Strength of 444 Stainless Steel Single-Lap Joints Brazed with Ni-Based Metallic Glass Foils for Corrosive Environments

Abstract

The tensile strengths, σ_SLJ, of 444 stainless steel single-lap joints (SLJs) brazed with two corrosion-resistant Ni-based braze filler metals (BFMs) were investigated and compared with results from joints made from 316L stainless steel using identical BFMs and processes. In previous work, we proposed that σ_SLJ could be understood in terms of SLJ geometry (primarily the ratio of overlap length o to plate thickness t—which determines the stress state), base metal properties (which determine stress state evolution with load), and braze microstructure (which determines local failure stress). The geometry and braze microstructure were varied in the prior work. The present study shows the effect of the base metal. 444 has higher yield stress, lower ultimate strength, and less strain hardening than 316L, and also experiences significant grain growth above 1100 °C. Although the braze microstructures of SLJs made using 444 are very similar to those of their 316L counterparts, not only σ_SLJ, but also variations of both σ_SLJ and failure mode with o/t are very different. Differences are not simply due to ultimate strength as is commonly assumed, but to how plasticity controls joint rotation and thus stress state during loading, as well as through-thickness grain boundaries acting as failure sites.