JPH046211A - Production of steel wire for spring having excellent fatigue strength - Google Patents

Abstract

PURPOSE:To produce the steel wire for springs having excellent fatigue strength by elongating the wire of a high-cleanliness steel specified in the compsn. of nonmetallic inclusions at a specific reduction of area, then subjecting the wire to annealing and tempering treatments. CONSTITUTION:The high-cleanliness steel consisting, by weight %, 0.5 to 0.8% C, 0.8 to 2.5% Si, 0.1 to 1.0% Mn, 0.1 to 2.0% Cr, the balance Fe and unavoidable impurities and contg. the nonmetallic inclusions contg. <=40% Al2O3, 35 to 87% SiO2, <=30% MgO, and consisting of the balance CaO, MnO and unavoidable impurities is used as a blank material. This steel blank material is hot rolled to the wire and thereafter, the wire is drawn at 70 to 95% reduction of area. The wire is subjected to the annealing and tempering treatments and is thereby made into the steel wire for springs having >= 250 kgf/mm<2> strength. One or more kinds of 0.03 to 0.50% V, <= 2.0% Ni, 0.03 to 0.50% Nb, and 0.03 to 0.50% Mo are incorporated into this steel compsn. at need. This steel wire is usable for valve springs for internal combustion engines, clutch springs, brake springs, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a spring steel wire with excellent fatigue strength.
More specifically, the present invention relates to a method for producing a spring steel wire with excellent fatigue strength that can be used in mechanical springs such as internal combustion engine valve springs, clutch springs, and brake springs that require extremely high fatigue strength.

[Prior art] In general, in steels that require high fatigue strength, such as valve springs, fatigue caused by the matrix and nonmetallic inclusions is reduced by increasing the strength of the base material, making nonmetallic inclusions harmless, and hardening the surface layer. It is well known to promote or prevent fractures at high lifetimes. For example, Tokuko Sho 54-00
In Publication No. 7254, in order to render non-metallic inclusions harmless, the inclusions are mainly composed of spesalite, and A L O
It is stated that 3/5iOt+Mn0=0.15 to 0.40. Furthermore, many studies have been proposed regarding increasing the strength of the base material and hardening the surface layer.

However, since the inclusions described in the above publication span the range where corundum is the initial product, it is difficult to prevent the generation of extremely hard and harmful corundum in actual manufacturing, and sufficient No effect is obtained. Furthermore, the degree of processing required to stretch and render the softened inclusions harmless and the characteristics of the wire that can withstand such processing are unclear.

[Problems to be Solved by the Invention] In view of the above-mentioned problems with the conventional method of manufacturing steel that requires high fatigue strength, the present inventor has conducted extensive research and has developed the following: By stretching the softened inclusions well through hot rolling and regulating the area reduction rate to a sufficiently large value or higher through wire drawing, hot rolling that can be finely crushed and dispersed and withstand wire drawing can be achieved. By clarifying the characteristics of the wire and specifying the strength of the final strand to a sufficiently large value, they developed a method for manufacturing spring steel wire with excellent fatigue strength.

