• RAKESH ROSHAN

      Articles written in Sadhana

    • Continuous cooling transformation diagram and mechanical properties in weld coarse-grain heat-affected zone of API X70 steel

      AJIT KUMAR NAIK RAKESH ROSHAN KANWER SINGH ARORA NIKHIL SHAJAN SUBASH CHANDRA MISHRA

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      In the present work, continuous cooling transformation (CCT) of coarse-grained heat-affected zone (CGHAZ) and simulation of Charpy-sized impact specimens were performed using a Gleeble 3800 thermomechanical simulator. Results obtained from the dilation studies show significant effect of cooling rates onmicrostructure and low-temperature (–20 ΟC) Charpy impact toughness. Phase transformation temperatures (Ar3 and Ar1) and impact toughness decreased while hardness and amount of bainite increased with increasing coolingrates. At slow cooling condition (\ 5 ΟCs-1) quasi-polygonal ferrite and pearlite phases were observed in the microstructure. At medium cooling rate (5–25 ΟCs-1), bainite and quasi-polygonal ferrite were obtained in the microstructure. For still faster cooling rates, microstructure was completely bainitic in nature. Themicrostructures were confirmed by hardness measurement where the hardness value for lower, medium and high cooling rates were 191–196, 213–214 and 234–253 HV, respectively. Charpy impact toughness increased with decrease in cooling rate due to the presence of softer ferrite phase.

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