Effect of heat treatment on the hydrogen embrittlement susceptibility of selective laser melted 18Ni-300 maraging steel

The effects of heat treatment on the hydrogen embrittlement (HE) susceptibility of selective laser melted 18Ni300 maraging steel were investigated. The results demonstrate that the as-built steel has a microstructure consisting of an Fe-Ni martensite matrix and a cellular structure. Substantial microstructural changes are observed following various heat treatment processes (solution, direct aging, and solution-aging), resulting in varying degrees of increased HE susceptibility. Specifically, after solution treatment, the complete elimination of cellular structure and the growth of grains concurrently increased hydrogen diffusion coefficient of the steel. However, its lower proportion of E3 boundaries and higher proportion of E11 boundaries played an advantageous role that lead to a marginal increase in the HE susceptibility. In contrast, direct aging and solution-aging treatments enhance the HE susceptibility significantly, which is primarily related to the decomposition of the cellular structure and reversible hydrogen trapping and precipitation strengthening effects of the newly formed Ni3(Ti, Mo) precipitates. Compared with the solution-aging treatment, the direct aging treatment results in the formation of a localized austenite aggregation zone near the molten pool boundaries, which promotes the initiation of hydrogen-assisted cracking and leads to a higher HE susceptibility.

Automated summary

The effects of heat treatment on the hydrogen embrittlement susceptibility of selective laser melted 18Ni300 maraging steel were investigated. The results showed that heat treatment could change the microstructure of the steel and lead to an increase in hydrogen embrittlement susceptibility. Solution treatment eliminated the cellular structure and increased the hydrogen diffusion coefficient, while the changes in interface proportions had little effect on the susceptibility. Direct aging and solution-aging treatments significantly enhanced the hydrogen embrittlement susceptibility due to the decomposition of the cellular structure and the effects of new precipitates.