黒鉛を含む高Si-Mn鋼の機械的性質におよぼす二，三の熱処理の影響

Abstract

In the present work, the graphitic high Si-Mn steel (chemical compositions in most cases, 0.54%C, 1.0∼2.5%Si, 0.5∼0.9%Mn) was investigated to clarify the mechanical properties, being compared with the high-carbon graphitic forged steels (1.2∼1.6%C, 0.7∼1.3%Si). The heat-treatments studied, were normalizing, tempering after oil quench and tempering after normalizing. The results obtained were as follows: (1) In the longitudinal section (direction of forging), the fine flaky and directionally oriented graphite, which is often observed in high-carbon graphitic forged steel, was not seen in this steel. In the case of the specimen of chemical composition 0.85%C, 2.44%Si, nodular graphite appeared even by ferritic treatment. (2) Specimens tempered after oil quenching have better impact value, higher tensile strength, higher yield point and higher yield ratio than those tempered after normalizing. (3) Specimens tempered at 680°C for 5 hours after oil quenching showed almost constant values in tensile strength, yield point and hardness, not influenced by the carbon content. Reduction of area and elongation of specimens attained the maximum value at carbon content of 0.54%C. (4) Of the specimens in the range of 1.0∼2.5%Si and 0.54%C, those of 2.0%Si showed few scattering of values of reduction of area and elongation, and showed the tendencies of higher tensile strength and yield point. (5) Water cooling after tempering gave a better impact value than slow cooling. (6) The mechanical properties of graphitic high-Si-Mn steel in the present work were compared with those specified by JIS (Japan industrial standerds).