Spring steel superior in fatigue properties

Details Spring steel superior in fatigue properties Spring steel superior in fatigue properties

1999-12-15

2001-12-11

King, Roy (Department: 1742)

Metal treatment

Stock

Ferrous

C148S540000, C148S908000, C148S333000, C420S105000

Reexamination Certificate

active

06328820

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spring steel superior in fatigue properties. More particularly, the present invention relates to a spring steel (for valve springs and the like) superior in fatigue properties which is characterized by a low content of undeformable inclusions.
2. Description of the Related Art
It is a well-known fact that such steels as used for valve springs, which need a high fatigue strength, are liable to fracture that starts from hard non-metallic inclusions if they contain them. In order to prevent fracture due to such hard inclusions, there have been proposed several ways to control their composition such that they have a melting point lower than 1500° C. Such hard inclusions are made smaller by hot or cold rolling or drawing.
There is disclosed a steel with a high degree of cleanliness in Japanese Patent Publication No. 74484/1994. This steel contains non-metallic inclusions whose average composition is SiO
2
: 20~60%, MnO: 10~80%, and CaO: 13~50%, and/or MgO: 5~15%. These non-metallic inclusions are characterized by that the ratio of length (l) to width (d) measured in the longitudinal cross-section of rolled steel is l/d≦5. There is also disclosed a steel with a high degree of cleanliness in Japanese Patent Publication No. 74485/1994. This steel contains non-metallic inclusions whose average composition is SiO
2
: 35~75%, MnO: Al
2
O
3
: ≦30%, CaO: 10~50%, and MgO: 3~25%. These non-metallic inclusions are characterized by that the ratio of length (l) to width (d) measured in the longitudinal cross-section of rolled steel is l/d≦5.
The steels with a high degree of cleanliness disclosed in the above-mentioned patents are designed to improve the fatigue properties by controlling the average composition of non-metallic inclusions such that the ratio of length (l) to width (d) is l/d≦5. The present inventors found that they have the following problems.
Even though the average composition of non-metallic inclusions is controlled so that l/d≦5, there still exist hard inclusions exceeding this limit and they cause breakage. Moreover, even though inclusions are ductile and satisfy the condition l/d≦5, they also cause breakage if they are thick.
OBJECT AND SUMMARY OF THE INVENTION
The present invention was completed in order to tackle the above-mentioned problems. It is an object of the present invention to provide a spring steel superior in fatigue properties.
The gist of the present invention resides in a spring steel superior in fatigue properties which is characterized in that oxide type inclusions therein have an average composition (by weight) specified as follows:
35%≦SiO
2
≦75%
5%≦Al
2
O
3
≦30%
10%≦CaO≦50%
MgO≦5% (excluding 0%)
According to a preferred embodiment of the invention, the spring steel is characterized in that oxide type inclusions thinner than 5 &mgr;m account for more than 80% (in number) of total oxide type inclusions in the longitudinal cross-section of rolled steel.
Moreover, for improved fatigue properties, the spring steel should be produced such that its surface defects have a depth less than 1.0% of its diameter and its total decarburized depth is less than 1.0% of its diameter.


REFERENCES:
patent: 5415711 (1995-05-01), Takagi et al.
patent: 5651937 (1997-07-01), Descaves
patent: 6123784 (2000-09-01), Havette
patent: 1 010 769 (2000-06-01), None
patent: 62-099437 (1987-05-01), None
patent: 02-034748 (1990-02-01), None
patent: 04-006211 (1992-01-01), None
patent: 06-145895 (1994-05-01), None
patent: 06-158226 (1994-06-01), None
Patent Abstracts of Japan, vol. 1998, No. 09, Jul. 13, 1998, JP 10-102131, Apr. 21, 1998.
Chemical Abstracts, vol. 112, No. 2, Jan. 8, 1990, AN 10285, T. Ohshiro, et al., “Improvement of the Service Life of Valve Spring Wire”, 1989.

Affiliated with

Also associated with

Rating

Spring steel superior in fatigue properties does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Spring steel superior in fatigue properties, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spring steel superior in fatigue properties will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2571042