EFFECTS OF CRYOGENIC TREATMENT ON MICROSTRUCTURE AND WEAR RESISTANCE OF Fe-0.35C-6.3Cr MARTENSITIC STEEL

Abstract

The study is conducted to determine the effect of quenching and tempering processes on microstructural evolutions and abrasive properties of medium carbon-high chromium steel. For this purpose, Austenitizing was performed at the temperatures of 1000 °C for 15 min followed by oil quenching. To determine the optimum tempering temperature, tempering temperatures were selected in the temperature ranges of 350-550°C. The samples cryogenically treated immediately after quenching in liquid nitrogen (-196°C) for 24 hrs. Dry sand/rubber wheel test was used to evaluate the wear resistance properties. Microstructural observation, fractography and retain austenite was evaluated by optical and scanning electron microscopy and X-ray diffraction analysis. The results show that the best wear resistance can be obtained at the tempering temperature of 500°C, due to the reduction of a tendency to micro-cracking, decrease in internal stresses and improvement of impact energy. Observation of the worn surfaces revealed that the wear mechanisms after tempering at 450°C are a combination of abrasive, adhesive and fatigue wear. However, abrasive wear is the only active wear mechanism for specimen tempered at 500°C. In addition, wear resistance of deep cryogenically treated sample was significantly increased (about 25%) by the removal of retained austenite and formation of uniform fine carbides distribution in the matrix.