低合金構造用鋼の黒鉛化を促進するための前処理

Abstract

For the purpose of realizing rapid graphitization in a low alloy structural steel (0.24 wt%C, 1.42 wt%Si and 2.13 wt%Ni), the effects of pre-quenching, pre-cold rolling and graphitization temperatures on the graphitization rate were studied by means of dilatometric measurements and optical microscopic observations. The main results obtained were as follows. (1) The time required for 50% graphitization, τ50, showed charactaristic C curve behavior with changing graphitization temperature, and the noses of the C curves, i.e. the temperatures of the highest graphitizing rate, were in the range of 923∼973 K. (2) The effects of pre-quenching were remarkable and rather complex, where the smallest τ50 of about 1 h (the highest rate), was obtained when pre-quenched from the temperature just above Ac1 and graphitized at 973 K. (3) The effect of pre-cold rolling was simpler and weaker than that of pre-quenching and τ50 decreases monotonically with increasing reduction of thickness. (4) The number of graphite nodules in the specimens also changes remarkably with pre-treatments and graphitizing temperatures, and the most dense and the finest graphite nodules (average diameter of ca. 0.3 μm) were obtained when pre-quenched from the temperature just above Ac1 and graphitized at 777 K.