JPS6296615A - Manufacture of grain oriented electrical sheet superior in magnetic characteristic and less in ear cracking at hot rolling - Google Patents

Abstract

PURPOSE:To manufacture grain oriented electrical sheet less in iron loss and free from ear crack hole at hot rolling, by adding traces of specified Sn, Nb, raising Si content and reducing sheet thickness at manufacturing silicon steel sheet. CONSTITUTION:Silicon steel slab contg. by weight 2.5-4.0% Si, 0.04-0.10% C, 0.04-0.4% Sn, 0.002-0.06% Nb, 0.015-0.040% acid soluble Al, 0.0040-0.0100% N, 0.030-0.150% Mn, 0.015-0.040% S is hot rolled and made to hot rolled plate having 1-5mm thickness by finish hot rolling through soln. heat treatment. This is cold rolled at one time or more contg. final cold rolling of >=80% severe draft, intermediately annealed during them and subjected to well known decarbonization annealing after the final cold rolling. Next, the sheet is coated with annealing separator agent made mainly of MgO and finally finish annealed. Si content is increased, sheet thickness is reduced iron loss is decreased and stabilization of secondary crystal is improved by Sn addition, and Nb is added to manufacture low iron loss grain oriented electrical sheet free from ear cracking at time of hot rolling.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is directed to the development of high magnetic flux density unidirectional electrical steel sheets with less edge cracking during hot rolling (excellent iron loss characteristics), which are used in iron cores of transformers, etc. It's about manufacturing.

[Conventional technology]

Unidirectional electrical steel sheets are soft magnetic materials that are mainly used as iron core materials for transformers and other electrical equipment, and their magnetic properties must have good excitation properties and iron loss properties.

Bll (magnetic flux density at a magnetic field strength of 800 A/m) is usually used as a numerical value representing this excitation characteristic, and W17150 (1.
The iron loss per 1 kg when magnetized to 77) is used.

This unidirectional electromagnetic 11 plate is usually obtained by utilizing a secondary recrystallization phenomenon to develop a so-called Goss structure having a (110) plane and a <001> axis in the rolling direction on the steel plate surface. In order to obtain good magnetic properties, it is important that the <001> axis, which is the axis of easy magnetization, is highly aligned in the rolling direction. In addition, the plate thickness, grain size, specific resistance, surface coating, purity of the steel plate, etc. have a large influence on the magnetic properties.

The directionality has been greatly improved by the method of using ^IN and MnS as inhibitors (Japanese Patent Publication No. 1566/1972) and the method of using MnSe or MnS and sb as inhibitors (Japanese Patent Publication No. 1349/1982). However, the iron loss characteristics have also improved significantly. In addition, other inhibitor constituent elements include Pb and S.
b. Method using Nb + Te (Special Publication No. 38-82
14), Zr, Tt+ a, Nb+ Ta
, V+ Cr+ M.

(Japanese Unexamined Patent Publication No. 52-24116),
Nb.

Method of using Ti (Japanese Unexamined Patent Publication No. 14858/1983)
A method using Sn (Japanese Patent Publication No. 57-9419) has been proposed.

On the other hand, due to the rise in energy prices in recent years, transformer manufacturers have increasingly focused on materials for low core loss transformers. Amorphous alloy and 6.5% as low iron loss materials
Although Si steel and other materials are being developed, there are still problems that need to be solved before they can be used industrially as materials for transformers. Therefore, efforts have been made to reduce iron loss by reducing the thickness of grain-oriented electrical steel sheets and increasing the amount of Si to increase specific resistance as a method for achieving a low iron-lateral ratio.

It has long been known that reducing the thickness of steel sheets and increasing the amount of Si in the steel is effective in reducing iron loss, but both of these methods require secondary recrystallization. The plate thickness and Si content have been limited for reasons such as causing instability. A.I.N.

The method of adding Sn to the manufacturing method using MnS as an inhibitor (Japanese Patent Publication No. 57-9419) is extremely effective in stabilizing secondary recrystallization, and is effective in reducing the thickness of the plate and increasing the amount of Si. The conventional board thickness of 0.30 to 0.35 va has been improved to 0.15 to 0.23.
The conventional Si content of 2.9 to 3.1% was added to Tsuru by 3.2 to 3.5%.
This made it possible to manufacture products with excellent iron loss characteristics.

