JPS5827960A - Spring steel with superior yielding resistance - Google Patents

Abstract

PURPOSE:To obtain a spring steel with superior yielding resistance and hardenability by adding a specified percentage each of C, Si, Mn, V, Nb, Mo, etc. to Fe. CONSTITUTION:A steel consisting of, by weight, 0.50-0.80% C, 1.50-2.50% Si, 0.50-1.50% Mn, 1 or >=2 kinds of elements selected from 0.05-0.50% V, 0.05- 0.50% Nb and 0.05-0.50% Mo, 1 or >=2 kinds among 0.20-2.00% Cu, 0.05- 1.00% Co and 0.01-2.00% Be, and the balance essentially Fe is prepared. To the steel may be added 1 or >=2 kinds among 0.03-0.10% Al, 0.02-0.10% Ti and 0.02-0.10Zr, 1 or >=2 kinds among 0.0005-0.0100% B, 0.20-1.00% Cr, 0.20- 2.00%Ni and <=0.30% rare earth element, or 0.05-1.00% W and/or 0.05-0.50% Ta.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to copper for springs with excellent stiffness.

Conventionally, various methods have been tried for springs used in suspension systems for automobiles and other suspension systems in general, but among these, a method for increasing the stress in the spring is considered to be effective. Along with this high stress design, when springs were manufactured using the conventional copper material for springs described in item 1, a problem occurred in that the set-off increased. Particularly when used in passenger cars, an increase in stiffness leads to a decrease in bumper height, which poses a major safety problem. As a result of various studies, it was discovered that increasing the St content in spring steel improves the resistance to sagging. 1. Among the spring steels specified in TIS G 4.801, S rJ P 7, which has the highest steel of 81, has come to be widely used as a copper for passenger car suspension springs.

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 SUP7.

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 ■ to copper for high 81 springs.

Nb, A4. Adding one or more types of 'o',
Furthermore, in addition to adding one or more types of Co, On, and BO, depending on the date of use, A, g,
Ti.

One or more of Zr, B, Cr, and Ni.

By adding one or more rare earth elements and one or two of W and Ta, STJ P 7
It has better fatigue resistance and hardenability than S TJ P7, and also has the fatigue resistance and toughness required for spring copper.
We have developed copper for springs that has performance equivalent to that of springs.

V, N'b, Mo, W, and Ta each form a carbide in the steel, and these alloy carbides dissolve in the austenite during heating during quenching. When this is rapidly cooled and quenched, martensite containing these elements in a supersaturated solid solution is obtained. When this is tempered, fine alloy carbides begin to re-precipitate during the process, which blocks the movement of dislocations in the steel and causes secondary hardening, resulting in V, Nb, M
Additionally, alloy carbides that are not dissolved in austenite I during heating during quenching can refine the austenite crystal grains and prevent them from becoming coarser. Moreover, such fine crystal grains improve the resistance to settling by reducing the amount of movement of dislocations.

Further, Co 2 , Co 2 , and Bc form a solid solution in the steel in a substitutional manner similar to St 2 , impart solid solution strengthening to the steel, and improve the sag resistance of the steel.

On the other hand, AI, Ti, and Zr often combine with N in steel to form nitrides, which has the effect of refining austenite grains and preventing their coarsening, thereby reducing the amount of dislocation movement. By reducing this, it contributes to improving the fatigue resistance of the steel.

Also, 11. Or, Ni, and rare earth elements are elements that improve the hardenability of steel, and the additive elements can improve the fatigue resistance even for large and thick springs that require particularly high hardenability. When aiming for a hardness range in a steel, it is possible to set the tempering temperature range to a wider range than with conventional steel, and the desired hardness can be stably obtained. In order to clarify this further, we used Shiri A 15fi, 0.21 * (7
)V, 0.1.2*(7)N'), 0°20
% Ta and further contained 1.30% ELL.
16 steel and S TJ P '7 BI steel from 300~
Figure 1 shows the results of tempering at 650°C and measuring the hardness. As is clear from Fig. 1, the tempering temperature range corresponding to the hardness of the A15+A16 steel of the present invention, which contains precipitation-strengthening elements V, Nb, Ta, and CII appropriately, is lower than that of conventional steel. At the same time, an increase in hardness indicating the occurrence of secondary hardening can be seen at a tempering temperature of 550°C.

