Analysis of surface and sub-surface initiated spalling of forged cold work rolls

Two spalling behaviors of forged cold work rolls were analyzed. The results show that both the spalling behaviors are typical premature failure with different initiation mechanism. The presence of oxide inclusions induced the sub-surface initiation of rolling contact fatigue cracks in roll A while micro-crack initiated at roll working surface caused the spalling of roll B. Not only the high metallurgical quality of roll materials in manufacturing but also the proper operation in rolling process should be taken into consideration in order to preventing premature failure. Furthermore, eddy current and ultrasonic inspection techniques should be used after completion of the grinding operation to insure any surface and sub-surface defects is eliminated.