Precipitation-strengthened Fe-Ni based austenitic alloys possess high strength,excellent corrosion resis-tance,and low hydrogen embrittlement sensitivity,thus being widely used in sectors such as aerospace,hydrogen energy engineering,and petrochemicals.In comparison to existing casting and forging techniques,additive manufac-turing can achieve near-net shaping of intricately shaped components.NASA-HR(NHR)hydrogen-resistant steel was fabricated by laser melting deposition,and the effects of heat treatment process conditions,including high-temperature solid solution(930-1 180℃)and aging treatment(725-775℃),on its microstructural evolution,mechanical properties,and hydrogen-resistant properties are studied.The results indicate that due to the high tem-perature gradient and rapid melting rate during the laser melting deposition process,the solidification structure is pri-marily composed of columnar crystals,with Ti element segregation observed in the dendrite region.After solid solu-tion treatment at 1 180℃,the characteristic features of the NHR alloy melt pool during laser melting deposition dissi-pated,effectively eliminating Ti element segregation and achieving a uniformly recrystallized structure.Subsequent aging treatments at 725℃,750℃,and 775℃revealed that as the aging temperature rose,grain size slightly increased,with the size of γ' phase nano-precipitates gradually widening,leading to an enhanced precipitation strengthening effect and a significant rise in alloy strength.After aging at 775℃,the strength reached 1 070 MPa,with a slight reduction in plasticity;however,its elongation after fracture consistently exceeded 26％,and the tensile fracture morphology was characterized by ductile dimples,exhibiting ductile fracture characteristics.Optimizing heat treatment conditions can align the mechanical properties of NHR alloys produced via additive manufacturing with those of the forged state.The reduction in hydrogen-induced plastic damage for the NHR alloy in forging and addi-tive manufacturing is 21.7％and 20.8％,respectively,with comparable susceptibility to hydrogen embrittlement.After hydrogen charging,both tensile fracture surfaces exhibit intergranular fracture characteristics,indicating a mixed ductile-brittle fracture.The good matching of mechanical properties and hydrogen resistance of additive manu-facturing NHR alloy provides a reference for the service performance of additive manufacturing resistant steel in a hydrogen-friendly environment,and develops ideas for the application of additive manufacturing resistant hydrogen steel.
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