JPH0578785A - High strength spring steel - Google Patents

Abstract

PURPOSE:To provide high strength spring steel used in an automobile, various vehicles, aeronautical machinery, various industrial machines, etc. CONSTITUTION:This high strength spring steel consists of, by weight, 0.50-0.70% C, 1.00-2.50% Si, 0.50-1.20% Mn, 0.80-<1.20% Cr, 0.05-0.30% Mo, 0.05-0.30% V, 0.01-0.30% Nb, 0.005-0.100% Al and the balance Fe with inevitable impurities, withstands repeated use and has a long service life and excellent sag resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high strength steel for springs used in automobiles, various vehicles, aviation equipment, various industrial machines and the like.

[0002]

2. Description of the Related Art In recent years, automobiles have been strongly required to be lightweight in order to reduce fuel costs. This demand extends to various parts, and suspension systems are no exception. As one of the countermeasures, it is possible to increase the design stress of the suspension spring. That is, it is effective to increase the strength of the spring. Currently, as suspension steels, JIS SUP7 is mainly used in the Si-Mn steel system, and SUP12 is used in the Si-Cr steel system. However, in order to further increase the design stress, these steel types have high strength. It is necessary to use the converted one.

In general, the strength of a steel material has a strong correlation with the altitude, and therefore, increasing the strength means increasing the hardness.

[0004]

However, if the hardness of the spring steel is increased, there is a concern that the toughness such as the Charpy impact value may decrease. In short, the reduction of toughness was unavoidable in order to obtain hardness higher than that of the current spring steel. Therefore, when increasing the hardness of the suspension spring to improve its strength,
In order to guarantee its reliability, it was necessary to have toughness higher than that of the current steel.

[0005]

As a result of investigating the influence of various elements on hardness and toughness, the present inventors have obtained the following relational expression.

Hardness (Hv) = 460 + 112.6 (C
%) + 46.82 (Si%) + 4.581 (Mn%) +
21.11 (Cr%) + 14.20 (Mo%) + 17
2.2 (V%)-158.0 (Nb%)-122.3
(Al%) (1) Formula Toughness (JIS No. 3 Charpy impact value kgf-m / c
m ² ) = 2.297-1.166 (C%) + 0.504
(Si%)-0.130 (Mn%) +0.505 (Cr
%) + 1.904 (Mo%) + 1.260 (V%) +
3.993 (Nb%) + 9.643 (Al%) ... (2)
Formula However, the above relational formula is a calculation formula in the case where each of the steels under test is sufficiently martensitic by quenching and tempered at a temperature of 380 ° C. From these results, it was found that hardness and toughness have a very high correlation with the alloying elements. That is, to obtain high hardness,
The amounts of C, Si, Mn, Cr, Mo and V are adjusted respectively, while Si, Cr, Mo, V,
The present invention has been completed based on the finding that a high-strength spring steel having high hardness and high toughness can be obtained by adjusting the amounts of Nb and Al.

That is, in the present invention, in% by weight, C: 0.5
0 to 0.70%, Si: 1.00 to 2.50%, Mn:
0.50 to 1.20%, Cr: 0.80 to less than 1.20%, Mo: 0.05 to 0.30%, V: 0.05 to 0.
30%, Nb: 0.01 to 0.30%, Al: 0.00
A high-strength spring steel characterized by containing 5 to 0.100% and the balance being Fe and inevitable impurities.

[0008]

The reasons for limiting the components in the present invention are as follows.

C: C is an element effective for increasing the strength of steel, but if it is less than 0.50%, the required strength as a spring cannot be obtained, and if it exceeds 0.70%, the spring becomes brittle. Since it is too high, the range is set to 0.50 to 0.70%.

Si: Si is an element effective in improving the strength of steel by forming a solid solution in ferrite.
If it is less than 1.00%, the required strength as a spring cannot be obtained, and if it exceeds 2.50%, decarburization of the surface is likely to occur during hot forming of the spring, and the durability of the spring is improved. Since it gives a bad influence, it was set within the range of 1.00 to 2.50%.

Mn: Mn is necessary for improving the hardenability of steel, and its optimum range is 0.50 to 1.20%.

