EFFECT OF HOT ROLLING ON FRACTURE AND FATIGUE BEHAVIOR OF P92 STEEL

Abstract

In the present project investigation, systematic studies on microstructure and mechanical properties of P92 steel subjected to various normalizing (1000ºC-1100ºC) and tempering (720ºC -750ºC ) temperatures is carried out at room temperature and high temperature. The effect of heat treatment on microstructure revealed increase in grain size but it was significantly small. Tempered martensite is observed in tempered heat treated specimen which is favorable for creepfatigue failure. The ultimate tensile strength reduces with increase in tempering temperature while the ductility is shown to improve. The coarsening of precipitates is observed with increase in tempering temperature. At very high temperature range (1000-1100°C) prior austenite grain boundaries were dissolved. P92 steel normalized at 1000ºC and tempered at 720ºC is found to have best combination of strength and ductility. Hot rolling of P92 steel is performed at normalizing temperature 1000°C and tempered at 720°C to study the combine effect of heat treatment and rolling. The yield strength of thermo-mechanically treated P92 steel was significantly improved by 22% and 12% at room temperature and 650°C respectively with a fine grain structure and increased dislocation density. Fracture tests are also performed to study the effect of hot rolling and optimum heat treatment. The fracture toughness for the optimum condition (i.e. normalized at 1000 0C and tempered at 720 0C) is found to be maximum (i.e. 576 N.mm/mm2) proceeded by hot rolling (i.e. 536 N.mm/mm2) as compared to as-received (i.e. 473 N.mm/mm2). Fatigue crack growth (FCG) behaviour of as received and hot rolled P92 steel has been investigated in Paris regime. The hot rolled steel sustains less no of cycles for same crack extension as compared to as-received condition.