چكيده به لاتين
All of hot work tool steel are usually used after quench and tempering. But todays, this heat tratment does not meet the required properties of these steels. Subzero and short time temper heat treatments proposed to improved properties of these steels. Therefore, the purpose of this study is investigation of the effect of subzero and short time temper heat tratments on microstructural and mechanical properties of Böhler W360 steel, Böhler H13 steel and W360 steel that produced in Iran. For this purpose, the steels were austenitized at 1050 ° C for 20 minutes and quenched in Vacuum furnace. After austenitization steels were tempered at 550, 610 and 580 ° C at each temperature for two hours, respectively that called common tempered. After the common temper, yield strength of Böhler W360, W360 cast in Iran and Böhler H13 steel were 1479 MPa, 1186 MPa and 1207 MPa, respectively. After austenitization, another series of samples were subjected to sub-zero heattreatment at minus 196 ° C in liquid nitrogen at two holding times of 14 and 28 h and also at minus 80 ° C in dry ice at two holding times of 14 and 28 h. The highest hardness was 66.5 HRC that was obtained by Böhler W360 steel after holding for 14 hours in dry ice. In order to perform short time tempering heat treatment, another series of all three steels after austenitition at 1050 ° C for 20 minutes, firstly tempered at 550, 600, 650 and 700 ° C for 10 minutes and then at 600 ° C secondary tempering was performed on them for 30 minutes. The highest hardness was obtained in Böhler W360 steel after short-time temper at 600 °C with 57 HRC. Also, the highest yield strength and tensile strength of Böhler W360 steel was obtained after short time tempering heat treatment at 550 ° C and 600 ° C with the yield strength 1775 MPa and tensile strength 2127 MPa respectively.
