JPS62274051A - Steel excellent in fatigue resistance and sag resistance and steel wire for valve spring using same - Google Patents

Abstract

PURPOSE:To improve sag resistance as well as fatigue resistance, by subjecting a steel in which the amounts of C, Si, Mn, Cr, Al, V, etc., are specified to oil tempering treatment and by regulating so that tensile strength bears the prescribed relationship with wire diameter. CONSTITUTION:The titled steel has a composition consisting of 0.5-0.8% C, 0.8-2% Si, 0.1-0.7% Mn, 0.5-1.2% Cr, <=0.005% Al, 0.05-0.5% of one or more elements among V, Mo, Nb, and Ta, and the balance Fe. This steel is subjected to oil tempering treatment, by which the relationship between tensile strength and wire diameter is regulated so that T.S=71d<-1/2>+173-71d<-1/2>+203 (where T.S means tensile strength [kgf/mm<2>] and (d) means wire diameter [mm] is satisfied.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a steel with excellent fatigue resistance and fatigue resistance, and a steel wire for valve springs using the same steel. , especially valve springs for internal combustion engines,
It relates to mechanical springs such as clutch springs and brake springs.

[Prior Art] An oil-tempered wire made of Si-Cr steel is used as a typical copper for valve springs, which is required to have fatigue resistance and fatigue resistance.

The tensile strength of these wires is expressed as a rough formula depending on the wire diameter.

T, S = 71d-172+155 (T, S: tensile strength [kgf/mm''] d: strand diameter [mmφ]
) is given by.

Specifically, when calculating the tensile strength based on this formula, it is 4 [m
mφ] wire, T and S are approximately 190 [kgf/mt
It becomes n'l.

Also, 5WRS67B is used as an oil tempered wire for valve springs.
For piano wire, etc. are sometimes used. The tensile strength of the wire at this time is even lower than the oil-tempered wire of 5i-Cr steel, and the target tensile strength for a 4.0 [mmφ] wire is about 165 [kgf/mm''].

Furthermore, as the wire for the valve spring, a wire that has been drawn may be used in some cases.

A typical example is wire drawn from 5WRS82A, which has a tensile strength of approximately 170 k
gf/mm'.

There are the following standards regarding conventional valve spring wires.

<(JIS standards, etc.) JIS G3566, JIS G3561, JIS
G3565. JSMA (Japan Spring Manufacturers Association Standards) [Problems to be solved by the invention] In general, in compression/tension coil springs, the spring height H [mmml] and the twisting that occurs in the bare wires when an axial force is applied. The stress (τ [kgf/mm''l) is given by the following equation.

H=A@Naad・---・・■ τ=8・P −D/π・d3・・・・・・ ■However.

A: Constant, Na: Effective number of turns d: Wire diameter [mm] P: Load applied to spring [kgf] D: Coil average diameter [mm] By the way, by lowering the height of the valve spring, the valve spring Not only that, but also the entire valve drive system and the block protecting it can be made lighter.

Therefore, in order to reduce the height of the spring, it is necessary to reduce the effective number of turns (Na) and the diameter (d) of the strands from equation (2).

However, in this case, there is a contradictory relationship in that the repetitive stress acting on the spring increases from equation 0, and the fatigue life of the spring decreases.

Furthermore, in order to improve the output of an engine, etc., it is most effective to increase the engine speed. Therefore, it is often desirable to increase the natural frequency of springs used in important parts of engines and the like.

In addition, the natural frequency is fl=3.56X10S ad/Na1ID2...
...■ Given by (JIS B2704).

For this purpose, it is necessary to reduce the effective number of turns (Na) and increase the wire diameter (, d) of the spring.

However, increasing the wire diameter (d) is inappropriate for weight reduction, so the effective number of turns (Na
), but in this case as well, the reversing stress acting on the spring increases, resulting in a reciprocal relationship: the fatigue life of the spring decreases.

From the above, in order to guarantee the fatigue life of the spring, it is necessary to improve the strength of the spring material.

Even with 5i-Cr steel, which is the typical material for spring wires currently in use, high-strength wires can be obtained by lowering the tempering temperature during oil tempering.
In this case, the following problems arise.

Tempering treatment is carried out using molten lead, but in order to increase the strength of current Si-Cr steel, it is necessary to heat the molten lead to 4 mm using a wire with an strand diameter of 4-0 [mmφ].
However, the melting point of molten lead is 327°C, and at this processing temperature, lead will adhere to the surface of the treated steel wire.

Furthermore, if the tensile strength is 220 [kgf/mm''] or more, the ductility will be extremely reduced, leading to breakage during spring coiling and a shortened fatigue life.

Generally, formed springs are subjected to bluing treatment to remove strain during spring forming and to improve the elastic limit, but in order to maintain high strength with current 5i-Cr steel, the bluing temperature must be low. Therefore, sufficient effects cannot be obtained regarding the above-mentioned problems.