However, when increasing the amount of Si, the carbon content is increased in accordance with the amount of Si in order to obtain an appropriate structure of the hot rolled sheet, and the amount of T in the steel sheet during hot rolling is almost the same as when the amount of Si is low. However, the amount of Si has increased. Si has a different solubility between α and T, and has a tendency to segregate near grain boundaries during hot rolling where α-γ transformation and T-α transformation occur, causing internal cracks and chipping of the edges of hot-rolled sheets ( ear cracking).

Furthermore, since Sn segregates at grain boundaries, it tends to promote edge cracking. In other words, the method of adding Sn to increase the amount of Si to improve iron loss characteristics has the drawback of increasing edge cracking during hot rolling and causing a decrease in yield.

c) Problems to be Solved by the Present Invention] The present invention solves the problem of secondary The present invention provides a method for solving the problem that since Sn is added to stabilize recrystallization, edge cracking during hot rolling increases and the yield decreases.

[Means for solving problems]

The present invention has succeeded in increasing the amount of Si by adding Sn and reducing the amount of iron by reducing the plate thickness, and at the same time, by adding Nb, it has succeeded in reducing edge cracking during hot rolling and improving yield. The present invention provides a method for manufacturing a magnetic steel sheet.

The present invention will be explained in detail below.

The present inventors focused on the fact that the addition of Sn is an effective means to facilitate measures to reduce iron loss by increasing the amount of Si and decreasing the sheet thickness, and the inventors focused on the fact that the addition of Sn is an effective means of facilitating measures to reduce iron loss by increasing the amount of Si and decreasing the sheet thickness. As a result of searching for a means to solve this increase, it was discovered that by adding a small amount of Nb to the steel, it was possible to achieve the desired purpose and produce unidirectional electrical steel sheets with excellent magnetic properties and less edge cracking during hot rolling. They discovered this and completed the present invention.

The reasons for specifying the components of the slab as a starting material in the present invention will be explained below.

If the St content exceeds 4%, embrittlement becomes severe and cold rolling becomes difficult, which is not preferable. On the other hand, if it is less than 2.5%, the electrical resistance is low and it is difficult to obtain good iron loss characteristics.

If C is less than 0.04%, it is difficult to obtain a suitable primary recrystallized m-weave, resulting in an incomplete secondary recrystallized structure.

On the other hand, if it exceeds 0.10%, decarburization will be insufficient, which is not preferable.

If Sn is less than 0.04%, the effect of finely precipitating MnS etc. and improving the precipitated dispersed phase is not sufficient. On the other hand, if it exceeds 0.4%, the forsterite coating deteriorates, which is not preferable.

Nb is an element that characterizes the present invention, but if the amount added exceeds 0.06%, instability of secondary recrystallization will occur.
If it is less than 0.02%, the effect of reducing edge cracking in hot rolled pieces is not sufficient.

Acid-soluble Al and N are the basic components for obtaining the main inhibitor ^IN, which is essential for obtaining high magnetic flux density in the present invention, and if they are outside the above range, secondary recrystallization becomes unstable, which is undesirable. is 0.015 to 0.04
0%, and N is 0.0040 to 0.0100%.

In addition, Mn and S are elements necessary to form the inhibitor MnS, and if they are out of the above range, secondary recrystallization becomes unstable, which is not preferable, so Mn is 0.030 to 0.
．． 150%, and S is set at 0.015 to 0.040%.

Furthermore, in the present invention, 0.005 to 0.04% Se.

0.001-0.4% Cr+Ni1Mo,
It is permissible for the material of the present invention to contain one or more of S b r Cu +As, Bi, and the like.

The molten steel with the above components is processed by ingot making, blooming rolling or continuous casting.
0 to 400 ta-thick slab, and in the subsequent hot rolling, 1300 to 1400 ta to dissolve Mns etc.
After being held at ℃ for several hours, it is roughly rolled to a thickness of 20 to 60++v+, and then finished rolled to a hot rolled sheet of 1 to 5II11 thickness. The finishing temperature of hot rolling is 900 to 1100°C. This hot-rolled sheet is annealed at 700 to 1200° C. as necessary, and cold rolled at least once including final cold rolling with a reduction ratio of more than 80%, and intermediate annealing is performed in between. Intermediate annealing before final cold rolling is performed at 900-1200℃ as necessary.
50 to 50 seconds between multiple passes in the cold rolling process, which is held for 30 seconds to 30 minutes and then rapidly cooled to control the precipitation of AIN.
By performing aging treatment at 400°C, even better magnetic properties can be obtained. After the final cold rolling, a known decarburization annealing is performed, and Mg
An annealing separator mainly composed of O is applied, and Nt is applied in the subsequent final finish annealing.

