Role of TiC reinforcement in enhancing pitting corrosion resistance and hydrogen embrittlement resistance of additively manufactured martensitic stainless steel

This study systematically investigated the effects of TiC addition on the microstructure and hydrogen embrittlement (HE) behavior of laser powder bed fusion (LPBF) 15-5PH stainless steel. The addition of TiC refined the microstructure, transforming lath martensite into fine equiaxed grains and reducing the average grain size from 3.32 μm to 1.25 μm. Meanwhile, the retained austenite content increased by approximately 9.5%, accompanied by a reduction in kernel average misorientation (KAM). Transmission electron microscopy (TEM) analysis further revealed the formation of incoherent TiC/matrix interfaces and nanotwins. After TiC addition, the hydrogen content decreased from 3.12 ppm to 1.97 ppm, and the hydrogen embrittlement sensitivity, evaluated by the loss of elongation, decreased by approximately 75%. Fractography and electron backscatter diffraction (EBSD)-based crack propagation analysis demonstrated that large blocky retained austenite regions effectively deflected and hindered crack propagation. The improved HE resistance was interpreted as being associated with the synergistic effects of reduced local strain concentration, possible hydrogen trapping at incoherent TiC/matrix interfaces, and crack arrest by retained austenite.