沉淀硬化马氏体不锈钢中氢陷阱作用机制研究

沉淀硬化马氏体不锈钢的氢脆是其安全服役的瓶颈问题，通过组织结构优化突出氢陷阱作用，获得优异抗氢脆性能，是目前抗氢脆高强钢研发热点。本申请针对分别以富Cu相、NiAl相为沉淀硬化相的17-4PH、PH13-8马氏体不锈钢，通过研究时效中富Cu相/基体界面的吸氢行为，弄清界面结构对其氢捕获行为的影响；对比同为共格析出的bcc-Cu和NiAl相的吸氢行为，明确析出相/基体界面作为氢陷阱的关键控制因素；利用NiAl相尺寸、界面结构稳定的特点，研究时效中马氏体组织结构演化对片层间界氢捕获能力的影响，揭示调幅分解、逆转变奥氏体的作用机制；定量化对比基体组织稳定富Cu相结构转变、NiAl相稳定基体结构发生演化的两个时效过程中氢脆敏感性、裂纹萌生扩展的特征，弄清析出相、马氏体组织在氢脆中的作用权重，从而为优化时效工艺、改善组织结构来强化氢陷阱的作用、实现抗氢脆沉淀硬化马氏体不锈钢的研发目标提供理论支撑。

High strength steels are becoming increasingly important in aerospace, power generation, shipbuilding, and automotive industries. Maraging steels, combining a martensite matrix with nanoprecipitates, are a class of high-strength materials with the potential for matching these demands. However, the susceptibility of steels to hydrogen embrittlement (HE) increases with their strength and with the complexity of their microstructures. In this proposal, HE of two kinds of the precipitation-hardened martensitic stainless steel (PH stainless steel), i.e., 17-4PH and PH13-8, are investigated, which are hardening by Cu-rich precipitates and NiAl precipitates, respectively. During aging process or in service at high temperature, Cu-rich precipitates may experience bcc-9R-fcc microstructure transformation, while the size and coherence relation to matrix of NiAl precipitates do not change even aged at 620oC for 4 hours. Formation of reverted austenite and spinodal decomposition of the martensite phase into Fe-rich phase and Cr-enriched phase happen when the aging temperature and time increase. Characterization of the microstructural evolution will be carried out through TEM observation. Using lattice-resolved conductivity mapping by C-AFM and first-principles calculations, the effect of aging condition on hydrogen traps, i.e., precipitates and interfaces between martensite lathes and reverted austenite boundary is analyzed. The influence of these microstructural evolution on HE of these two steels is evaluated by means of slow strain rate test and fatigue test. Observation by three-dimensional atom probe (3DAP) will be performed to characterize the hydrogen trap behavior on interface between precipitate and matrix, and the effect of microstructure of the interface on hydrogen adsorption on precipitate is studied through energy analysis by first-principles calculation. Optimum aging process is explored based on understanding the mechanism of hydrogen trapping in PH stainless steel by precipitates and martensite laths, in order to improve the resistance of hydrogen embrittlement of PH stainless steel.