Next, regarding the grain refinement effect, 021% Nov,
1. ．． 31% NocIl, O,0y-8% (D
A7 steel with total Al content, 0.19% V, 0.12%
Nb, ].

A9 steel containing ＼ Ti, 0.20% V, 0.14
Results of measuring the austenite grain size at each austenitizing temperature of A10 @ containing % Nb, 0.68% 00, and 0.05% Ti and B1 steel, which is the conventional steel 8UP7, by an oxidation method. is shown in Figure 2.

Looking at FIG. 2, it can be seen that due to the addition of AI or Ti (7), the austeti l-crystal grain size is about 3 finer in terms of grain size number than that of conventional steel.

Moreover, FIG. 3 shows 0.25% V and 1.30% Cu.

All steel containing o, ooao% B, 0.23% v, o,io% Nb, 1.27% Cu,
Q, Q A, 12 steel, 02 containing 21% B
■7%.

A1B steel containing 1.34% C11, 0.62% (7) Or, 0.21. %(7)V, 0.1
5% (7) NIJ, 1.29% The chemical composition of the invention steel is co, 5o ~ 0.80%, Stl, 50 ~ 2.5
0%, Mn 0.50-1.50%, and ■005-0.50%, NlI Q, Q 5-05
0%, MOo, 05 to 0.50%, and further contains C110, 20 to 3.00%.

COO, 05~1.00%, Be-Q, 91~2.0
0%, and further contains A40.0% depending on the usage. O-kai~0.10%, Ti 0002
~010%, Zr 0802 ~ 1 out of 0.10%
Seeds or two or more seeds, or BO, 0O05 to 0.0
100%, Or 0.20-1.00%, Ni
O, 20~2.00%, one or more of rare earth elements 030% or less, or WO105~1.00
%, Ta or 0.05 to 0.50%, and the remainder substantially consists of pe.

- This is because sufficient strength cannot be obtained by closing, and 0.80
This is because if the content exceeds %, the steel will become hypereutectoid and the toughness will be significantly lowered.

The reason why the amount of Si is set to 1.50 to 250% is because if it is less than 1.50%, the effect of increasing the strength of the base material and improving the resistance to settling by forming a solid solution in the ferrite possessed by Si is sufficient. This is because, even if the content exceeds 2.50%, the effect of improving the settling resistance will be saturated, and there is a risk that free carbon will be produced by heat treatment.

The reason why the Mn amount is set to 050 to 150% is because if it is less than 0.50%, the strength as copper for springs is insufficient and also the hardenability is insufficient. This is because if it is contained, the toughness will be impaired.

V, Nll, and Mo are all elements that improve the sag resistance in the steel of the present invention.

However, even if the content exceeds 0.50%, the effect will be saturated, and the amount of alloy carbides that will not be dissolved in the austenite will increase, forming large lumps that will cause the steel to deteriorate due to the action of non-metallic inclusions. This is because there is a risk of reducing fatigue strength.

These V, Nl), and Mo can be added individually or by adding two or three types in combination.
, Nl), M, and o are added alone to the ratio of
Start dissolving into austenite at a lower temperature,
In addition, precipitation of fine alloy carbides during the tempering process
There is a substance-C which further improves the wear resistance by further accelerating secondary curing.

In addition, Cu, Go, and Be are elements that form a solid solution in the steel in a substitutional manner to strengthen the steel and improve its resistance to settling. The content of el+ was set to 0.20 to 300% because
This is because if the content is less than 0.20%, the effect is solid solution strengthening; if it is less than 0.05%, the effect is insufficient, and if it exceeds 1.00%, the toughness may deteriorate.

Similarly, when the Be content was set to 0.01 to 200%,
Although Be is an element with a large solid solution strengthening ability, the above effect cannot be obtained if it is less than 0.01%, and even if it is contained in excess of 2.00%, the effect is saturated as in the case of Sl. be.

