JP2002180201A - Steel for hard-drawn wire having excellent fatigue strength and ductility, and hard-drawn wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide steel wire for hard-drawn wire which has excellent fatigue strength and ductility, and is useful as the stock for spring steel wire, PC steel wire, galvanized steel wire and cable steel wire for a suspension bridge, and to provide a drawn wire thereof. SOLUTION: The steel contains 0.10 to 1.5% Ni. After rolling or patenting treatment, the steel is subjected to drawing, and is used as it is.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spring steel wire, PC
The present invention relates to a hard drawn steel material useful as a material for a steel wire, a galvanized steel wire, and a steel wire for a suspension bridge cable, and a drawn wire material thereof, particularly a hard drawn steel material excellent in both fatigue strength and ductility. And its drawn wire.

[0002]

2. Description of the Related Art Steel wire rods are widely used in the above-mentioned various applications. However, in reality, such steel wire rods are intended to have higher strength. For example, when trying to increase the strength of a steel wire used for a spring, as a measure for improving the fatigue strength, it is common to improve the fatigue strength by performing an oil tempering treatment after the wire drawing. . Also, in order to increase the strength of PC steel wire, stranded wire, etc.,
A method of ensuring high strength and good workability by suppressing the amount of proeutectoid cementite in a rolled material (for example, JP-A-6-271937), and defining a fine pearlite structure by defining the patenting treatment conditions (For example, Japanese Patent No. 182067). However, with these methods,
There is a problem that a great deal of cost is required and work is complicated.

[0003] On the other hand, some valve springs designed to have relatively low applied stress include wires made of ferritic pearlite or carbon steel having a pearlite structure to increase strength ("hard drawn wire"). ) Is used at room temperature. Such a hard drawn wire has an advantage that the heat treatment is not required and thus the cost is reduced.

[0004] However, a wire drawn from a ferrite-pearlite structure or a pearlite structure has a drawback of low fatigue properties, and even if such a wire is used as a material, it is not possible to realize a high stress as demanded in recent years. . In addition, such a wire is required to have high strength and higher ductility. However, as the strength increases, the ductility tends to decrease, and it is difficult to combine the two properties.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made under such circumstances, and it is an object of the present invention to provide a steel wire for a spring, a PC steel wire, a galvanized steel, which is excellent in both fatigue strength and ductility. An object of the present invention is to provide a steel material for a hard drawn wire, which is useful as a material of a steel wire for a wire and a cable for a suspension bridge, and a drawn material thereof.

[0006]

The steel material for hard drawn wire of the present invention, which has achieved the above-mentioned object, is characterized in that Ni is 0.10 to 1.5.
%, And has a gist in that it is drawn and used as it is after rolling or patenting. In this steel material, "used as it is" means that it is used without being subjected to a heat treatment for austenitizing after wire drawing.

The hard drawn wire of the present invention, which has achieved the above object, is a drawn wire obtained by drawing the above steel material, and has a wire diameter of 1.5 mm or more and a tensile strength of 1700 MPa.
The above and the point that the average pearlite lamella interval is 200 nm or less are summarized.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have studied from various angles with the aim of realizing a hard drawn steel material capable of achieving the above object. As a result, it has been found that the steel material containing a predetermined amount of Ni achieves the above-mentioned object excellently.

According to the study by the present inventors, N
i found that work hardening accompanying wire drawing was suppressed. As a result, it has been found that the drawing strain for achieving the target strength can be increased, and the width of the lamella ferrite can be reduced after the drawing. And by reducing the width of the lamella ferrite,
The unit of shear fatigue crack generation becomes smaller, and the fatigue life can be improved. In addition, it was also found that as the width of the ferrite is reduced, dislocations are less likely to be accumulated in the ferrite, so that fatigue strength is improved and ductility is also improved.

[0010] The steel material for hard drawn wire of the present invention achieves the above-mentioned effects by including a predetermined amount of Ni as described above. However, in order to exhibit such effects, Ni is 0%. It must be contained at least 10%. However, when the Ni content is excessive, a bainite structure or a martensite structure is generated in rolling, and the wire drawing workability is remarkably deteriorated, and the toughness and ductility are rather lowered. .

