Effect of Reduction Ratio Below Austenite Recrystallization Stop Temperature on Mechanical Properties of an API X70M PSL2 Line Pipe Steel

Özet

Steel grades having high toughness and high strength are required for line pipes since gas and oil should be transported through them at high pressures. Thermo-mechanically controlled rolling processes are used for increasing both toughness and strength at low temperatures since the line pipes are exposed to harsh climatic conditions at full length and rather severe service conditions. Charpy, DWTT and tensile tests were conducted to determine of mechanical properties and measured toughness values were evaluated considering various criteria in this study. Fractured surfaces were examined by means of SEM to distinguish the ductile and brittle fracture areas. Thermo-mechanical rolling trials were performed at the temperature below the non-recrystallization temperature of austenite on an API X70M PSL2 grade steel, to increase the strength without sacrificing the toughness. Different reduction ratios between 60,7% and 72,8% were utilized and the effect of reduction ratios on mechanical properties and microstructures were investigated during the trials. It was observed that final grain size decreased and strength and toughness increased with increasing reduction ratios.