In addition, the contents of kl, 'I''l, and Zr, which refine the crystal grains and improve the resistance to settling, were determined for Aβ (11
) is 0.03-0.1.0%, and 0 for Ti and Zr.
The reason why F is set at 0.02 to 0.10% is because the distribution of these nitrides becomes sparse and the crystal grains do not become finer if the F content exceeds 0.10%.
This is because the effect described in item 1-1 is saturated and there is a risk that the hot rolling properties may be inhibited and the toughness of the steel may be deteriorated as non-metallic inclusions.

In addition, B, Or, Ni, and rare earth elements improve hardening and hardening properties, and during hardening, large and thick springs can be removed.
．． 0005 to 0.01.00% is 0°000
This is because if the content is less than 5%, no improvement in hardenability can be expected, and if the content exceeds 0.01.00%, the effect will be saturated. The reason why the Cr content is set to 0.20 to 1.00% is because the effect of improving hardenability is not sufficient if it is less than 0.20%, and if it exceeds 1.00%, This is because the effect on the propensity is almost saturated, and in (12) steel containing a large amount of St like the steel of the present invention, the tempered structure may become non-uniform.

In addition, the reason why the Ni content is set to 0.20 to 2.00% is because if it is less than 0.20%, sufficient quenching property 1 effect cannot be obtained, so if it is contained more than 200%, The effect is saturated, and there is a large amount of residual Ausnai! This is because there is a risk of forming. Similarly, the reason why the amount of rare earth elements is set to 0.30% or less is that if it is contained more than that, the crystal grains may become coarse.

The reason why the content of W, which is an element that imparts precipitation strengthening to steel, is set at 0.05% to 1.00% is that if it is less than 0.05%, the amount of precipitation is insufficient.1. ．． This is because the effect is saturated even if the content exceeds 00%.

In addition, the Ta content was set to 0°05 to 0.50% because
If the content is less than 0.005%, the amount of precipitation will be insufficient as in the case of W, and even if the content exceeds 0.50%, the effect will be saturated, and the undissolved carbides will act as nonmetallic inclusions, causing the steel to deteriorate. This is because there is a risk of deteriorating toughness.

In this case as well, in addition to adding W and Ta alone, 2
By adding seeds in combination, the already added V,
It exhibits a synergistic effect with Nh and Mo to start dissolving alloy carbides at a lower austenitizing temperature and further promote secondary hardening.

Next, the characteristics of the steel of the present invention will be compared with the conventional steel. In Table 1, A1-A16 steel is the steel of the present invention, and Bl steel is the conventional steel, SI-P7. All of these are cast after casting.
A test material was prepared by hot rolling at a rolling ratio of 50 or more.

Then, a coil spring having the specifications shown in Table 2 was formed using the above-mentioned test steel as a raw material, and the final hardness was I:I n, c45.
After quenching and tempering so that the wire had a shear stress of ~55, setting was applied so that the shear stress of the strand was τ-11-5k'j/ynlr to prepare a fatigue test piece.) After 96 hours. (Hereinafter, this is referred to as long-term loading) The coil spring's fatigue claw was measured.

Table 2 However, for A11 to A1.4 steels in consideration of hardenability, test pieces were formed into 1-yon bars with a diameter of φ3 Q mm shown in Table 3, and τ-1101KII'/- After setting, a stress of τ-100 kqr/mrJ was applied, and the amount of settling after being left for 96 hours was determined.

Table 3: Table 3.
It is shown in Figure 7.

As is clear from Figs. 4 to 7, A1-A, which is the steel of the present invention,
It is recognized that all of the No. 16 steels have superior fatigue resistance compared to the conventional steel, B1 steel.

The amount of setback is determined by measuring 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. and the difference △J) (-p,
l) 2) It was calculated using the following formula, and has the unit of shear strain, and was evaluated using a value called residual shear strain.

