JPS5827958A - Spring steel with superior yielding resistance - Google Patents

Abstract

PURPOSE:To obtain a spring steel with superior yielding resistance by adding a specified percentage each of C, Si, Mn, W and Ta to Fe. CONSTITUTION:A steel consisting of, by weight, 0.50-0.80% C, 1.50-2.50% Si, 0.50-1.50% Mn, 0.05-1.00% W and/or 0.05-0.50% Ta, and the balance essentially Fe is prepared. To the steel may be added 1 or >=2 kinds among 0.05- 0.50% V, 0.05-0.50% Nb and 0.05-0.50% Mo, and/or 1 or >=2 kinds among 0.03-0.10% Al, 0.02-0.10% Ti and 0.02-0.10% Zr. A spring steel superior to SUP7 in yielding resistance and equal to SUP7 in fatigue resistance and toughness is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spring steel with excellent fatigue resistance.

Conventionally, 5UP6. SUPg was the main thing. In recent years, there has been a demand for lighter automobiles, and there has also been a strong demand for lighter suspension systems themselves.

In response to this, various measures have been attempted for suspension systems in general, but among these measures, a measure of increasing the design stress of the spring is considered to be effective. In this way, high stress setting a1
Accordingly, when a spring is manufactured using the above-mentioned conventional spring material, a problem arises in that the sag increases. In particular, when used in passenger cars, it has been found that an increase in fatigue is linked to a decrease in bumper height.As a result, it has been discovered that increasing the 8+ content in spring steel improves fatigue resistance.Recently, S It has a higher St content than TJ P 6 and 1. SUP 7, which has the highest SI among the steels for springs specified in s I S G 4 s o t, has come to be widely used as copper for suspension springs of passenger cars.

However, there are strict requirements for reducing the weight of suspension springs, and there has been a strong desire to develop copper for springs that is even more resistant to fatigue than 5UP7.

(3) Against this background, the present invention was developed as a result of repeated research by the present inventors, and was developed by adding an appropriate amount of W to high-Si spring copper.

One or two types of Ta or further Ar.

STJ IF 7 by adding one or more types of Nl), Mo, or one or more types of A, l, T + r Z r
, J: Rimo has developed copper for springs that has excellent fatigue resistance and also has the same performance as SUP 7 in terms of fatigue resistance and toughness required for copper for springs.

W, 'l''a, V, N11.Mo form carbides in steel, and these alloy carbides dissolve into austenite during heating during quenching. When this is rapidly cooled and quenched, these elements become supersaturated. Solid solution martensite is obtained. When this is tempered, fine alloy carbides begin to re-precipitate in the process, which prevents the movement of dislocations in the steel and causes secondary hardening, resulting in W, Ta, and V.
Nl) has the effect of increasing hardness compared to spring copper without the addition of Mo and further improving resistance to settling.

In addition, A, l, T 1 + Z r often combine with (4) and N in steel to form alloy nitrides, thereby refining austenite crystal grains and preventing their coarsening. The crystal grains refined in this manner improve the resistance to settling by reducing the amount of movement of dislocations.

In addition, as mentioned above, secondary hardening means that when aiming for the same tempering hardness range, the tempering temperature range can be wider than that of conventional steel.
This means that the desired hardness can be stably obtained. In order to clarify this further, A1 steel containing 0.81% W, A2 steel containing 0.31% Ta, which will be described later,
A3 steel containing 0.45% W and 0.20% (7) Ta and SUP7 Bl steel were heated to 300 to 65%.
Figure 1 shows the results of tempering at 0°C and measuring the hardness. A1 containing W and Ta appropriately
As is clear from Figure 1, the steel of the present invention, 83 steel, has a wider tempering temperature range corresponding to hardness than the conventional steel, and at the same time shows an increase in hardness indicating the occurrence of secondary hardening. is observed at a tempering temperature of 550°C.

ρ, ρ2/ ρ・′ノA8 steel, 0.59% W and ← Valve → % Al and Ho ＃幡% 0
) Addition of Ti A, 9 steel, 0.25% No'I
'a, Q.

