JPS6114208B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a non-oriented electric iron plate with excellent iron loss and magnetic flux density.

Non-oriented electrical steel sheets are generally manufactured through the following process: steel slab → hot rolling → descaling → cold rolling → annealing → insulation coating treatment (cold rolling and annealing may be repeated in some cases) has been done. The present inventors investigated ways to improve the magnetic flux density and iron loss, especially among the properties of cold-rolled non-oriented electrical steel sheets manufactured by such a process, and found that It has been found that magnetic properties can be greatly improved by coarsening the grains and appropriately controlling the size and dispersion state of carbides.

The present inventors have filed a patent application for a method for improving magnetic flux density by controlling the dispersion state of carbides in hot rolled sheets. (Japanese Patent Laid-Open No. 15725-1572) This method is used to hot-roll a steel slab containing 0.01-0.1% C and 3.5% or less Si, then cold-roll and anneale it to produce non-oriented electrical steel sheets. Then, the coiling temperature after hot rolling is set to 500°C or less, or after hot rolling, it is rapidly cooled and then held at 300 to 500°C to precipitate carbides, and the heating rate during annealing is reduced.
This is a method for producing a non-directional electric iron plate with a high magnetic flux density, characterized in that the magnetic flux density is 100°C/min or more.

According to this method, the magnetic flux density is significantly improved, but since the hot-rolled sheet is coiled at a low temperature or rapidly cooled, the grain size of the hot-rolled sheet tends to become finer, and the iron loss is sufficiently low. It became clear that this was not the case. As a result of further study on this point, the present inventors found that after hot rolling, the crystal grains were coarsened by coiling at a high temperature, and then the carbon was subjected to solution treatment and precipitation treatment to improve the dispersion of carbides. It was discovered that low iron loss and high magnetic flux density can be obtained by controlling the magnetic flux density.

That is, the present invention hot-rolls a steel containing 0.1% or less of C and 3.5% or less of Si, and then cold-rolls and anneales it to produce a non-oriented electrical steel plate. After winding at a temperature of 650℃ or higher, 700℃
Heat to a temperature of 30 seconds or more, then cool to a temperature of 300 to 500 degrees Celsius at a cooling rate of 5 degrees Celsius or more, and
This is a method for producing a non-oriented electric iron sheet with excellent magnetic properties, which is characterized by cooling by holding at ~500°C for 30 seconds or more, followed by cold rolling and annealing.

In the present invention, in order to cause sufficient grain growth after hot rolling, it is necessary to set the coiling temperature to 650°C or higher. In order to obtain proper dispersion of carbides in the subsequent precipitation treatment, it is necessary to solutionize the uniform carbon as described above and then precipitate it at an appropriate temperature. To this end, the following treatment is performed. First, carbon is dissolved by heating it to a temperature of 700°C or more for 30 seconds or more. After that, it is cooled to a temperature of 300 to 500°C at a cooling rate of 5°C/second or more, but if this cooling rate is too slow, some of the solid solution carbon will precipitate at grain boundaries during cooling. This is because a desired degree of supersaturation cannot be obtained. After cooling to 300 to 500°C, it is held at this temperature to allow carbide precipitation to proceed, but the holding time is determined by the cooling rate from 700°C, and the faster the cooling rate, the shorter the precipitation will be completed. However, even in the case of extremely fast cooling rate such as water cooling, 30 seconds or more is necessary.

The hot-rolled steel sheet treated in this way is cooled to a predetermined thickness and then annealed. The faster the heating rate during annealing, the higher the magnetic flux density.
100℃/min or more is desirable. This is thought to be due to the formation of a texture favorable for improving magnetic flux density by rapid heating.
It is also possible to perform cooling two or more times with intermediate annealing in between, and it is also possible to perform decarburization during annealing to further improve iron loss.

The slab heating temperature and hot rolling finishing temperature may be determined according to the usual method, but in order to further improve the magnetic properties, the slab heating temperature should be 1200°C or lower, preferably 1100°C or lower, and the hot rolling finishing temperature should be in the d+y range. It is better to

The reason for limiting the component elements is as follows.
Next, when C exists in large amounts, it deteriorates magnetic properties,
Makes decarburization difficult when performing decarburization annealing. Therefore, it is necessary that the content be 0.1% or less. If Si exceeds 3.5%, cold working will be extremely difficult and rolling will not be possible, so it must be 3.5% or less. In addition to these elements, about 0.1-0.5% Ai, about 0.3-1.0%
It is also possible to add P or the like in an amount of about 0.03 to 0.2% of Mn.

Next, examples of the present invention will be shown together with comparative examples.

Example A steel slab with the components shown in Table 1 was heated at 810℃ (steel 1.2).
After hot rolling at a finishing temperature of 820°C (Steel 2), it was rolled at two levels: 740°C and 600°C. A sample was taken from this coil and held at 750℃ for 1 minute.
300℃, 400℃, 500℃, 700℃ with cooling rate of 30℃/sec
The mixture was cooled to a temperature of °C, held at each temperature for 3.5 minutes, and then cooled to room temperature. This is 75% cold rolled,
After that, decarburization annealing was performed at 800°C. The heating rate during annealing was set at two levels: approximately 800°C/min and 10°C/min. Epstein test pieces were taken from the decarburized and annealed plates, and the magnetic flux density was measured using the method specified in JIS. The results are shown in Figure 1. The magnetic flux density increases when the precipitation temperature is below 500℃, and when it reaches 700℃,
descend. This tendency is observed regardless of the amount of Si and the heating rate, but the absolute value of the magnetic flux density becomes higher in the case of rapid heating. The takeoff temperature mainly has a large effect on the iron loss, and the iron loss decreases in the case of high temperature winding.

[Brief explanation of the drawing]

Figures 1a, b, and c are diagrams showing the relationship between precipitation treatment temperature, magnetic flux density, and iron loss in Examples and Comparative Examples of the present invention for Steels 1, 2, and 3, respectively; The black circle indicates the winding temperature of 740℃.
If the heating rate during annealing is 800℃/min, the white circle mark is 740℃.
℃, 10℃/min, the black triangle indicates 600℃, 10℃/min.
In the case of 800℃/min, the white triangle mark indicates 600℃/min, 10℃/min.
This is the case for minutes.

Claims (1)

[Claims] 1. When producing a non-oriented electrical steel plate by hot rolling steel containing 0.1% or less of C and 3.5% or less of Si, the hot rolled plate is cold rolled and annealed. After coiling at a temperature of 650℃ or higher, heat it to a temperature of 700℃ or higher for 30 seconds or more, and then cool it at a cooling rate of 5℃/second or higher.
A method for producing a non-oriented electric iron sheet with excellent magnetic properties, which comprises cooling to a temperature of 300 to 500°C, holding at 300 to 500°C for 30 seconds or more to cool, and then cold rolling and annealing. 2. A method for producing a non-oriented electric iron plate with excellent magnetic properties as set forth in claim 1, characterized in that the heating rate during annealing is 100° C./min or more.