Roles of Molybdenum and Tungsten on Reheat Cracking Susceptibility of 2.25Cr Heat Resistant Steels

Abstract

The rupture time of the tungsten-alloyed steel is much shorter than that of the molybdenum-alloyed steel. The fracture mode of the former steel is typically intergranular, but the latter steel shows a mixed fracture mode of intergranular and ductile. The shorter rupture time of the tungsten-alloyed steel is due to the active carbide formation reaction of tungsten in ferrite which depletes carbon within the matrix; the resulting higher segregation concentration of phosphorus at GCls and carbide-free PAGBs. The longer rupture time of the other steel arises from two factors: the molybdenum segregated at the interfaces as a grain boundary strengthener; the repulsive segregation between carbon and phosphorus which repels phosphorus from the interfaces and produces the lower segregation concentration of phosphorus.