Tempering Process Gradually to Improve Quality Tool

摘要

Tempering is a heating treatment process to improve the elasticity with a little hardness. It is reheating the steel that has been hardened under the critical temperature of 723°C and applying a holding time at that temperature, then cooling the steel in the air outside. The hardening was followed by gradual tempering process at different temperatures of 650°C, 550°C and 450°C at 60, 120, and 180-minute holding times. The tempering process resulted in hard and tough not easily broken or worn tool steel. Besides, it improves the tensile strength and increases the durability of tool against collision. Tukey, Fisher Pairwise Comparison and Dunnet Method were applied to obtain Grouping Information data of 93%. Observations on eight tempering treatment processes show not only treatments 4, 5 and 6 (tempering with time delay) but also gradual tempering (in which the process was done some times by gradually dropping the temperature) resulted in better performance. Further observation was conducted in terms of the variation of dropping temperature and the most optimum holding time of the tempering process. Processes 7 and 8 (tempering without time delay) are not recommended, as the hardness value drops sharply, high vibration occurs when machining, and the cutting results in high roughness value.