A steel plate is heated to 100° C. or higher in N2 or a mixed gas thereof and held for several hours. Even better magnetic properties can be obtained by performing annealing for the purpose of adding tension after the final finish annealing.

The present inventors determined the appropriate range of the above Nb amount through the following experiments.

First, the inventors obtained St = 3.25 by vacuum melting.
%, C=0.07%, 5olA l 0.027%,
N=0.008%, Mn=0.08%, S=0.0
27%, 5n=0.12%, Nb=0.002~0
．． An ingot containing 0.094% or <0.001% of residual Fe was prepared, and after adjusting the material to a thickness of 40 mm by blooming rolling, it was placed in a heating furnace and held at 1350°C for 90 minutes, and rolling was started at 01150°C. Finish to 15m (reduction rate 63%) in one pass. ■After starting rolling at 1200℃, finish into 2.3 cranes in 6 baths (finishing exit temperature 1050℃)
Two types of hot rolling experiments were conducted. FIG. 1 shows the relationship between the maximum edge crack depth and the amount of Nb in a one-pass rolled material.

As shown in FIG. 1, it can be seen that the edge cracking is reduced when the Nb content is 0.002%. For hot-rolled sheets finished with a 6-pass reduction of 2.3 mm, N290% and N210% will continue to be used.
After being held at 1130°C for 30 seconds in a mixed gas of The obtained cold-rolled sheet was decarburized and annealed by a known method, coated with a seizing separator, finished annealed, and then tension-coated to obtain a unidirectional electrical steel sheet. The magnetic properties of the product are shown in Figure 2.As shown in Figure 2, Nb>
It can be seen that when the content is 0.06%, the magnetism deteriorates. 1st
From the results shown in Figure and Figure 2, the amount of Nb is 0.002 to 0.06%.
I understand what I should do.

Although the reason for the new finding that Nb is effective in reducing ear cracking is not necessarily clear, the present inventors speculate as follows. One of the important points when considering the mechanism of edge cracking during hot rolling is α-γ transformation. S
Since the solid solubility of , St is larger in the α phase than in the T phase, α-γ transformation and γ-α transformation during hot rolling are considered to be one of the major causes of segregation of S and St. Segregation of S and St occurs in or near the phase that has undergone transformation, and it is thought that this tendency is noticeable at grain boundaries. Segregation of S and St at or near grain boundaries is thought to cause internal cracks. It is also thought that the difference in deformation between the α phase and the γ phase is a cause of stress non-uniformity and metal flow non-uniformity. On the other hand, since tension is applied to the edges in the width direction (edges) in the rolling direction, there is a high possibility that cracks will occur if internal cracks or uneven metal flow occur. As a result, the α-γ transformation partially occurs during hot rolling in the steel that was maintained at 1350 to 1400°C and had an α single phase before hot rolling, resulting in α.

It is thought that the fact that processing is applied while in the γ two-phase state itself causes cracks to occur at the ends.

On the other hand, Nb is an α-stabilizing element, which affects the α-γ transformation and stabilizes α, thereby making the metal flow uniform during hot rolling, and as a result effective in reducing edge cracking during hot rolling. It is assumed that he worked in Figure 3 shows the relationship between edge cracking and Nb content in the 6-pass hot-rolled material in this experiment. As can be seen from FIG. 3, Nb addition is very effective in reducing edge cracking.

Furthermore, Nb is a nitride-forming element, and as shown in FIG. 2, when Nb>0.06%, it is thought that the precipitation of NbN has an adverse effect on the precipitation of r+lN, resulting in deterioration of magnetism.

Examples will be described below.

[Example 1] Si = 3.26%, C = 0.0 by vacuum melting
69%, acid soluble A l = 0.026%, N = 0
．． 0080%.

