Stahlwerke Peine-salzgitter Ag

Gerhard Kiefer

Constantin M Vlad

Hans Paulitsch

Ullrich Koch

Alfred Babilon

Kurt Koerfer

A steel wire after coming from the mill is brought to a temperature between 850.degree. and 910.degree. C. This is followed by multi-stage water-cooling of the wire in such a manner that the surface of the wire is cooled to below the martensite start temperature while austenite is retained in the core of the wire. The heat retained in the core of the wire serves to partially temper the martensite formed at the surface of the wire. The wire is coiled while the temperature remains substantially constant so that the retained austenite in the core of the wire undergoes an isothermal transformation to fine pearlite. The heat of transformation serves to complete tempering of the martensite. After coiling, the wire is air-cooled to room temperature. The final wire exhibits a structure consisting of an outer layer of tempered martensite and a core of fine pearlite. This structure imparts excellent cold-working characteristics to the wire.

Method of making a steel wire adapted for cold drawing

A steel wire is rolled while in the austenitic range. Thereafter, the wire is cooled to a temperature between 850.degree. and 910.degree. C. This is followed by multi-stage water-cooling of the wire in such a manner that the surface of the wire is cooled to below the martensite start temperature while austenite is retained in the core of the wire. The latter cooling step brings the temperature of the surface of the wire to below the martensite start temperature in approximately 0.2 seconds. The heat retained in the core of the wire serves to partially temper the martensite formed at the surface of the wire. The wire is then coiled while the temperature remains substantially constant so that the retained austenite in the core of the wire undergoes an isothermal transformation to fine pearlite. The heat of transformation serves to complete tempering of the martensite. After coiling, the wire is air-cooled to room temperature and exhibits a structure consisting of an outer layer of fully tempered martensite and a core of fine pearlite. This structure imparts excellent cold-working characteristics to the wire since both the tempered martensite and the fine pearlite may be readily cold-drawn and, in addition, the tempered martensite at the surface of the wire possesses great strength which enables the stresses generated during cold-working to be transmitted along the wire. The reduction of area of the wire during cold-working may amount to 85 percent and more.

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Salzgitter-Lebenstedt, Germany

Gerhard Kiefer