0yo8% Al, 0.06%(1) Ti added: A10 steel, 0.22% Ta and 0.067%0
') A, (Jfx addition, ?, = 5 for A11 steel and conventional steel
Figure 2 shows the results of measuring the austenite grain size using the oxidation method on UP7 Bl steel. As is clear from Fig. 2, Al, Ti, which are elements for refining crystal grains,
It can be seen that by adding , the crystal grains become finer by about 3 in terms of grain size number compared to the conventional steel 5UP7.

The chemical structure of the steel of the present invention is C! 0. ．． 50-0.80%
.

Si 1.50~2.50%, Mn 0.50~
Contains 1.50%, and further contains wo, o5~1.0%,'
Contains one or two of 0.05 to 0.50% of I'a, and has a content of 5 to 0.0% depending on the purpose of use.
50%, Nl) 0°05~0.50%, Mo 0
．． One or more of 05 to 0.50%, or further A10.03 to 0.10%, Ti 0
．． 02 to 0.10%, Zr□, and 02 to 0.10%, and the remainder substantially consists of Fc.

The reasons for limiting the composition of the steel of the present invention will be explained below.

The reason for setting the C content to 0.50 to 0.80% is because if it is less than 0.50%, sufficient strength cannot be obtained as copper for high stress springs by quenching and tempering. This is because, if it is, it becomes a hypereutectoid steel and the toughness decreases significantly.

The S+ amount is 1.50-250%, which means 150%.
In the following cases, the effect of increasing the strength of the base material and improving the sagging resistance by solid solution in the ferrite possessed by Sl cannot be sufficiently obtained, and even if the content exceeds 250%, the sagging resistance will not increase. This is because the effect of improving properties may reach saturation and free carbon may be generated due to heat treatment.

The amount of M and n is 0.50 to 1. ．． 50% is 05
This is because if the content is less than 0%, the strength as copper for springs is insufficient, and furthermore, the hardenability is insufficient, and if the content exceeds 1.50%, the toughness is inhibited.

+71 W, Ta, V, Nb, Mo i, and t are all elements that improve the sag resistance in the steel of the present invention.

1゛a, Ar, Nb, which play such a function
M.

The content of W is 0.05 to 0.50%, and the content of W is 0.
The reason why it is set at 0.05% to 1.00% is that the above effect cannot be obtained sufficiently below 0.05%, and Ta, V, and Nb
, 0.50% for Mo, 1.00 for W
Even if the content exceeds %, the effect is saturated, and the amount of alloy carbide that is not dissolved in austenite increases, forming large lumps that act like nonmetallic inclusions and reduce the fatigue strength of steel. This is because there is a risk of causing
- these W, 'l'', a and V, Nl),
In addition to adding each Mo c'c individually, by adding two or three kinds in combination, dissolution into austenite starts at a lower temperature than when adding them alone, In addition, the precipitation of fine alloy carbides during the tempering process promotes secondary hardening.
: This further improves the fatigue resistance.

(8) Also, A which improves the resistance to settling by making the crystal grains finer.
The content of l o + p l + Z r is 0.03-0.10% for Ae, and 0 for T1 and Zr.
．． The reason why the content is 0.02 to 0.10% is that if the content is less than 0.02%, the distribution of these nitrides will be sparse and will not contribute to grain refinement.If the content exceeds 0.10%, cracks will occur during hot rolling. This is because there is a possibility that the toughness of the steel may be deteriorated as non-metallic inclusions.

Next, the characteristics of the steel of the present invention will be clarified through examples in comparison with conventional steel.

Table 1 shows the chemical composition of these test steels.

Table 1 All of these samples were hot rolled at a rolling ratio of 50 or more after casting, but were tested.

In order to examine the fatigue resistance properties of the present invention 1, a coil spring having the specifications shown in Table 2 was prepared using the above-mentioned test steel and quenched to give a final hardness of c45 to c55.・After tempering, the shear stress of the wire is 1], 1.5
A set test piece was prepared by setting the weight to 1 kg/-. This test piece was then held at a constant temperature of 20°C.
A load such that the shear stress of the wire is τ = 1.05 klj/- is applied for 96 hours (hereinafter referred to as long-term load)
The fatigue of the coil spring was measured after

Table 2 The amount of set in relation to the hardness of the above test piece is shown in Table 3 to 6.
Shown in the figure. As is clear from FIGS. 3 to 6, W and Ta are substantially present in STJ P7, which is the steel of the present invention.