Therefore, the present invention was created with the aim of providing a steel that has high ductility even at high strength and maintains its strength even at high bluing treatment temperatures.

[Means for solving problems] The present invention consists of the following two inventions.

In the first invention, the chemical components are 0.5 to 0.0% by weight.
8%, Si: 0.8-2.0%, Mn: 0, 1
~0, 7%, Cr: 0.5-1°2%, Al: 0.0
The present invention relates to a steel having excellent fatigue resistance and set resistance, in which one or more of V, Mo, Nb, and Ta is added in an amount of 0.05 to 0.5%, and the balance is Fe.

In the second invention, the steel of the first invention is subjected to oil tempering treatment, and the tensile strength is 71 d -172+ with respect to the wire diameter.
173≦T, S<71d-1/2+20:](T
, S: Tensile strength [kg f / m] d: Wire diameter [
This relates to a steel wire for a valve spring that is adjusted to have the following relationship:

[Operation] The reason for limiting the chemical composition of the steel of the first invention will be explained.

C: C is an effective element for increasing strength, but 0.
If it is less than 5%, sufficient strength cannot be obtained;
If it exceeds 0.8%, toughness will deteriorate. Therefore, the amount of C is (
The content was set at 15% to 0.8%.

Si: Si is an element that is effective in deoxidizing and greatly contributes to strength when oil tempered, and if it is less than 0.8%, it is difficult to achieve high strength. On the other hand, if it exceeds 2.0%, it not only promotes decarburization and reduces the surface strength, but also
This is a source of A1 contamination. As will be described later, an increase in AI causes the formation of non-ductile inclusions, which deteriorates the fatigue properties of the spring. Therefore, the amount of Si was set to 0.8 to 2.0%.

Mn: In the quenching and tempering process, the hardenability of the steel is important, and for this purpose Mn must be added.
It is necessary to add a certain amount of Mn to play the role of fixing S, which is harmful to the toughness and ductility of steel. However, if it is added too much, the ductility of the treated steel decreases, making it impossible to obtain a high-strength wire. Therefore, the amount of Mn was set to 0.1 to 0.7%.

(See Figure 1) ■: The addition of ■ makes the grains finer and contributes to improving the toughness and ductility of the treated steel. It is also effective in improving resistance to settling. Furthermore, (2) secondary precipitation strengthening is achieved in strain relief annealing and oil tempering treatment after spring forming, which increases tempering softening resistance and is effective in increasing strength. However, 0゜0
Below 5%, the effect becomes very small.

(See Figure 2) On the other hand, if too much ■ is added during austenitization in oil tempering, it will not dissolve and undissolved carbides will remain in the oil tempered material, and if these undissolved carbides become coarse, the ductility of the treated material will increase. decreases. Therefore, there is an upper limit to this amount of addition, which is 0.5%.

Based on the above, the amount (1) was set to 0.05 to 0.5%.

A I = A large number of materials containing 0.005% or more of AI (7) A
1203 is produced.Al 203 is not only non-ductile, but also very hard, leading to premature failure in fatigue tests. For this reason, the amount of AI added should be suppressed as much as possible, and should be less than 0.00%.

Mo, Nb, Ta: These are elements that impart precipitation strengthening like (2), and are effective in increasing strength when added alone or in combination. However, the effect is small below 0.05%.

If it exceeds 0.5%, coarse undissolved carbides will form, so 0.
．． 05 to 0.5%.

Next, the reason for limiting the tensile strength of the second invention will be explained.

Generally, the fatigue limit of a spring wire increases as the tensile strength of the wire increases.

However, the tensile strength is T, S = 7fd-12+15
Even if the strength is about 10 [kgf/mm'l larger than the strength given by
If the strength is greater than that given by 3, the toughness and ductility will be insufficient,
Not only does breakage increase during coiling, but the fatigue limit also decreases.Therefore, the above-mentioned steel is treated with oil tempering,
Tensile strength versus strand diameter: 71d l/2+ 173≦T, S≦71d-1/2+
A steel wire for a valve spring was obtained by adjusting the relationship to have a relationship of 203.

[Example] Using the test steels (a-f) shown in Table 1, the strand diameter was 4.2[
mmφ] wire was manufactured, oil-tempered, and then tested using a Nakamura rotary bending fatigue tester to determine the fatigue limit.

The results are shown in Table 2, and the invention steels a, b
shows excellent fatigue properties even at high strength, but comparative steel c
, d, when the strength is increased, the fatigue properties worsen. Note that it is difficult to make comparative steels e and f high in strength.

Also, for steel types a and e, the spring constant is 2゜5 [kgf/
mm] of the coil spring, and the tensile strength of the wire is 1
Setting was performed with a stress of 72, and the test stress was 80 [kg
Apply a constant load to 24 [hrl,
The residual shear strain was measured at tso°C.