18I) γ1 (・-mutual・K] △I゛G; transversality rate (k nails/mA) D; ml coil center diameter (ynm) (l; strand diameter (zyy) K; whirl correction coefficient (coil (a constant determined by the shape of the spring) t, AIl ~ A The amount of settling from the 1-version bar conducted on 1.4 steel is the amount of decrease in the torsion angle △θ (r
a, rl) to the amount of residual shear strain according to Yr-Δθ·(J/21).

(l; wire diameter (agony) l; effective length mm) In addition, regarding the present invention steel and conventional steel, A1-A10 steel, A
For 15~A i 6 steel and BL steel, use the above-mentioned coil spring, and for fz~A 1-4 steel, use the above 1・-
Using John Barr, 1o-110':jf/mA
When a fatigue test was conducted under the following conditions, no precipitation occurred even after repeated 200,000 times.

As mentioned above, the steel of the present invention is made by adding appropriate amounts of V, Nb, and Mo to the conventional copper for high 81 springs.
Furthermore, in addition to adding appropriate amounts of Cu, C(+, and Bc, either singly or in combination, an appropriate amount of A is added depending on the purpose of use.
Adding I + TirZr alone or in combination, or adding an appropriate amount of B, Or, Ni, rare earth elements, singly or in combination, or adding an appropriate amount of B, Or, Ni, rare earth element, or
The fatigue resistance and toughness necessary for copper for springs are comparable to those of conventional steels by adding 100% of WrTa either alone or in combination, making it extremely practical as copper for suspension springs for passenger cars in particular. It is something that has a nature.

[Brief explanation of the drawing]

Figure 1 shows the steel of the present invention and the conventional steel after being quenched at 300°C.
Fig. 2 is a diagram showing the hardness of steel tempered at temperatures between ~650℃ and 650℃. Figure 3 is a diagram showing the obtained results, and Figure 4 is a diagram comparing the hardenability of the invention steel and conventional steel.
FIG. 7 is a diagram showing the amount of sag of coil spring test pieces when the hardness after quenching and tempering is T'IR, 045 to 55 for the steel of the present invention and the conventional steel. 36 3rd quenching r 81 Distance from end (1X6i/now)

Claims (1)

[Claims] 1 00.50 to 080% by weight, 8+1
．． . 50-250%, M, n O, 50-1.50%, ■005-050%, Nll Q, Q 5-050
%1M0005 to 050%, and further contains CoQ, 20 to 3.00%, and CoQ. 05-1.00%, BeO, 1 out of 01-2.00%
Copper for springs with excellent fatigue resistance, containing one or more species, and the remainder substantially consisting of p(!). .50%, Mn 0.50-1.50%, ■ 0.05-050%, Nil Q, Q 5-0.
50%, M (one or more of 10.05 to 050%), further CuO, 20 to 3.00%
, 00005~1.00%, Be o, o 1~
1 out of 2.00% species j,! Ishi 2$l or more
, t0%, and the remainder substantially consists of Fe. 3 C0.50-080% by weight, Stl. 50-2.50%, Mn Q, 5 Q-1.50
% and ■0.05~0.50%, Nll Q, Q 5
~0.50%, M. Contains one or more of 0.05 to 0.50%, and further contains 10.20 to 3.00% of Cl and CoQ. 05 to 1.00%, Be O, one or two or more of 01 to 2.00%, and Bo, 0005 to 0.0
100%, Or 0.20-1.00%, Ni0.2
Copper for springs having excellent resistance to setting, characterized in that it contains one or more of the following: 0 to 2.00%, 0.30% or less of rare earth elements, and the remainder substantially consisting of Fe. 4 G O, 50-0.80% by weight, S+'l
. 50-2.50%, MnO, 50-1.50%
and ■005~0.50%, Nil Q, Q 5~0
,50%,M. 005 to 0.50%, and further contains Ciu□, 20 to 3.00%, and CoQ. 05 to 1.00%, Be O, one or two or more of 01 to 2.00%, and Wo, 05 to 1.00%. Copper for springs having excellent fatigue resistance, characterized in that it contains one or two of 0.05 to 0.50% of Ta, and the remainder substantially consists of FO.