[Means for Solving the Problems] The method for manufacturing a spring steel wire with excellent fatigue strength according to the present invention includes: (1) C0.5-0. ht%, S i 0.8-2
．． 5wt%, Mn 0.1-1.0wt%, Cr 0.
1 to 2.0 wt%, the remainder consisting of Fe and unavoidable impurities, ALO 340 wt% or less, S 40235 to 87 wt%
A high-cleanliness steel containing 30 wt% or less of MgO and non-metallic inclusions consisting of the balance CaO, MnO and unavoidable impurities is hot-rolled into a wire rod, and then wire-drawn at an area reduction rate of 70 to 95%. ,
Hardened and tempered to increase strength to 205 kgf/
The first invention provides a method for manufacturing a spring steel wire with excellent fatigue strength characterized by having a tensile strength of 0.5 to 0.8 wt% and a Si of 0.8 to 0.8 wt%.
2.5wt%, Mn 0.1-1. ht%, Cr 0.
Contains L ~ 2.0 wt%, and further contains V 0.03 ~ 0.50 wt%, N (2, Q W t
% or less, Nb 0.03-0.5 (hwt%, Mo 0
．． A120340wt% or less, 540235-87wt%
, Mg0, containing 30 wt% or less, and the remainder containing non-metallic inclusions consisting of CaO, MnO and unavoidable impurities, is hot-rolled into a wire rod, and then wire-drawn with an area reduction rate of 70 to 95%. ,
After quenching and tempering, the strength is increased to 205 kgf/
A second invention provides a method for producing a spring steel wire with excellent fatigue strength, characterized in that the steel wire has a tensile strength of 0.5 to 0.8 wt%, and a Si of 0.8 to 0.8 wt%.
2.5wt%, Mn 0. l~1. ht%, Cr 0.
1 to 2.0 wt%, the balance consists of Fe and unavoidable impurities, and Al2Oh 40 wt% or less, Sin, 35 to 87 wt%
%, MgO 30wt% or less, and the remainder contains non-metallic inclusions consisting of CaO, MnO and unavoidable impurities. After hot rolling the high-cleanliness steel into a wire rod, this wire rod is subjected to treatments such as lead patenting, Tensile strength 125 kgf/mm2 or more, aperture 40
% or more, then wire drawing is performed at an area reduction rate of 70 to 95%, and quenching and tempering is performed to increase the strength to 205 kgf/nun' or more. A third invention provides a method for manufacturing a spring steel wire with excellent fatigue strength, (4) G 0.5-0.8wt%, Si 0.8-0.8wt%
2.5wt%, Mn 0.1-1.0wt%, Cr (
Contains 1.1-2.0 wt%, furthermore, V 0.03-0.50 wt%, Ni 2.0 wt% or less, Nb 0.03-0.50 wt%, Mo 0.03
~0.50 wt% of one or more types, the remainder consisting of Fe and unavoidable impurities, and A I20y of 40 wt% or less, SiO235~
High-cleanliness steel containing 87 wt% or less of MgO and 30 wt% or less of MgO and non-metallic inclusions consisting of the balance CaO, MnO and unavoidable impurities is hot-rolled into a wire rod, and then this wire rod is subjected to treatments such as lead patenting. , tensile strength 125kgf/mm' or more, reduction of area 40%
After being tempered to have the above mechanical properties, the area reduction rate is 7.
A fourth invention provides a method for manufacturing a spring steel wire with excellent fatigue strength, which is characterized in that the wire is drawn by 0 to 95% and then quenched and tempered to have a strength of 205 kgf/mm' or more. This invention consists of four inventions.

The method for manufacturing a spring steel wire with excellent fatigue strength according to the present invention will be described in detail below.

First, in the method for producing a spring steel wire with excellent fatigue strength according to the present invention, the components and component ratios of the steel used will be explained.

C is an effective element for imparting strength to spring steel wire, and if the content is less than 0.5 wt%, sufficient strength cannot be expected, and if the content exceeds 0.8 wt%, C is an element that is effective in imparting strength to spring steel wire. Toughness and ductility deteriorate. Therefore, the C content is 0.5 to 0.8
Let it be wt%.

Si is an element that deoxidizes, improves strength, and also improves resistance to settling. If the content is less than 0.8 wt%, this effect will be small, and if the content is less than 2.5 wt%, If the content is increased, the activity of C will be increased, so the rolled material,
This not only promotes decarburization of the heat-treated material and reduces the surface hardness, which deteriorates the fatigue resistance of the spring, but also becomes a source of AI contamination. This causes the fatigue resistance of the spring to deteriorate. Therefore, the S content is set to 08 to 2.5 wt%.

Mn is an element that prevents the adverse effects of S in steel and is effective in deoxidizing. If the content is less than 0.1 wt%, such an effect cannot be expected, and if the content exceeds L0 wt% During hot rolling, the hardenability increases, and there is a high possibility that the structure becomes bainite or martensitic, which deteriorates toughness and ductility, which impairs ease of manufacture and stability. Therefore, the Mn content is set to 0.1 to 10*t%.

Cr is an element that reduces the activity of C and is effective in preventing decarburization during heat treatment.If the content is less than 0.1 wt%, the above effect will be small, and if the content exceeds 2.0 wt%, the M
As with n, hardenability increases during heat treatment and deteriorates toughness and ductility. Therefore, the Cr content is 0.1 to 2.0w
It is assumed to be t%.

■ is effective in refining crystal grains, improving toughness and ductility, and improving resistance to settling.Furthermore, secondary precipitation strengthening can be achieved during strain relief annealing, quenching, and tempering treatments after spring forming. Therefore, it is an effective element for increasing strength, and if the content is less than 0.03 wt%, this effect will be very small, and if it is contained in excess of more than 0.5 (ht%), it will be difficult to increase the strength during quenching. The melt does not penetrate, and undissolved carbides remain, and when this undissolved residue becomes coarse, toughness and ductility decrease.

Therefore, (1) content is set to 0.03 to 0.50 wt%.

