| Forge-quenching heat treatment of medium carbon steel mechanical properties, such as toughness and impact value, is widely used for quality improvement of hot working parts. In the present study, oxidation-decarburization phenomena were investigated in relation to heating temperature for closed die forging, and forge-quenching conditions were discussed in order to improve mechanical properties and to obtain uniform micro-structure. Decarburized depth was measured to be 0.5m/m at 1,200℃, 1-3m/m at 1,300℃, and 0.5m/m at 1,400℃. Excellent hardenability was obtained at high quenching temperature(950-1,050℃) by application of its self-heat in closed die forging of one heat system. Also uniform tempered structure and improved toughness were obtained at high tempering temperature(550-600℃). Thus, impact value of tempered medium carbon steel that was forge-quenched was doubled as compared with that of ordinary quenched steel. In view of the above results, it may be concluded that application of the forge quenching method makes it possible to replace alloy steel parts with carbon steel or to reduce the weight of carbon steel parts. |
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