Circumventing cracking in grading 316L stainless steel to Monel400 through compositional modifications

TL;DR

This study develops a new criterion for predicting hot cracking in the joining of stainless steel 316L and Monel400, using compositional modifications and functionally graded materials to improve weld integrity.

Contribution

A novel hybrid Scheil-equilibrium based hot cracking criterion was created and validated for joining Fe-alloys and Cu-alloys, aiding FGM design.

Findings

Validated the new cracking criterion with multi-layer samples.

Demonstrated reduced cracking through Ni gradient modifications.

Applied the method to direct energy deposition fabrication.

Abstract

In joining Fe-alloys and Cu-containing alloys to access the high strength of steels and corrosion resistance of Cu-alloy, cracking is widely observed due to the significant Cu microsegregation during the solidification process, resulting in an interdendritic Cu-rich liquid film at the end of solidification. By fabricating functionally graded materials (FGMs) that incorporate additional elements like Ni in the transition region between these terminal alloy classes, the hot cracking can be reduced. In the present work, the joining of stainless steel 316L (SS316L) and Monel400 by modifying the Ni concentration in the gradient region was studied. A new hot cracking criterion based on hybrid Scheil-equilibrium approach was developed and validated with monolithic multi-layer samples within the SS316L-Ni-Monel400 three-alloy system and an SS316L to 55/45 wt% SS316L/Ni to Monel400 FGM sample fabricated by direct energy deposition (DED) process. The new hot cracking criterion, based on the hybrid Scheil-equilibrium approach, is expected to help design FGM paths between other Fe-alloys and Cu-containing alloys as well.