Ni is an element that improves hardenability and fracture toughness,
If the content exceeds 2.0 wt%, the second effect will be saturated (L), and there is a risk of forming a large amount of retained austenite. Therefore, the N1 content is 2,0w
t% or less.

Like V, Nb and Mo are effective elements for precipitation strengthening, and are effective for increasing strength by containing them alone or in combination.If the content is less than 0.03 wt%, this effect is small, and If the content exceeds 0.50 wt%, coarse undissolved carbides will be formed. Therefore,
Nb content is 0.03 to 0.50 wt%, Mo content is 0.
．． 03 to 0.5 ht%.

Next, nonmetallic inclusions in the method of manufacturing a spring steel wire with excellent fatigue strength according to the present invention will be explained.

If a large amount of A I 203 is contained, hard inclusions such as corundum or spinel will be formed, and these hard inclusions will not be crushed even if wire drawing is performed at 70 wt% or more, and the fatigue strength will be reduced. deteriorate. Therefore, the upper limit was set at 4 ht% at which these hard inclusions are not generated. S10. In order to prevent the formation of hard inclusions that are rich in
It is desirable that the content is t% or more.

When Sigh exceeds 87 wt%, hard 5ift-rich inclusions occur, and when Sigh is less than 35 wt%, A I 203,
CaO or MgO-based hard inclusions occur, and
These inclusions, like the corundum and spinel described above, are not crushed even after wire drawing of 70% or more and deteriorate the fatigue strength. Therefore, the 5iOz content is 35 to 87
w j%.

If the MgO content exceeds 30 wt%, Mg
O-based hard inclusions occur and deteriorate fatigue strength. Therefore, the MgO content is set to 30 wt% or less.

In the method of manufacturing a spring steel wire with excellent fatigue strength according to the present invention, the wire drawing reduction rate of the hot rolled material will be explained.

As mentioned above, inclusions that have become soft can be made finer by wire drawing, or if the area reduction rate of wire drawing is less than 70%, the effect of finer inclusions is not sufficient, and if wire drawing is more than 95%, At the area reduction rate, the effect is saturated, and there is also a risk of wire breakage. Therefore, the area reduction rate during wire drawing is 70 to 95.
%.

In addition, the strength has been increased by wire drawing, quenching, and tempering.
If it is less than 0.05 kgf/mm', fatigue failure will occur starting from the matrix due to insufficient strength of the base material for high fatigue strength materials such as valve springs.

Therefore, the strength of the steel wire should be 205 kgf/mm' or more.

Furthermore, in order to stably draw the wire to a reduction in area of 95%, the hot-rolled wire must be heated to a tensile strength of 125 kgf/mm2 or more and an area of 40
It is necessary to refine the mechanical property so that it has a mechanical property of % or more.

[Example] An example of the method for manufacturing a steel wire for springs with excellent fatigue strength according to the present invention will be described.

EXAMPLE In this example, a method for manufacturing a steel wire for a valve spring, which requires extremely high fatigue resistance, will be described.

Table 1 shows the components and component ratios of the test steels and the composition ratios of nonmetallic inclusions.

In Table 1, A1 to A5 are steels used in the method of manufacturing spring steel wires with excellent fatigue strength according to the present invention, and B1 to B
5 is comparative steel.

The wire rods provided were hot rolled at a rolling ratio of 50 or higher after casting.

The rail-rolled materials of AI steel shown in Table 1 were subjected to lead patenting and then wire drawn, and the results are shown in Table 2.

According to Table 2, after proper lead patenting treatment, the tensile strength is 25 kgf/+um2 or more, and the aperture is 4.
It is possible to wire draw up to 95% for wires with 0% or more, but wire drawings that do not satisfy this mechanical property can be wire drawn up to 95%.
Wire drawing can only be performed up to %.

The hot-rolled materials shown in Table 1 were subjected to lead patenting treatment under the patenting conditions shown in Table 2, and all had a tensile strength I of 25 kgf/mm2 or more and a reduction of area of 40%.
After the above, after wire drawing, quenching, tempering, and peening, a test was conducted using a Nakamura rotary bending fatigue tester.

Table 3 shows the results of this test.

From this Table 3, it can be seen that the steel wires manufactured by the method of manufacturing spring steel wires with excellent fatigue strength according to the present invention all achieved lXl07 times in the Nakamura rotary bending fatigue test, whereas the comparative steels All ruptured in less than I X I O' times.

