Effect Of Quenching and Tempering Temperature on the Fracture Quality of GS-45CrNiMo4-2 Steel, Through the Quench-Temper Heat Treatment Cycle

In this study, was exposed to various Quench-Temper heat treatment cycles. Structural analyzes, mechanical tests (tension and impact) as well as analyzing the fracture surfaces of tension tests for models exposed to quenching environments (100 ͦ C and 200 ͦ C) and tempering (250 ͦ C-500 ͦ C) with austenitic temperature of 800 ͦ C, were performed. The amounts of stiffness, tensile strength and impact energy of the original raw material were 20 HRC, 724MPa and 20J, respectively. Results showed that after the heat treatment cycles, the amounts of stiffness in oil 100 ͦ C and 200 ͦ C were 50 and 55 HRC respectively, and tensile strength and impact energy for both quenching environments were near 1730 MPa and 7 J. With tempering from 250 ͦ C to 500 ͦ C, stiffness and tensile strength were decreased, and ductility and impact energy were increased (up to 40J). Also, under the quenching environment of oil with temperature of 200 ͦ C, secondary stage stiffening occurred due to more remaining austenite at tempering process temperature of 350 ͦ C. Through the tempering process, A good combination of ductility and impact energy were not achieved at 250 ͦ C and the cleavage mode of fracture at this temperature was observed. At temperatures above 500 ͦ C, ductile fracture was observed and between 250 ͦ C and 350 ͦ C, the outcome was semi-cleavage (brittle + ductile) fracture.