JP2713346B2 - Stainless steel wire excellent in high strength properties and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a high-strength stainless steel having a high utility value in a wide range of fields requiring a steel wire having properties such as heat resistance, corrosion resistance and high strength characteristics. The present invention relates to a method for manufacturing a wire at low cost.

<Conventional technology> Conventionally, martensitic and ferritic stainless steel wires in the JIS standard are G4309 (stainless steel wire) with a soft No. 2 grade and G 4315 (stainless steel wire for cold heading). Class B is defined in the.

However, these are mildly drawn wires that have been appropriately annealed as a process, and have a tensile strength of at most 100 kg /
mm ² , and no higher strength was reported.

On the other hand, there is a method of increasing the strength by quenching and tempering, but it is hardly practically used as a high-strength steel wire material due to poor workability in addition to defects such as hydrogen embrittlement and aging cracking. .

<Problems to be Solved by the Invention> As described above, since the ferrite single-phase stainless steel wire has a low work hardening coefficient, it is considered impossible to obtain a high-strength material as a spring or rope material by work hardening. Was.

Indeed, at a wire drawing degree of about 80%, the tensile strength is 110k at most
g / mm ² , which is extremely low in strength as compared with SUS304 stainless steel wire rod which is used as a high strength material.

An object of the present invention is to obtain a high-strength stainless steel wire which can be sufficiently used for springs and ropes by adding an extreme degree of 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%, and Cr 11.50%.
~ 18.00%, P <0.03%, S <0.02%, balance Fe
After holding the hot-rolled material of martensitic or ferritic stainless steel consisting of unavoidable impurities in a temperature range where the parent phase becomes a ferrite single phase, it is subjected to continuous annealing treatment to obtain a ferrite single phase structure, and a further 95% JIS G4314
SUMMARY OF THE INVENTION An object of the present invention is to provide a stainless steel wire excellent in high-strength characteristics characterized by imparting a tensile strength equivalent to WPA or more and WPB or less shown in Table 2 of -1977 and a method for producing the same.

<Operation> The heating temperature during the annealing treatment in the above is 750 to 8
50 ° C. is preferred.

The wire treated as described above is subjected to wire drawing using an alloy die or a diamond die so that the total cross-sectional reduction rate is 5% to 25% and the total cross-sectional reduction rate is 95% or more.

In order to effectively utilize the merits of the high-strength material, the total cross-sectional reduction rate is preferably 98% or more.

If 0.6 to 2.0% of Mo is added to the above composition, the corrosion resistance is improved and the grain boundary strength is improved,
This is effective for removing the adverse effects of P, S, and the like.

The reason why the content of P is set to 0.03% or less and the content of S is set to 0.02% or less is that these are impurity atoms which are easily segregated at the grain boundaries. It is.

In addition, the bonding force through the grain boundaries is reduced, which may cause breakage when wire drawing is performed with a total cross-sectional reduction rate of 95% or more.

Therefore, the amounts of P and S are set to the above-mentioned amounts or less. If Mo is further added, the grain boundaries can be further strengthened.

Annealing in the ferrite single-phase region is performed by relaxing the stress concentration remaining in the parent phase of the material or at the grain boundary or releasing dislocations from the trap, and starting with uniform deformation during the subsequent wire drawing. Has an effect.

The reason for setting the temperature condition of the continuous annealing treatment to 750 to 850 ° C. is that when heat treatment is performed at 850 ° C. or more, the amount of martensite increases during cooling, and the wire drawing process involves a large total cross-sectional reduction rate. This is because, if tempering treatment is not performed when performing the tempering, strain cracking easily occurs, and the wire is easily broken.
On the other hand, when the temperature is 750 ° C. or lower, segregation or uneven strain at grain boundaries and inclusions cannot be sufficiently reduced.

Since the stress state has been relaxed by annealing,
There is an effect that uniform deformation is maintained from the start of wire drawing, a uniform layered structure is finally formed, and variation in strength characteristics is reduced.

Therefore, the total cross-sectional reduction rate can be made 95% or more, and the expected strength characteristics can be obtained.

<Example> Hereinafter, the present invention will be described in detail with reference to examples.

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

Using six kinds of steels A to F having the above chemical components,
A wire having a wire diameter of 5.5 mmφ was obtained by hot rolling, and the wire was drawn to 5.0 mmφ with a die.

Subsequently, of the wire drawing using the steel of the above A, the second
The heat treatment and processing shown in the table were performed.

In addition, A-7 has a cross-sectional reduction rate of 12 ± 3% per sheet.
The others were drawn at 20 ± 3% using an alloy die.

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

In Table 2 above, when A-8 was drawn to 1.2 mmφ or less, breakage frequently occurred, and the drawing was interrupted at 1.2 mmφ. However, for other test materials, breakage that was considered to be insufficient in toughness was observed. Did not. In addition, as a result of transmission observation with an electron microscope, it was found that A-8 had martensite.

From the above table, all of the examples of the present invention have high tensile strength,
A tensile strength equivalent to or higher than WPA and equal to or lower than WPB of the high-strength stainless steel wire standard for springs shown in Table 2 of JIS G4314-1977 is shown.

Further, A-7 and A-10 of the comparative example and A-11 of the conventional example were used.
Was insufficient in wire drawing and could only be obtained with low strength.

Comparative Example A-8 has a high tensile strength, but the drawing is low and cannot be put to practical use. Comparative Example A-9 has a low work hardening due to progress of spheroidization of the carbide probably because of too much annealing, and a low drawing. I could only get things.

<Effects of the Invention> As described above, according to the present invention, a martensitic or ferritic stainless steel having a specific component is annealed at an appropriate temperature, and then hardened and tempered by subjecting it to strong wire drawing. It is possible to produce a high-strength stainless steel wire having sufficient tensile strength and drawability without performing any steps.

Claims (5)

(57) [Claims] Claims: 1. C <0.15%, Si <1.0%, Cr 11.50-18.00
%, P <0.03%, S <0.02%, and the remainder is made of martensitic or ferritic stainless steel consisting of Fe and inevitable impurities by wire drawing according to JIS G4314-1977,
A stainless steel wire having a high tensile strength as shown in Table 2 and having excellent high strength properties. 2. C <0.15%, Si <1.0%, Cr 11.50-18.00
%, P <0.03%, S <0.02%, and the balance is martensitic or ferritic stainless steel consisting of Fe and unavoidable impurities. With a ferrite structure, wire drawing with a total cross-section reduction rate of 95% or more
A method for producing a stainless steel wire having excellent high-strength properties, characterized by imparting a tensile strength equivalent to WPA or more and WPB or less shown in Table 2 of JIS G4314-1977. 3. The method according to claim 2, wherein 0.6 to 2.0% of Mo is added as a chemical composition. 4. The method according to claim 2, wherein the continuous annealing is performed at 750 to 850 ° C. 5. The method for producing a stainless steel wire having excellent high-strength characteristics according to claim 2, wherein the cross-section reduction rate per one die in the wire drawing is 5 to 25%.