficient reheating is achieved by the reheating. Crystal and grain growth occurs, so even if the material is cooled after reheating and rolled up at a relatively low temperature (for example, 500°C or the lowest possible winding temperature), recrystallization and grain growth will not be fully completed. As a result, it was found that the magnetic properties of the electrical steel sheet could be improved. For example, in Figure 1, as a slab for electrical steel sheet, C: 0.0040
wt%, Si: 1.12wt%, Al: 0.002
wt%, Mn: 0.20wt%, S: 0.006
wt% composition, the heating holding time immediately after hot finish rolling was 2 seconds, and the winding temperature was 650°C. This shows the effect of the difference between the reheating temperature and the hot finishing temperature, and the hot finishing temperature is 800 to 950°C, and the reheating temperature is 50°C or more higher than the hot finishing temperature immediately after hot finishing rolling. It can be seen that good magnetic properties can be obtained by heating.

In addition, when winding is carried out at a temperature of 650°C or lower, the dispersion and precipitation of oxides at the grain boundaries on the surface of the hot-rolled sheet due to changes in the surface scale and subscale will not occur, resulting in a decrease in pickling properties. It was found that the magnetic properties of the electromagnetic steel sheet are uniform because the temperature distribution during cooling of the coil is uniform.

Therefore, the method for manufacturing a hot rolled electrical steel sheet according to the present invention is as follows:
As mentioned above, C: 0.005wt% or less, Si: 4
, 0 wt% or less, Al: 1.0 wt% or less, when hot rolling a slab for electrical steel sheet to produce a hot rolled sheet, the hot finishing temperature is set to 800 to 950 ° C., and the hot finishing rolling is carried out. Immediately after, it is heated (reheated) and held at a temperature 50° C. or more higher than the hot finishing temperature for 1 to 10 seconds, then cooled and wound up at a temperature of 650° C. or less.

Therefore, based on the above knowledge, it is now possible to produce a hot-rolled sheet for electrical steel sheets in which recrystallization and grain growth have been sufficiently completed without causing deterioration in properties such as pickling properties of the hot-rolled sheet. . In addition, since the hot finishing temperature is 800 to 950°C, the slab heating temperature may be relatively low, and the reheating immediately after hot finishing rolling is simply held at a temperature higher than 50°C for 1 to 10 seconds. Therefore, it can be implemented without causing a decrease in economic efficiency due to a significant increase in thermal energy.

The hot finishing temperature was 800 to 950°C.
If the heating temperature is lower than 950°C, unrecrystallized or residual particles may remain, resulting in poor magnetic properties of the electromagnetic steel sheet.
This is because it is necessary to raise the temperature to a high temperature of 250° C. or higher, which leads to an increase in thermal energy and deteriorates grain growth, thereby degrading the magnetic properties of the electrical steel sheet.

be.

The reheating temperature immediately after hot finishing rolling is 50° lower than the hot finishing temperature.
The reason why the temperature is set higher than 50°C is because recrystallization and grain growth cannot be completed by increasing the temperature lower than 50°C. The reason for setting the reheating holding time to 1 to 10 seconds is that recrystallization and grain growth can be completed in less than 1 second, and if it exceeds 10 seconds, the properties of the surface scale and subscale after winding will deteriorate. This is because the pickling property deteriorates.

The reason why the winding temperature was set to be 650°C or lower is that if it exceeds 650°C, oxides will disperse and precipitate at the grain boundaries on the surface of the hot rolled sheet due to changes in the surface scale and subscale, resulting in a decrease in pickling properties. This is because the uniformity of magnetic properties is reduced.

The reason why the amount of C is 0.005wt% or less is 0.005w
This is because if it exceeds t%, magnetic aging occurs, resulting in significant deterioration of magnetic properties.

Is Si an element that increases the patency resistance of steel and improves iron loss?
: Is it necessary to keep it below 4.0wt%?

Like Si, AI is an element added to increase the patency resistance of steel and improve iron loss, and also to deoxidize the steel.
1. If it exceeds Owt%, the steel will become brittle, so AI・1.0
Is it necessary to keep it below wt%?

In addition, the slab heating temperature is set to improve grain growth.
The hot finishing temperature should be the lowest temperature that can be maintained at 800 to 950°C, preferably 1100°C or lower.