The steel material of the present invention can be applied to the above-mentioned various uses, and it is necessary to adjust C, Si, Mn, Cr, V, etc., which are the basic components of the steel material, according to the use. The preferred ranges of these chemical components in the case of PC steel and the reasons therefor are as follows.

C: 0.5 to less than 1.1% C is an indispensable element for securing sufficient strength, and therefore it is necessary to contain at least 0.5% or more. The C content is more preferably 0.55% or more, but if it is contained in excess of 1.1%, toughness and ductility extremely deteriorate.

Si: 0.2 to 2.2% Si is an element necessary as a deoxidizing agent in steelmaking, and is dissolved in ferrite to increase temper softening resistance and improve fatigue strength. It is an effective element. In order to exert such an effect, it is necessary to contain Si in an amount of 0.2% or more. However, if the content exceeds 2.2% and becomes excessive, not only is the toughness and ductility deteriorated, but also the removal of the surface becomes worse. Acid and flaws increase and fatigue strength deteriorates. Note that a more preferable lower limit of the Si content is about 0.5%, and a more preferable upper limit is about 2.0%.

Mn: 0.5 to 1.5% Mn is an element effective for deoxidation at the time of steel making, and is an element that enhances hardenability and also contributes to improvement in strength. In order to exert such effects, Mn must be contained at least 0.5%. However, if Mn is contained excessively, a supercooled structure such as bainite tends to be generated during hot rolling or patenting treatment, and 1.5% because linearity is significantly deteriorated
Should be: Note that a more preferred lower limit of the Mn content is 0.7%, and a more preferred upper limit is 1.0%.

Cr: 0.05-1.0% Cr reduces the pearlite lamella spacing, and after rolling,
Alternatively, it is an element useful for increasing the strength after heat treatment and increasing the strength of the wire. In order to exhibit such effects, the Cr content is preferably set to 0.05% or more. However, if the Cr content is excessive, the patenting time becomes too long, and the toughness and ductility deteriorate. Therefore, the content is preferably 1.5% or less.

V: 0.05 to 0.50% V is an element useful for precipitating carbides and carbonitrides on ferrite in a pearlite structure. In order to exhibit such effects, V must be contained at 0.05% or more, preferably 0.10% or more. However, even if the content exceeds 0.50%, a martensite or bainite structure is generated, and workability is deteriorated.

The basic chemical composition when the steel material of the present invention is applied to PC steel is as described above, and the balance is substantially composed of Fe.
It is also effective to contain about 0.05 to 0.50% of Mo as needed to improve the hardenability. In addition, the steel material of the present invention may contain a trace component other than the above-mentioned various components so as not to impair its properties, and such a steel wire is also included in the scope of the present invention. Examples of the trace components include impurities, particularly unavoidable impurities such as P, S, As, Sb, and Sn.

The target fatigue strength can be achieved by drawing a steel material as described above, and the fatigue strength is increased by increasing the degree of wire drawing and increasing the tensile strength. From such a viewpoint, in the hard drawn wire of the present invention, it is necessary that the tensile strength is 1700 MPa or more. However, when the wire diameter is small, the fracture starting from the non-metallic inclusions increases, and the fatigue strength is rather low. Therefore, the wire diameter of the drawn wire needs to be 1.5 mm or more.

As described above, in order to improve fatigue strength and ductility, the pearlite lamella spacing is reduced,
It is effective to reduce the width of the ferrite. According to the study by the present inventors, it has been found that particularly excellent fatigue strength and ductility can be obtained by setting the pearlite lamella spacing of the drawn wire to 200 nm or less.

The pearlite lamella spacing of the drawn wire is 200 n
In order to reduce the number to m or less, it is preferable to appropriately control the rolling conditions, the patenting treatment conditions, and the like. For example, when rolling
Rolling is completed at 900 to 950 ° C, and winding is started at 10 to 20 ° C / s until the start of winding so that no cause pearlite is generated at a high temperature and no supercooled structure (martensite or bainite) is generated. Cool, take up temperature 750-8
The cooling rate to 450 ° C. was set to 0.5 to 3 so that the transformation was completed at around 50 ° C.
A method of cooling at about ° C / s can be mentioned.

