Cr-Mo steels are considered to be susceptible to weld related reheat cracking. This study was instituted to determine the mechanisms for reheat cracking in these steels as well as to determine methods to successfully avoid reheat cracking. Two heats of 1 ¼ Cr- ½ Mo were used, one being calcium treated. Also used were three heats of 2 ¼ Cr - 1Mo, one being a conventional grade of 2 ¼ Cr - 1Mo calcium treated; and the other two being modified (with ¼ V) grades, one of which was calcium treated.

The reheat cracking susceptibility of the materials was first determined by the Gleeble technique. Subsequently, a new simple and versatile test was developed - the spiral notch test. The materials were evaluated by this new test and a good correlation was found between the two tests. The effects of multiple thermal cycles and PWHT on reheat cracking susceptibility were investigated. TEM/STEM studies were conducted to determine the carbide evolution kinetics in the CGHAZ during PWHT. A technique was developed to prepare specimens with pristine reheat cracks in order to study the prior austenite grain boundary segregation and its relation with reheat cracking susceptibility.