JPH02240242A - Stainless steel wire having excellent high strength characteristics and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture the stainless steel wire having excellent high strength characteristics of specified tensile strength at low cost by subjecting a stainless steel wire of ferrite structure having specified compsn. constituted of C, Si, Cr, P, S and Fe to wire drawing at extreme reduction ratio. CONSTITUTION:A hot rolled wire material or a wire stock after subjected to pre-wire drawing of a martensitic or ferritic stainless steel contg. <0.15% C, <1.0% Si, 11.50 to 18.00% Cr, <0.03% P and <0.02% S, furthermore admixed, at need, with 0.6 to 2.0% Mo and the balance Fe with inevitable impurities is subjected to continuous annealing treatment into ferrite structure. This treatment is executed preferably at 750 to 850 deg.C. The obtd. stainless steel wire of a ferrite single phase is furthermore subjected to wire drawing accompanied with >=95% cumulative reduction in area. In this way, tensile strength equivalent to WPA to WPB shown in a table 2 of JIS G4314-1977 is imparted, by which the high strength stainless steel wire sufficiently usable for springs and ropes can be obtd.

Description

[Detailed Description of the Invention] <Industrial Application Fields> The present invention provides high-strength stainless steel that has high utility value in a wide range of fields that require steel wires that have properties such as heat resistance, corrosion resistance, and high strength characteristics. The present invention relates to a method of manufacturing wire at low cost.

<Conventional technology> Conventionally, according to JIS standards, martensitic and ferritic stainless steel wires are classified as G 4309 (
Soft No. 2 is used as a heat treatment for stainless steel wire,
Class B is specified for 15 (stainless steel wire for cold heading).

However, these are light wire drawings with appropriate annealing as a process, and the tensile strength is at most loo.
kg/+am", and no one with even higher strength has been reported.

On the other hand, there is a method to increase the strength by quenching and tempering, but it is hardly put to practical use as a high-strength steel wire material due to drawbacks such as hydrogen embrittlement and age cracking and poor workability. .

<Problem to be solved by the invention> As mentioned above, single-phase ferrite stainless steel wire has a low work hardening coefficient, so it is considered impossible to obtain high strength materials for springs and lobe materials through work hardening. Ta.

It is true that at a wire drawing degree of about 80%, the tensile strength is at most 11.
0 kg/mm'', which is extremely low strength compared to 5OS304 stainless steel wire, which is used as a high-strength material.

This invention aims to obtain a high-strength stainless steel wire that can be sufficiently used for springs and lobes by adding the utmost degree of wire drawing to a ferrite single-phase stainless steel wire.

Means for Solving the Problems〉 That is, the present invention provides C<0.15%, Si<1.0%,
Cr11.50-18.00%, P<0.03%, S<
A hot-rolled material of martensitic or ferritic stainless steel containing 0.02% Fe and unavoidable impurities is held in a temperature range where the matrix becomes a single ferrite phase, and then subjected to continuous annealing treatment. A wire drawing process with a total area reduction rate of 95% or more is performed to give a tensile strength equivalent to WPA or more and WPB or less as shown in Table 2 of JIS G4314-1977. The present invention aims to provide a stainless steel wire with excellent high strength characteristics and a method for manufacturing the same.

Effect〉 In the above, the heating temperature during annealing treatment is 750~
850°C is preferred.

The wire treated as described above is drawn using an alloy die or a diamond die, with a cross-sectional reduction rate of 5 to 25% per die and a total cross-sectional reduction rate of 95% or more.

In order to make effective use of its merits as a high-strength material, it is preferable that the total cross-sectional reduction rate be 98% or more.

Furthermore, if 0.6 to 2.0% Mo is added to the above composition, the corrosion resistance will be improved and the grain boundary strength will be improved, which is effective in removing the negative effects of P, S, etc. .

The reason why the amount of P is 0.03% or less and the amount of S is 0.02% or less is that these are impurity atoms that tend to segregate at grain boundaries, and when they segregate, they lower grain boundary energy and deteriorate grain boundary strength. This is because it will happen.

Furthermore, the bonding strength through the grain boundaries becomes low, which may cause breakage when wire drawing is performed with a total area reduction rate of 95% or more.

