40CrMo8-mod 합금의 냉각속도와 템퍼링 온도가 미치는 미세조직 및 기계적 특성의 변화
40CrMo8-mod alloy effect of cooling rate and tempering temperature changes in microstructure and mechanical properties
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40CrMo8 steel is one of the representative medium carbon and low alloy steels. Due to its good balance of strength, toughness and wear resistance, 40CrMo8 high-strength steel is widely used for many general purpose parts including crankshaft, rams, spindles, etc. High strength Cr-Mo steels belong to a group of steels that can reach their full mechanical properties after quenching and tempering. Therefore, in this study, the quenching and tempering properties of the 40CrMo8-mod alloy steel used to the vessel crankshaft were investigated. In the case of tempering, the transformation of the martensite is clearly observed at 700℃ rather than 600℃, and the carbide gradually coarsened with increasing holding time. Tensile strength and yield strength were decreased with increasing temperature and holding time, and the values of the elongation and impact test were shown inversely. The curve of the tempering parameter was calculated by hardness test, and this curve could be used to predict the hardness values of the tempered 40CrMo8 alloy steel.