Elimination of Hydrogen Induced Cracks by Slow Cooling After Hot Rolling of Medium Carbon Molybdenum Steel Blooms

Abstract

At JSW Steel Limited, Salem Works (JSWSL), hydrogen induced cracks contribute more to ultrasonic defects in medium carbon molybdenum steel such as JDM 1046. As hydrogen tend to escape during cooling due to its smaller atomic radius and high diffusivity in the solid phase, experiments were conducted to reduce hydrogen induced cracks by slow cooling of blooms/bars. A study was conducted wherein few blooms/bars of the same heat were slow cooled and others were normal cooled (air cooled). After cooling, hardness, microscopic and ultrasonic examinations were carried out on these blooms/bars. Results revealed that, the slow cooled blooms/bars were found to be free from ultrasonic defects and showed reduced as rolled hardness when compared with air cooled blooms/bars. Slow cooling resulted in defect free steel against 15-35% defect levels observed in air cooled bars. The paper discusses various metallurgical changes, which facilitated the elimination of hydrogen in JDM 1046 grade steel.