Steel with a component system in which α-γ transformation exists (for example, 1 wt% Si
steel), the reheating temperature after hot finish rolling is 1000℃.
If it is too high, the magnetic properties will deteriorate due to transformation, so 100
It is desirable to keep the temperature below 0°C. Furthermore, even in steels with compositions in which αγ transformation does not exist, it is better to set the upper limit to 1000°C from the viewpoint of suppressing the development of surface scale.

If the cooling speed before winding is too slow after reheating after hot finish rolling, the properties of surface scale and subscale will deteriorate in the temperature range in the middle of the cooling process, that is, in the temperature range slightly higher than 650°C. However, since this causes a decrease in the pickling properties of the hot rolled sheet, it is better to increase the cooling rate.

After the reheating, the coil is wound at a relatively high temperature (for example, 800 ° C.) to form a coil, and then the coil is immersed in water and rapidly cooled, so that sufficient recrystallization and grain growth occur due to reheating,
In addition, by cooling the coil, it is possible to prevent the formation of scale properties in a temperature range slightly higher than the above-mentioned 650°C, which prevents deterioration of properties such as pickling properties of hot-rolled sheets and a significant increase in thermal energy. It becomes possible to produce a hot-rolled electrical steel sheet in which recrystallization and grain growth have been sufficiently completed without causing any problems. However, this method requires a water tank for immersing and quenching the coil, a means for transporting the coil to the water tank and immersing it, and also requires an operation of immersing the coil in water for quenching, which reduces economic efficiency and reduces operational efficiency. Therefore, it is inferior to the method according to the present invention in terms of economy and operability.

(Example) Example 1 Table 1 shows two types of electromagnetic steel plate slabs (A,
The chemical components of B) are shown below. These slabs contain C in the composition
The slab thickness is 230 mm.

The above-mentioned slab was heated, hot-rough rolled, then hot-finished rolled, reheated, then cooled and wound to form a hot-rolled plate. At this time, the slab heating temperature, hot finishing temperature, reheating temperature after hot finishing rolling, and winding temperature were varied as shown in Table 2. In addition, after hot finish rolling, the product was cooled and rolled up without being reheated.

Next, the hot-rolled sheet was pickled with 7% hydrochloric acid at 85°C, and
After cold-rolling at a rolling reduction of 50%, annealing was performed at 850° C. for 1 minute to obtain an electrical steel sheet, and the magnetic properties of the electrical steel sheet were investigated. The time required for the pickling was also investigated. The results of these investigations are shown in Table 2.

As can be seen from Table 2, in Comparative Examples 1 and 3, the first winding temperature was high, the time required for pickling was long, and the pickling properties were extremely poor. In Comparative Examples 2 and 4, the winding temperature was low, so the pickling properties were good and the magnetic properties were extremely bad.

In conventional examples 1 and 2, hot-rolled sheets are produced at a winding temperature of 650°C or lower, and before pickling the hot-rolled sheets, the hot-rolled sheets are recrystallized and annealed (heated at 850'C for 1 minute). It has excellent pickling properties and magnetic properties.

Examples 1 and 2 of the present invention have excellent pickling properties and magnetic properties that are equal to or better than those of conventional examples 1 and 2.

(Effects of the Invention) According to the method for manufacturing a hot-rolled electrical steel sheet according to the present invention,?
j! , a heat treatment for electrical steel sheets that satisfactorily completes recrystallization and grain growth without deteriorating properties such as pickling properties and cold workability of rolled sheets, or significantly reducing economic efficiency due to increased thermal energy, etc. It becomes possible to reliably manufacture rolled plates. Therefore, it becomes possible to easily and reliably obtain an electrical steel sheet having uniform and good magnetic properties at high cost.

[Brief explanation of drawings]

Figure 1 is a diagram showing an example of the influence of the temperature in the hot partition and the difference between the reheating temperature immediately after rolling and the hot finishing temperature on the magnetic properties of an electrical steel sheet. It is. Patent applicant: Kamiguchi Steel Co., Ltd. Agent: Akira Kanemaru, patent attorney

Claims (1)

[Claims] (1) C: 0.005wt% or less, Si: 4.0wt%
Hereinafter, when hot rolling a slab for electrical steel sheet containing Al: 1.0 wt% or less to produce a hot rolled sheet, the hot finishing temperature is set at 800 to 950°C, and the hot finishing temperature is set at 800 to 950°C. A method for producing a hot-rolled electrical steel sheet, which comprises heating and holding for 1 to 10 seconds at a temperature 50°C or more higher than the finishing temperature, then cooling and winding at a temperature of 650°C or lower.