Joining Ferritic SA508 Low Alloy Steel to Austenitic 316L Stainless Steel by Powder Metallurgy via Hot Isostatic Pressing
Type of DegreeMaster's Thesis
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As an alternative to traditional welding, the joining of low alloy steel and austenitic stainless steel using powder metallurgy by hot isostatic pressing was evaluated as a method to join two dissimilar metals. This study examined the microstructure, mechanical properties, and sensitization of two joint designs subjected to a variety of heat treatments: powder SA508 (P508) to bulk 316L (B316L) and powder P316L (P316L) to bulk SA508 (B508). The grain refinement and coarsening induced by solution annealing, normalization, and tempering improved the interface's toughness. The tensile test produced a satisfactory yield strength, and heat treatment reduced the microhardness values along the interface. At the interface between P508-B316L and P316L-B508, however, a notable reduction in impact toughness was observed. The presence of large oxide inclusions at the interface of P508-B316L and the high degree of sensitization on the P316L side of P508-B508 due to the precipitation of chromium-rich carbides (M23C6) caused a reduction in toughness. PanDiffusion was used to simulate the carbon profile and M23C6 carbides as a function of distance to address this issue. By lowering the tempering temperature, the nucleation of carbides was observed to be reduced, but high concentrations of carbides still facilitated the region close to the interface. In conclusion, it was not feasible to join 316L to SA508 by PM-HIP, and a transitional metal, such as a Ni-alloy or a functionally graded material composed of 316L and SA508, is required to minimize carbide precipitation.