Figure 1 shows the results of measuring the size of inclusions during the wire drawing process for AIM, B1 steel, and B211. While the effect is remarkable, B111,
It can be seen that with B2 steel, it is not possible to achieve a large reduction in area during wire drawing, and furthermore, the effect of increasing the reduction in area to make the inclusions finer is much smaller.

Further, in the steel wire manufactured from B5, since the bow tensile strength is less than 205 kgf/mm2, which is lower than the strength level of the base material itself, fatigue failure occurs starting from the matrix.

In addition, since the steel wire manufactured by the method of manufacturing a spring steel wire with excellent fatigue strength according to the present invention contains V, Nb, and MO, carbides are finely precipitated and ultrafine grains are formed overnight. This makes it possible to manufacture steel wires that can improve the fatigue resistance and heat resistance, which are important for valve spring wires.Furthermore, by incorporating Ni, fracture toughness is improved, making it more resistant to surface flaws, etc. This reduces sensitivity and improves coiling properties.

[Effects of the Invention] As explained above, since the method for manufacturing a spring steel wire with excellent fatigue strength according to the present invention has the above configuration, the manufactured steel wire has a high bow I tensile strength. In addition, by controlling the composition of nonmetallic inclusions and making the inclusions harmless through miniaturization, conventional materials (for example, 5AE9254, etc.)
It is possible to obtain a higher fatigue strength than the previous spring, and it also has the extremely excellent effect of not only making the engine smaller and lighter, but also making it possible to create an internal combustion engine with high output performance with a small spring. It is something.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the area reduction rate during wire drawing and the thickness of nonmetallic inclusions.

Claims (4)

[Claims] (1) C0.5-0.8wt%, Si0.8-2.5w
t%, Mn0.1-1.0wt%, Cr0.1-2.0
wt%, the remainder consists of Fe and unavoidable impurities, and Al_2O_340wt% or less, SiO_235-87
A high-cleanliness steel containing 30 wt% or less of MgO and non-metallic inclusions consisting of the balance CaO, MnO and inevitable impurities is hot rolled into a wire rod, and then wire drawn at an area reduction rate of 70 to 95%. do the
Hardened and tempered to increase strength to 205kgf/mm
A method for producing a spring steel wire with excellent fatigue strength, characterized in that the steel wire has a tensile strength of ^2 or more. (2) C0.5-0.8wt%, Si0.8-2.5w
t%, Mn0.1-1.0wt%, Cr0.1-2.0
further contains V0.03 to 0.50 wt%, Ni 2.0 wt% or less,
Nb0.03-0.50wt%, Mo0.03-0.5
Al_2O_340wt% or less, SiO_235-87
A high-cleanliness steel containing 30 wt% or less of MgO and non-metallic inclusions consisting of the balance CaO, MnO and inevitable impurities is hot rolled into a wire rod, and then wire drawn at an area reduction rate of 70 to 95%. do the
Hardened and tempered to increase strength to 205kgf/mm
A method for producing a spring steel wire with excellent fatigue strength, characterized in that the steel wire has a tensile strength of ^2 or more. (3) C0.5-0.8wt%, Si0.8-2.5w
t%, Mn0.1-1.0wt%, Cr0.1-2.0
wt%, the remainder consists of Fe and unavoidable impurities, and Al_2O_340wt% or less, SiO_235-87
After hot rolling a high-cleanliness steel containing 30 wt% or less of MgO and non-metallic inclusions consisting of the balance CaO, MnO and unavoidable impurities into a wire rod, this wire rod is subjected to treatments such as lead patenting. , tensile strength 125kgf/mm^2 or more, aperture 40
% or more, then wire drawing with an area reduction rate of 70 to 95%, and quenching and tempering to achieve a strength of 205 kgf/mm^2 or more. A manufacturing method for spring steel wire with excellent fatigue strength. (4) C0.5-0.8wt%, Si0.8-2.5w
t%, Mn0.1-1.0wt%, Cr0.1-2.0
further contains V0.03 to 0.50 wt%, Ni 2.0 wt% or less,
Nb0.03-0.50wt%, Mo0.03-0.5
Al_2O_340wt% or less, SiO_235-87
After hot rolling a high-cleanliness steel containing 30 wt% or less of MgO and non-metallic inclusions consisting of the balance CaO, MnO and unavoidable impurities into a wire rod, this wire rod is subjected to treatments such as lead patenting. , tensile strength 125kgf/mm^2 or more, aperture 40
% or more, wire drawing is performed at an area reduction rate of 70 to 95%, and quenching and tempering is performed to increase the strength to 205 kgf/mm^2 or more. A manufacturing method for spring steel wire with excellent fatigue strength.