Cr: Cr is an element effective for increasing the strength of steel, but if it is less than 0.80%, it cannot provide the necessary strength as a spring, and if added in an amount of 1.20% or more, it is effective. Is saturated, so the range is 0.80 to 1.20%
Less than

Mo: Mo is an element that secures the hardenability of steel and enhances the strength and toughness of steel, but if it is less than 0.05%, these effects cannot be fully expected, and 0 .3
If it exceeds 0%, coarse carbides are likely to precipitate and the spring characteristics are deteriorated, so the range was made 0.05 to 0.30%.

V: V is an element that enhances the strength of steel,
If it is less than 0.05%, its effect cannot be sufficiently expected, and if it exceeds 0.30%, the amount of carbides that are not dissolved in austenite increases and the spring characteristics deteriorate, so the range is set to 0.05. Was set to 0.30%.

Nb: Nb is an element for refining the crystal grains and improving the toughness. If it is less than 0.01%, its effect cannot be expected sufficiently, and if it exceeds 0.30%, in austenite. Since the amount of carbides not dissolved in the steel increases and the spring characteristics are deteriorated, the range is set to 0.01 to 0.30.
%.

Al: Al is an element necessary for adjusting the deoxidizing agent and austenite grain size of steel, and
If it is less than 005%, the crystal grains cannot be made finer.
If it exceeds 100%, the castability tends to be lowered, so the range was made 0.005 to 0.100%.

The steel of the present invention has the above-mentioned components, but in the production thereof, the spring steel is produced through the steps of ordinary steelmaking, ingot making or continuous casting, slab rolling, bar steel rolling or wire rod rolling. Obtainable. Thereafter, processing such as hot coil spring forming, quenching, tempering, shot peening and setting is performed to obtain a high strength coil spring.

[0018]

[Examples] Table 1 shows the chemical compositions of the steels of the present invention, examples and comparative examples.

[0019]

[Table 1]

380 after quenching for each sample steel shown in Table 1
Table 2 shows the relationship between hardness and Charpy impact value when tempered at ℃.

[0021]

[Table 2] The relationship between the results in Table 2 and the predicted values obtained from the equations (1) and (2) is shown in FIGS. 1 and 2, respectively. It can be seen from Table 2 that the invention steel has a higher Charpy impact value than the comparative steel.

Inventive Steel No. 7, comparative steel No. No. 22 was used to make a steel ingot, which was hot-rolled at a rolling ratio of 50 or more, and these steel materials were hot-spring-formed, quenched, tempered, shot peened, and set to obtain a test spring.

Table 3 shows the specifications of the test spring. The hardness of the spring was adjusted so that the invention steel was Hv620 and the comparative steel was Hv530.

[0024]

[Table 3] A durability test was performed using these test springs. The results are shown in Table 4.

[0025]

[Table 4] It is shown that the invention steel can secure the same life even if the stress is increased as compared with the comparative steel.

Table 5 also shows the results of the tightening test of the test spring.

[0027]

[Table 5] (Test condition: 80 ° C. × 96 hr) It is shown that the invention steel can secure the same sag resistance as the comparative steel even under the condition of higher stress than the comparative steel. That is, the invention steel is a high-strength spring steel that can be applied to springs used under higher stress than conventional steels. Therefore, since the Charpy impact value is high even when the strength is high, that is, the hardness is high, the reliability of the spring can be ensured.

[0028]

INDUSTRIAL APPLICABILITY The steel of the present invention is a high-strength spring steel having excellent durability and life and sag resistance when applied to springs, and is incorporated as a mechanical element in various industrial equipment including automobiles. Is big.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a calculated value of hardness of steel and an actually measured value.

FIG. 2 is a graph showing a relationship between a calculated value of steel toughness and an actually measured value.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuyuki Uchibori 1-9-31 Shinonome, Koto-ku, Tokyo Inside the Technology Development Center, Mitsubishi Steel Corporation (72) Inventor Hiroharu Motomura 1-9 Shinonome, Koto-ku, Tokyo −31 Inside the Mitsubishi Steel Co., Ltd. technology development center

Claims (1)

[Claims] 1. C: 0.50 to 0.70% by weight,
Si: 1.00 to 2.50%, Mn: 0.50 to 1.2
0%, Cr: 0.80 to less than 1.20%, Mo: 0.0
5 to 0.30%, V: 0.05 to 0.30%, Nb:
0.01-0.30%, Al: 0.005-0.100
%, The balance being Fe and inevitable impurities, a high strength spring steel.