The results are shown in Table 3, and the invention steel a has a comparative tR
It can be seen that even if the tensile strength is the same as e, there is little sagging, but by increasing the strength, the sagging resistance is further improved.

[Effect of the invention 1 By using the steel of the present invention, the conventional 5t-Cr
By processing at tempering and bluing temperatures similar to steel, T,5 = 71d-1/2 +173
Not only can an oil tempered wire with a tensile strength of 1 kgf/mm'' or more be obtained, but also a steel wire with ultrafine grains can be produced.

Also, by using this wire.

It is possible to obtain a steel wire for valve springs that has higher fatigue strength than conventional steel wires, and since the steel of the present invention suppresses AI to an extremely low level, non-ductile inclusions that are harmful to fatigue are also extremely reduced. be able to.

Therefore, it is possible to obtain higher fatigue strength than conventional materials (Si-Cr steel, etc.), which not only contributes to the miniaturization and weight reduction of engines, but also allows internal combustion engines to have high output functions with small springs. It becomes possible to give.

In addition, by adding (■), vanadium carbide is finely precipitated in the oil-tempered wire, and it is possible to manufacture steel wire with ultra-fine grains as described above, which improves the resistance to fatigue, which is important in steel wire for valve springs. It also improves properties and heat resistance.

Table 2 (Kgf/+m2) Table 3

[Brief explanation of the drawing]

Figure 1 is a graph showing the reasons for limiting the upper limit of Mn content, with the horizontal axis representing the Mn content and the vertical axis representing the tensile strength. Figure 2 is a graph showing the reason for limiting the upper limit of Mn content. This is a graph showing the relationship between bluing temperature and tensile strength with the content of ■ being taken as a parameter. Mn content (wt muscle Figure 2 tensile strength kgf/mm') Blueing temperature ('0) Procedural amendment 1, case description 1986 Patent Application No. 118207 2, name of invention Fatigue resistance, resistance to Steel wire with excellent flexibility and steel wire for valve springs using tuning 3, and its relationship to the amended case Patent applicant address 1-3-18 Wakihama-cho, Chuo-ku, Kobe-shi, Hyogo Name (119) Kobe Steel, Ltd. Representative: Fuyuhiko Maki 4, Agent: 160 Telephone: 03 (358) 8840
Address: 12-6, Honshio-cho, Shinjuku-ku, Tokyo, Number of inventions increased due to amendment: 07,
Claims column and Detailed Description of the Invention column 8 of the specification to be amended, contents of the amendment (1) The claims of the specification will be amended as shown in the attached sheet. (2) Between the third and fourth lines of page 10 of the specification, r
Cr: Cr is an effective element for preventing decarburization, and is also effective for increasing the strength of steel because it increases resistance to tempering and softening. If it is less than 0.5%, the effect is small, 1.2%
Since toughness deteriorates when the content exceeds 0.5% to 1.2%. ” Insert. Claims (1) Chemical components in weight%: C: 0.5-0.8% Si: 0.8-2.0% M n + 0, 1-0, 7% Cr: 0.5 ~1.2% A1: 0.005% or less, 0.05% of one or more of V, Mo, Nb, Ta
A steel with excellent fatigue resistance and sag resistance, characterized in that ~0.5% is added and the balance is Fe. (2) Chemical components in weight%: C: 0.5-0.8% Si: 0.8-2.0% Mn: 0, 1-0, 7% Cr: 0, 5-1, 2 % Al: 0.005% or less, one or more of V, Mo, Nb, Ta is 0
．． 05 to 0.5%, the remainder being Fe, was oil tempered, and the tensile strength was determined relative to the wire diameter. 71d-1/2+ 173≦T, S≦71 d-1/
2 + 203 (T, S: tensile strength [k g'f /
A steel wire for a valve spring, characterized in that the steel wire is adjusted to have the following relationship: mm']d: strand diameter [mm].

Claims (2)

[Claims] (1) Chemical components in weight%: C: 0.5-0.8% Si: 0.8-2.0% Mn: 0.1-0.7% Cr: 0.5-2.0% Al: 0.005% or less, one or more of V, Mo, Nb, Ta at 0.05% or less
A steel with excellent fatigue resistance and sag resistance, characterized in that ~0.5% is added and the balance is Fe. (2) Chemical components in weight%: C: 0.5-0.8% Si: 0.8-2.0% Mn: 0.1-0.7% Cr: 0.5-1.2% Al: 0.005% or less, and 0.005% or less of one or more of V, Mo, Nb, and Ta.
05 to 0.5%, the balance being Fe is oil tempered, and the tensile strength is determined to be 71d^-^1^/^2+173≦T. S≦71d^-
^1^/^2+203 (T.S: tensile strength [kgf/m
m^2] d: Wire diameter [mm]) A steel wire for a valve spring, characterized in that it is adjusted to have the following relationship.