Different aspect of solidification cracking susceptibility and hot ductility behavior of borated stainless steels and the effects of boron content

摘要

A series of austenitic Fe-0.06wt%C-1.5wt%Mn-18wt%Cr-12wt%Ni stainless steels with B additions ranging from 0.2 to 1.76 wt% were prepared and the weldability of these samples was evaluated through Varestraint cracking tests and Gleeble hot ductility tests. The base steels consisted of the austenite(gamma) matrix and borides of Cr-enriched M2B (Cr2B), and the fraction and size of the Cr2B borides increased with an increase in the B content. The results of the Varestraint cracking tests indicated that the resistance to solidification cracking in the fusion zone was improved with an increase in the B content and this is because the extent of solidification temperature range reduces with an increase in the B content. In the fusion zone, cracks occurred at the interphase between the primary gamma and gamma/Cr2B eutectic during solidification. At the heat-affected zone (HAZ) near the fusion zone, constitutional liquation occurred around the Cr2B borides, after which the gamma/Cr2B eutectic formed surrounding Cr2B borides during cooling. Interestingly, the results of the hot ductility tests were in direct contrast to those of the Varestraint cracking tests; i.e., the hot ductility in the HAZ decreased with an increase in the B content. This occurred because cracks initiated and propagated along the gamma/Cr2B interphase, and then the fraction and size of the brittle Cr2B borides acted as crack initiation site increased with an increase in the B content.