Therefore, the amounts of P and S are set to be equal to or less than the above-mentioned C. Furthermore, by adding Mo, it is possible to further strengthen the grain boundaries.

Annealing in the ferrite single phase region relieves the stress concentration remaining in the parent phase of the material or at the grain boundaries, or releases dislocations from traps, so that the subsequent wire drawing process starts with uniform deformation. have an effect.

In addition, the temperature conditions for continuous annealing treatment are 750 to 850℃.
℃ refers to when heat treatment is performed at 850℃ or higher,
This is because the amount of martensite increases during cooling, and when wire drawing is performed with a large total cross-section reduction rate, strain cracks easily occur and wire breakage occurs easily if tempering is not performed. On the other hand, if the temperature is 750'C or less, segregation or unrestrained strain in grain boundaries and inclusions cannot be sufficiently relaxed.

Since the stress state is relaxed by annealing, uniform deformation is maintained from the start of wire drawing, and a homogeneous layered structure is finally formed, which has the effect of reducing variations in strength properties.

Therefore, it is possible to increase the total area reduction rate to 95% or more, and the expected strength characteristics can be obtained.

<Example> The present invention will be explained in detail below with reference to Examples.

First, Table 1 shows the compositions of the steels used in the Examples, Comparative Examples, and Conventional Examples of the present invention.

1. Obtain a front wire rod and use a die to cut it into 5. Wire drawing was carried out to On+mφ.

Subsequently, the wire drawing using the above-mentioned steel A was subjected to the heat treatment and processing shown in Table 2.

In addition, for A-7, the cross-sectional reduction rate per sheet is 12 ± 3%,
The other wires were drawn using an alloy die at 20±3%.

Table 2 also shows the effects of mechanical properties after wire drawing.

Second! I Using six types of steel A-F having the above chemical composition, each is hot rolled and drawn to a wire diameter of 5.5 msψ in Table 2 above, A-8 is 1.2 mmφ or less, Due to frequent wire breakage, we stopped the wire drawing at 1.2mmφ.
Regarding the other test materials, no wire breakage, which may be due to insufficient toughness, was observed. In addition, as a result of transmission observation using an electron microscope,
It became clear that martensite was generated in the sample A-8.

From the above table, all of the examples of the present invention have high tensile strength.
It exhibited a tensile strength equivalent to WPA or more and WPB or less of the high-strength stainless steel wire standard for springs shown in JIS G4314-1977 Table 2.

In addition, comparative examples A-7 and A-10 and conventional example A-
In No. 11, only low strength could be obtained due to insufficient wire drawing.

Comparative Example A-8 has high tensile strength but low reduction of area (and cannot be put into practical use), and Comparative Example A-9 has low work hardening due to progress of spheroidization of the carbide probably due to excessive annealing (and low reduction of area). I could only get a low value.

<Effects of the Invention> As explained above, according to the present invention, martensitic or ferritic stainless steel having specific components is annealed at an appropriate temperature and then subjected to strong wire drawing, thereby making it possible to harden and temper the stainless steel. High-strength stainless steel wire with sufficient tensile strength and drawing characteristics can be manufactured without performing any additional steps.

Claims (5)

[Claims] (1) C<0.15%, Si<1.0%, Cr11.5
JIS G4314- 1977, a stainless steel wire with excellent high-strength properties and having the tensile strength shown in Table 2. (2) C<0.15%, Si<1.0%, Cr11.5
Hot-rolled or underdrawn wire of martensitic or ferritic stainless steel containing 0 to 18.00%, P < 0.03%, S < 0.02%, and the remainder consisting of Fe and unavoidable impurities. The wire is continuously annealed to form a ferritic structure, and then drawn with a total area reduction rate of 95% or more to achieve a tensile strength equivalent to WPA or more and WPB or less shown in Table 2 of JIS G4314-1977. A method for producing stainless steel wire with excellent high-strength characteristics. (3) The method for producing a stainless steel wire having excellent high strength characteristics according to claim (2), wherein 0.6 to 2.0% of Mo is added as a chemical composition. (4) The method for producing a stainless steel wire with excellent high strength properties according to (2), wherein the continuous annealing treatment is carried out at 750 to 850°C. (5) The method for manufacturing a stainless steel wire with excellent high strength properties according to claim (2), wherein the cross-section reduction rate per die during wire drawing is 5 to 25%.