A1-A3 steel (Fig. 3) S with one or two added
A4 to A7 steel (Fig. 4), STJ, in which one or two of W, IIIa and one or more of V, Nl+, and Mo are added to TJ P7 (Fig. 4).
]W to F7.

One or two types of Ta are added, and further Al and T;.

A8 to A11 steels containing one or more of Zr (Fig. 5), 5UP7 with one or more of W and Ta (further V, Nl), one or more of MO,
Furthermore, steels A, 12 to A, and 15 (Fig. 6) to which one or more of Kl, Ti, and Zr were added had a higher concentration compared to B1 steel, which is a conventional steel and is essentially SU and P. It is recognized that the invented steel has excellent resistance to settling.

In addition, among the steels of the present invention, W and T, which are precipitation-strengthening elements, are
Steels that have a combination of a, , V, N1+, etc. added, as well as grain refinement elements such as AI and Ti, have better resistance to settling than those that have them added alone. It can be seen that it has.

The amount of settling is determined by the load P1 required to compress the coil spring to a certain height before applying the long-term load, and the load P2 required to compress the coil spring to the same height after applying the long-term load. Measure the difference △P (=P1-P2)
J: Calculated using the following equation, and has a unit of shear strain, and was evaluated using a value called residual shear strain.

γR-Up・K-fiu△P G π (18 G; Transverse elastic modulus (kQf/mrM) D As a result of repeated fatigue tests using the same shape, none of the coil springs broke even after 200,000 cycles.

As mentioned above, the steel of the present invention is made by adding appropriate amounts of W and Ta, singly or in combination, to conventional high-Si spring copper, and further adding V and N.
l), by adding Mo alone or in combination, or by adding A I + T + r Zr alone or in combination, the excellent fatigue resistance of conventional high St copper for springs can be improved. We have succeeded in further improving the fatigue resistance required for copper for springs.
Its toughness is also comparable to that of conventional steel, and it has extremely high practicality, especially as copper for suspension springs for passenger cars.

[Brief explanation of the drawing]

Figure 1 shows the steel of the present invention and the conventional steel after being quenched.
Diagrams showing the results of tempering at 650°C and measuring the austenite grain size at the hardening temperature using an oxidation method. It is a diagram showing the amount of settling of a test piece with a hardness of T (&C 45 to 55) after restoration treatment. !lv Bunsho 58-27958 (5)

Claims (1)

[Claims] 1 CO, 50-0.80% by weight, Flil
. 50-2.50%, M, n O, 50-1. ．． 5
0% and WO, 05~1.00%, 'I''' 0
．． 1. A spring steel having excellent fatigue resistance, characterized in that it contains one or two of Fc in an amount of 0.05 to 0.50%, and the remainder substantially consists of Fc. 2 Weight ratio (30,50-0.80%, Sin. 50-2.50%, M, n 0.50-1.50%
and WO, 05~1.00%, Ta O, 05~
Contains one or two of 0.50%, and further contains Vo
, 05-0.50%, NbO, 05-0.50%, MO
1. A spring steel having excellent fatigue resistance, characterized in that it contains one or more of the following: 3 00.50-080% by weight, Sil. 50-2.50%, M, no, 5'O-1. ．．
50%, Wo, 05-1.00%, Ta 0.
Contains 0.05-0.50% of one or two types of Nochi, and further contains A [0.03-0.10%, Ti 0.02-0
．． 10%, ZrQ, and one or more of 92 to 0.10%, with the remainder substantially consisting of Fc. 4 CO, 50-0.80% by weight, 8 tl. 50-2.50%, Mno, Ri 0-1.50%
and WO, 05~1.00%, Ta 0.05~
One or two of 0.50% and V 0.05-0
．． 50%, Nb0105~0.50%, MOo, 05~
One or more of 0.50%, and further Al,
0.03-0.10%, Ti 0102-0.10%,
A spring steel having excellent resistance to setting, characterized in that it contains one or more of 0.02 to 0.10% of Zr, and the remainder substantially consists of Fe.