Özet:
In this study, the effect of high austenitization temperatures to improve the mechanical properties of AISI 5140 steel was investigated. Firstly, a general understanding of iron-carbon syatem, transformation of austenite under both equilibrium and non-equilibrium conditions were given, and the concept of hardenability was introduced. Secondly, hardening and tempering of low alloy steels were viewed and then the atudies on high temperature austenitization were summarized. In the experimental work, the test specimens were auatenitized at either 845°C, 1000°C, 1100°C or 1200°C. The resulting martenasitic structures were tempered at either 200°C. or 570°C. Double austenitization -consisted of 1200°C austenitization followed by oil quenching; after the oil quenching, tempering at 200°C, and then reaustenitizing at 845°C- was also employed. Then, the mechanical properties were measured with hardness testing, tensile testing, Charpy impact testing, plane strain fracture toughnesa testing and Jominy end-quench testing. The resulting microstructures after different hardening treatments were studied by optical microscope. The fracture surfaces were examined USing scanning electron microscope (SEM).
