Effect of Heat Treatments on the Microstructures and Mechanical Properties of OCTG

유정용 강관의 미세조직 및 기계적 성질에 미치는 열처리의 영향

  • Received : 2017.01.23
  • Accepted : 2017.05.12
  • Published : 2017.05.31


This study examined the effect of heat treatment on the microstructure and mechanical properties of J55 line pipe steel. The experiments were carried out at under the following various conditions: austenization temperature($880^{\circ}C$, $910^{\circ}C$, $940^{\circ}C$), cooling methods(water quenching, oil quenching) and tempering temperature(none, $550^{\circ}C$, $650^{\circ}C$). The phase diagram and CCT curve were simulated based on the chemical composition of J55 steel to predict the microstructures. In the results, A1, A3 temperature decreased. As the austenization temperature increased, existing austenite grains grew exponentially which seriously degraded their mechanical properties. Various microstructures, including martensite, bainite, ferrite, and pearlite, developed in accordance with the heat treatments and were closely correlated with hardness, tensile strength and toughness. Martensite was formed after water quenching, but bainite and ferrite appeared after oil quenching. FeC precipitation formed and coarsened during tempering, which improved their toughness.


Heat treatment;Mechanical property;Microstructure;OCTG;Quenching


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