日本金属学会誌

J. Japan Inst. Metals, Vol. 54, No. 2 (1990),
pp. 231-236

Heat-Treatment and Machinability of the Tri-Phase Steel Composed of Ferrite, Martensite, and Graphite

Hidekazu Sueyoshi1 and Ryohei Tanaka2

1Department of Mechanical Engineering, Faculty of Engineering, Kagoshima University, Kagoshima
2Department of Mechanical Engineering and Materials Science, Faculty of Engineering, Yokohama National University, Yokohama

Abstract:

For the purpose of developing a structural steel having both excellent plasticity and machinability in addition to a high tensile strength, heat-treatment for the tri-phase steel composed of ferrite, martensite, and graphite is examined and the machinability of the tri-phase steel is studied by comparing with that of the dual phase steel composed of ferrite and martensite. The results obtained are summarized as follows.
(1) By means of a series of three-stage heat-treatments constructed from quenching as pre-treatment, partial graphitization at a temperature just below A1, and quenching from a temperature just above A1, the tri-phase steel in which fine graphite nodules and fine martensite are dispersed in ferrite matrices can be obtained.
(2) The tri-phase steel is low in cutting force as compared with the dual phase steel because of the decreases of shear stress and friction angle and an increase of shear angle with the presence of the graphite nodules.
(3) The tri-phase steel is slightly inferrior to the dual phase steel in surface roughness after machining because the graphite nodules promotes the formation of micro-crack in the neighborhood of a tool edge.
(4) The drillability of the tri-phase steel is considerably superior to that of the dual phase steel.


(Received 1989/8/30)

Keywords:

martensite, graphite, tri-phase steel, dual phase steel, heat-treatment, machinability


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