Mn = 0.076%, S = 0.028%, Sn
=0.12%.

Cu = 0.077%, Nb = 0.019.0.0
An ingot containing 40.0.090 or <0.001% with residual Fe is created, and the material is adjusted to a thickness of 40 mm by blooming rolling, then placed in a heating furnace and the material is heated to 1350 mm.
After being held at 1200° C. for 90 minutes, it was air cooled and hot rolled for 6 baths from 1200° C. to obtain a hot rolled sheet with a thickness of 2.3 fl. The finishing temperature of hot rolling was 1000-1100°C. The hot rolled sheet was successively processed under the following three conditions to obtain a unidirectional electrical steel sheet.

(1) Hot-rolled plate annealing (0 after holding the image at 1130℃ for 30 seconds)
Rapid cooling by holding at 0℃ for 1 minute) - Cold rolling under strong reduction (0,285
am finish) - Decarburization annealing (held at 850°C for 150 seconds) -
Annealing separator application - Final finish annealing (held at 1200°C for 20 hours) - Tension coating (2) Finish plate thickness of strong reduction cold rolling is 0.225 m, other conditions are (same as 11 (3) Hot-rolled plate annealing (quenched after holding at 1000℃ for 3 minutes) -
Cold rolling (1,25mm finish) - Intermediate annealing (1130
℃ for 30 seconds, then held at 850℃ for 1 minute and quenched) - Strong reduction cold rolling (0,175w5 finish) - Conditions for subsequent processing are (see 11. Edge cracking in the same hot rolled sheet and magnetic properties of the finished product) The first result is
1 Table [Example 2] By vacuum melting Si = 3.50%, C = 0.
078%, acid soluble Att = 0.027%, N
=0.0083%.

Mn −0,080%, S = 0.026%,
Sn=0.10%.

Cr = O, 050%, Cu = 0.070%,
Nb = Q, OIQ.

An ingot containing 0.080 or <0.001% with residual Fe is prepared, and after adjusting the material to a thickness of 401 by blooming, the material is placed in a heating furnace and heated to 1380°C for 60 minutes.
After being held for 20 minutes, it was cooled in air and hot-rolled from 1200°C for 6 rolls to obtain a hot-rolled plate with a thickness of 2.3. The finishing temperature of hot rolling was 1050-1100°C. The hot rolled sheet was successively treated under the following two conditions to obtain a unidirectional electrical steel sheet.

(1) Hot-rolled plate annealing (85℃ after holding at 1125℃ for 30 seconds
Rapid cooling by holding at 0℃ for 1 minute) - cold rolling under strong reduction (0,22
5m finishing) - Decarburization annealing (held at 850℃ for 150 seconds) →
Annealing separator application - final finish annealing (held at 1200℃ for 20 hours) → tension coating (2) cold rolling (1,55fl finish) → intermediate annealing (1
Hold at 125℃ for 30 seconds, then hold for 1 minute and quench) - Strong reduction cold rolling (0,225m finishing) → Subsequent processing conditions are (
Table 2 shows the results of edge cracking in the same hot rolled sheet and magnetic properties of the finished product.

Table 2 [Effects of the Invention] As described above, according to the present invention, by adding a small amount of Nb to unidirectional silicon steel, it is possible to prevent edge cracking caused by hot rolling while maintaining excellent magnetic properties. Since it is possible to prevent a decrease in yield, it has a great industrial effect.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between Nb content and edge cracking during hot rolling.
The figure is a diagram showing the relationship between the amount of Nb and magnetic properties, and FIG. 3 is a metal mm photograph showing the relationship between the amount of Nb and edge cracking during hot rolling.

Claims (1)

[Claims] Si: 2.5-4.0%, C: 0.04-0 by weight
．． 10%, Sn: 0.04-0.4%, Nb: 0.00
2-0.06%, acid-soluble Al: 0.015-0.04
0%, N: 0.0040-0.0100%, Mn: 0.
030-0.150%, S: 0.015-0.040%
A silicon steel material slab containing
% or more of cold rolling including final cold rolling with heavy reduction, intermediate annealing performed in between, and decarburization annealing after final cold rolling;
A method for producing a unidirectional electrical steel sheet with excellent magnetic properties and less edge cracking during hot rolling, characterized by subjecting it to final annealing.