JP2000273592A - Electrical stainless steel for cold forging and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of frequent disconnection at the time of drawing working such as wire drawing and reduction by controlling the crystal grain size of ferritic electrical stainless steel contg. specified amounts of C, Si, Cr, Al and N, and the balance Fe with inevitable impurities to the specified one by wire I drawing at the reduction of area equal to or above the specified one. SOLUTION: The crystal grain size of ferritic stainless steel contg., by weight, <=0.02% C, <=3.5% Si, 6 to 19% Cr, <=2.0% Al and <=0.02% N, and the balance Fe with inevitable impurities is Q controlled to >=4 by wire drawing at >=20% reduction of area. It is suitably subjected to warm working at 20 to 100 deg.C. By subjecting it to wire drawing at >=20% reduction of area, the crystal grains are refined as the reduction of area at the time of wire drawing is higher. When the crystal grains are made larger, the numbers of the crystal grains per unit volume and the grain boundaries are made small, and stress concentrates to improve its toughness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic stainless steel for cold forging in ferrite-based electromagnetic stainless steel wires and wires, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, ferrite-based electromagnetic stainless steels need to have low C and N because of their need for soft magnetic properties. However, at low C and N, the crystal grains are likely to be coarsened by hot rolling, and cracks may occur in cold forging applications.
In the method for straightening low toughness steel pipe as it is cold-worked, as disclosed in Japanese Patent Application Laid-Open Publication No. H10-209, the ductile brittle transition temperature of the material is not less than 20 ° C.
A warm straightening method for low toughness steel pipes characterized by performing a straightening after heating to 0 ° C. or lower has been proposed.

[0003]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. 7-6 / 1995
No. 0354 relates to a method for warm straightening a low toughness steel pipe capable of preventing inner surface cracking in bending straightening without causing deterioration of the machinability of the material as it is cold-worked, and is a ductile brittle transition temperature of 100 ° C. to 200 ° C. It is a method for warm straightening at ℃, and is for preventing internal cracks in bending straightening of steel pipes different from breaking during drawing such as drawing and drawing. Therefore, there is a problem that it cannot be sufficiently obtained as a countermeasure against occurrence of frequent disconnection during drawing such as drawing and drawing.

[0004]

Means for Solving the Problems In order to solve the above-mentioned problems, the inventors have made intensive developments, and as a result, have achieved wire drawing without causing cracks during cold forging and deterioration in magnetic properties of products. Another object of the present invention is to provide an electromagnetic stainless steel for cold forging and a method for manufacturing the same, which reliably prevent disconnection that occurs during drawing such as drawing. The gist of the invention is as follows: (1) C ≦ 0.02%, Si ≦ 3.5%, C
r: Ferritic electromagnetic stainless steel containing 6 to 19%, Al ≦ 2.0%, N ≦ 0.02%, the balance being Fe and unavoidable impurities. An electromagnetic stainless steel for cold forging, characterized by having a grain size of 4 or more by processing at a rate of 20% or more. (2) The method for producing an electromagnetic stainless steel for cold forging according to the above (1), wherein warm working at 20 to 100 ° C is performed.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the component composition of the present invention are described below. C ≦ 0.02% Since soft magnetic properties of ferritic electromagnetic stainless steel are required, it is necessary to set C to be low. However, at low C, the crystal grains are likely to be coarsened by hot rolling, and cracks are generated by cold forging. Therefore, the upper limit is set to 0.02%. Si ≦ 3.5% Si is usually added for deoxidation, and if it is too much, it impairs cold workability. Therefore, the upper limit is set to 3.5%.

Cr: 6 to 19% Cr is a basic element of stainless steel, and is a very important element that imparts corrosion resistance to steel. In order to obtain sufficient corrosion resistance, the amount of Cr added was set to 6% or more. Since the addition of a large amount of Cr increases the cost, the upper limit is set to 19% or less. Al ≦ 2.0% Al is a strong deoxidizing element and an element that enhances corrosion resistance. However, if it exceeds 2.0%, if it is present in the molten steel together with oxygen, a hard oxide is formed at the time of solidification, which impairs machinability. Therefore, it was set to 2.0% or less.

N ≦ 0.02% N decreases the critical cold-compression working property and the deformation resistance property,
Aggressive addition is undesirable because it significantly reduces cold forgeability. However, when the air melting method is used, which is advantageous in terms of production cost, N is contained as an impurity. Therefore, the upper limit of N is set to a value that does not significantly reduce cold forgeability, that is, 0.02% or less. Area reduction of 20% or more Processing with a surface reduction of 20% or more by wire drawing requires wire drawing,
The larger the area reduction rate during drawing, the finer the crystal grains.
However, if the area reduction rate is less than 20%, shape defects occur during cold forging, so the area reduction rate is required to be 20% or more.

The most important feature of the present invention is that the crystal grain size is 4 or more, and the crystal grain size is 4 or more. When the crystal grains are small, the number of crystal grains and grain boundaries per unit volume becomes large, and the stress is reduced. Can be dispersed, but reduces toughness. On the other hand, when the crystal grains are large, the number of crystal grains and crystal grain boundaries per unit volume is reduced, stress is concentrated, and toughness is improved. Therefore, the grain size was set to 4 or more. Warm working at 20 to 100 ° C Performing warm working at 20 to 100 ° C on a low toughness steel material that has been hot rolled cannot prevent wire breakage occurring at the time of drawing or drawing below 20 ° C. Further, if the temperature exceeds 100 ° C., the machinability deteriorates.

[0009]

EXAMPLE A ferritic stainless steel base material containing the chemical components shown in Table 1 was rolled to a base material of φ10 × 30 mm, heated to the temperature shown in Table 1 after being rolled, and then subjected to various drawing and drawing reduction rates during warming. The crystal grain size when changed is shown. At that time, there was no increase in hardness of the steel material and no increase in cutting resistance.
The results of the disconnection conditions that occur during wire drawing and drawing are shown. As shown in Table 1, in Examples Nos. 1 to 10, no disconnection occurred, whereas Comparative Examples Nos.
5 shows the occurrence of disconnection.

[0010]

[Table 1]

[0011]

As described above, by maintaining a crystal grain size of 4 or more by warm drawing with a reduction in area of 20% or more in the low toughness material according to the present invention, disconnection frequently occurs in the past. However, even when drawing processes such as drawing and drawing were performed, there was no occurrence of disconnection, and a stable manufacturing method could be established.

Claims (2)

[Claims] 1. The composition contains, by weight, C ≦ 0.02%, Si ≦ 3.5%, Cr: 6 to 19%, Al ≦ 2.0%, N ≦ 0.02%, with the balance being Fe and In ferritic electromagnetic stainless steel consisting of unavoidable impurities,
An electromagnetic stainless steel for cold forging, characterized in that the steel has a grain size of 4 or more by a process of reducing the area by 20% or more by wire drawing. 2. The method for producing an electromagnetic stainless steel for cold forging according to claim 1, wherein warm working is performed at 20 to 100 ° C.