On the other hand, the pearlite lamella interval is set to 200 nm.
As the patenting processing conditions for the following, 90
After heating to 0 ° C. or more and cooling to about 600 ° C. at a cooling rate of about 10 to 15 ° C./s so as not to generate cause pearlite, the transformation was completed at that temperature, and the average area reduction rate was 20%. As described above, a wire drawing process in which the total area reduction rate is 80% or more may be performed.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are not intended to limit the present invention. It is included in the technical range of.

[0023]

EXAMPLES Steel having the chemical composition shown in Table 1 below (steel types A to
F) was melted and hot-rolled to produce a steel wire having a diameter of 9.0 mm. Subsequently, after austenitizing at 910 ° C., a patenting process for completing transformation at 640 ° C. and a wire drawing process were performed to obtain a drawn wire. At this time, in the wire drawing, the tensile strength after wire drawing is 1800 to 200.
The final wire diameter was adjusted to be 0 MPa.

[0024]

[Table 1]

Each of the obtained wires was subjected to a tensile test, and the tensile strength and the elongation were measured. The pearlite lamella spacing and fatigue limit were measured by the following methods.

(Perlite lamella spacing) A vertical section of the wire is embedded and, after polishing, 15% in a 5% alcoholic picrate solution.
After immersion for up to 30 seconds for corrosion, scanning microscope (SE
By M), the 4 / D (D: diameter of the wire) position of the wire was observed. At that position, a photograph was taken at a magnification of 5000 to 10000 times, and a line crossing perpendicularly to each of 10 arbitrary lamellae was drawn, and the lamella interval was measured from the length.
The average value of the points was defined as the average pearlite lamella interval.

(Fatigue limit) Using a steel material obtained by wire drawing, a test piece having a sample length of 650 mm
Blueing treatment was performed at 50 ° C. for 20 minutes, and then two-stage shot peening was performed with an impeller type shot peening machine to apply a compressive residual stress to the surface layer. After that, a strain relief annealing at 220 ° C. for 20 minutes was performed and the test was performed. Then, a Nakamura-type rotary bending fatigue test was performed, and a 10-millimeter rotation test was performed according to the test method of JIS Z2274.
The test stress to be canceled was the fatigue limit ^seven times.

The results are shown in Table 2 below together with the wire drawing rate (area reduction rate). From these results, the following can be considered. First, no. Each of Examples 1 to 5 is an example that satisfies the requirements defined in the present invention, but it can be seen that excellent fatigue strength and ductility are exhibited.

On the other hand, no. Samples 6 and 7 are comparative examples lacking any of the requirements specified in the present invention, and it can be seen that any of the characteristics is deteriorated. That is, N
o. In the case of No. 6, which does not contain Ni, the degree of wire drawing is small, the pearlite lamella spacing is widened, and the fatigue strength is low. Further, since the processing strain is large, the elongation is also reduced. On the other hand, No. In the case of No. 7, since the Ni content was too large, supercooled martensite and bainite were generated during rolling, and the wire was broken during drawing.

[0030]

[Table 2]

[0031]

The present invention is constituted as described above, and is excellent in both fatigue strength and ductility.
A hard drawn steel material and a drawn wire material useful as a material for a steel wire, a galvanized steel wire, and a steel wire for a suspension bridge cable have been realized.

Claims (2)

[Claims] 1. It contains Ni in an amount of 0.10 to 1.5% (mean% by mass, the same applies hereinafter), and is used after being rolled or after a patenting process and then subjected to wire drawing. A steel material for hard drawn wire having excellent fatigue strength and ductility characterized by the following. 2. A wire drawn from the steel according to claim 1, having a wire diameter of 1.5 mm or more and a tensile strength of 1700.
MPa or more, and the average pearlite lamella interval is 200
A hard drawn wire having excellent fatigue strength and ductility, characterized by having a diameter of at most nm.