Kobe Steel, Ltd.

Kabushiki Kaisha Kobe Seiko Sho (kobe Steel, Ltd.)

Atsuhiko Yoshida

Koichi Sakamoto

Tomoko Sugimura

Sumie Suda

Yoshio Fukuzaki

Takeshi Inoue

Sei Kimura

Hiroshi Yaguchi

Kei Masumoto

Goro Anan

Yoshiteru Fukuoka

High cleanliness spring steel useful in manufacturing a spring with SiO-based inclusions being extremely controlled and excellent in fatigue properties is provided. High cleanliness spring steel which is steel containing;

High cleanliness spring steel and high cleanliness spring excellent in fatigue properties

Disclosed is a spring steel which contains, by mass, 1.2% or less C; 0.1% to 2% Mn; 0.2% to 3% Si; 0.0003% to 0.005% Al; to 8 ppm Li; 30 ppm or less (excluding 0 ppm) Ca; and 10 ppm or less (excluding 0 ppm) Mg. The steel contains oxide inclusions satisfying the following conditions (1) to (3) in a number of 1&#xd7;10or more per square millimeter: (1) containing a total of 80 percent by mass or more of AlOand SiObased on the inclusion composition excluding LiO; (2) having a ratio by mass of AlOto SiOof from 1:4 to 2:3; and (3) containing lithium (Li). The spring steel gives a spring that exhibits superior fatigue properties without strict control of the average composition of inclusions.

Spring steel and spring superior in fatigue properties

High cleanliness spring steel useful in manufacturing a spring with SiO-based inclusions being extremely controlled and excellent in fatigue properties is provided.

An object of this invention is to provide a steel for high-cleanliness spring which is useful for the production of a spring excellent in fatigue characteristics in high Si steels. The steel for high-cleanliness spring with excellent fatigue characteristics according to the invention contains: in terms of mass %, C: 1.2% or less (excluding 0%); Si: 1.8% to 4%; Mn: 0.1% to 2.0%; and total Al: 0.01% or less (excluding 0%), with the remainder being iron and inevitable impurities, in which the Si amount and a solute (SIMS) Ca amount in the steel satisfy a relationship of the following expression (1):Si&#xd7;10&#x2266;solute (SIMS) Ca&#x2266;Si&#xd7;5&#xd7;10&#x2003;&#x2003;(1)(in which each of the solute (SIMS) Ca and Si represents the amount thereof (mass %) in the steel).

Steel for high-cleanliness spring with excellent fatigue characteristics and high-cleanliness spring

A low carbon resulfurized free-machining steel having a high machinability is provided. This steel comprises 0.02 to 0.15% by mass of C, up to 0.004% by mass (more than 0% by mass) of Si, 0.6 to 3% by mass of Mn, 0.02 to 0.2% by mass of P, 0.2 to 1% by mass of S, up to 0.005% by mass (more than 0%) of Al, 0.008 to 0.04% by mass of O, and 0.002 to 0.03% by mass of N; and the average oxygen concentration in the MnS in the steel is at least 0.4% by mass.

Low carbon resulfurized free-machining steel having high machinability

The present invention relates to a high-cleanliness steel having a high fatigue strength and high cold workability, and a method of making the high-cleanliness steel. The method adds a Li&#x2014;Si alloy having a Li content between 20 and 40% and/or LiCOas a Li-containing substance to a molten steel. The Li-containing substance is added to the molten steel after the completion of a series of steps of a ladle refining process including composition adjustment, temperature adjustment and slag refining. The high-cleanliness steel has a total-Li content between 0.020 and 20 ppm by mass and contains 1.0 or below oxide inclusion particle having a major diameter of 20 &#x3bc;m or above at a maximum in 50 g of the steel wire. The steel contains an oxide inclusion that has a CaO content between 15 and 55%, SiOcontent between 20 and 70%, an AlOcontent of 35% or below, a MgO content of 20% or below and a LiO content between 0.5 and 20%. The high-cleanliness steel has improved fatigue characteristics and improved cold workability.

Method for producing high cleanness steel excellent in fatigue strength or cold workability

Method for producing high cleanliness steel excellent in fatigue strength or cold workability

Disclosed herein is an ultra clean spring steel which contains inclusions easily elongated and broken into fine particles by hot rolling and which is easily adaptive to cold rolling and yields springs excelling in fatigue characteristics. The spring steel is characterized in that the wire contains oxide inclusions with a sulfur concentration no more than 10 mass % such that no less than 70% (in terms of numbers) of such inclusions, which exist in the outer layer outside one quarter of the diameter of the wire and have a width no smaller than 3 &#x3bc;m, satisfies the formula (1) below,CaO+AlO+SiO+MnO+MgO&#x3e;80 (mass %) . &#x2003;&#x2003;(1)

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Kobe, Japan

Atsuhiko Yoshida