Sugita Wire Mfg. Co., Ltd.

Heiji Sugita

Takehiko Kato

Yoshitaka Nitta

Hiroharu Sawada

Masao Toyama

Disclosed herein is a new method for continuous heat treatment to be applied to the production of oil tempered steel wires for springs having high strength and high toughness to meet the requirement for weight reduction. The heat treatments are applicable to a medium carbon low alloy spring steel which does not undergo martensitic transformation substantially upon oil hardening alone. It comprises performing two-step accelerated hardening consistin of oil hardening and immediately following water hardening and subsequently performing tempering. The medium carbon low alloy steel is one which consists 0.40-0.65% carbon and Si and Mn as essential components and further at least one species of Cr, Ni, Mo, and V, and have the chemical composition corresponding to and Mf point lower than 80.degree. C. (preferably 10.degree.-70.degree. C.). It is desirable that the oil be wiped from the steel wire after the oil hardening and before the water hardening.

Method for producing by continuous heat treatments oil-tempered steel

There is provided an oil tempered and hard drawn steel wire for springs which comprises having a phosphate coating on the surface thereof if necessary, high strength, and a shaped cross section free of twist in the longitudinal direction. It is produced by oil tempering, descaling, and phosphate treatment if necessary, and cold working. Having a shaped cross section free of twist in the longitudinal direction, the steel wire can be formed into high quality springs in which the individual cross sections of the wire are arranged regularly in the same direction. The steel wire is particularly suitable for making springs.

Process for producing oil quench hardening and tempering and hard drawn

A high strength bolt having a as-formed structure and a method of manufacturing the high strength bolt which method comprises the steps of: heating a steel alloy containing 0.15 to 0.3 wt % C and 1 to 3 wt % Mn to a temperature not lower than Ac.sub.3 transformation point; subjecting the steel alloy to isothermal transformation at 450.degree. to 580.degree. C.; subjecting, after cooling, the steel alloy to cold wire drawing at a reduction rate not larger than 40%; and bolt forming the steel. A cold wire drawing at a reduction rate not larger than 40% may be carried out before the above-mentioned isothermal transformation step.

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Ichikawa, Japan

Heiji Sugita