目的：研究预先存在于试样中的氢对材料力学性能的影响。方法对固溶态和三种时效态18Ni马氏体时效钢，采用双电解槽装置测量了其氢扩散系数，用热分析法获得了材料的氢扩散激活能。采用慢应变速率拉伸法评估了在预充氢后镀镉密封试样的力学性能，并由此评估它们的氢脆敏感性。结果固溶态试样的氢扩散系数最大，为1.40×10?8 cm2/s；对时效态试样，当时效温度分别为465、490、530℃时，氢扩散系数分别为6.23×10?9、5.52×10?9、2.84×10?9 cm2/s，即随时效温度升高，扩散系数降低。而扩散激活能正好相反，固溶态的最小，其他的依次逐渐升高。四种试样均显示出氢脆敏感性，且随着预充氢电流密度升高而增大。T465和T490的氢脆敏感性均大于58%，T530的氢脆敏感性小于40%。四种试样的断口形貌均表现为由中心起裂，向周围呈放射状扩展。中心起裂源处为典型的沿晶开裂，扩展区为准解理开裂。结论过时效态样品的抗氢脆性能最好。预先存在于试样中的氢在拉伸过程中向中心富集，造成中心沿晶开裂，与动态充氢拉伸断口相反。
ABSTRACT:Objective To study the effect of pre-existed hydrogen in specimen on the mechanical properties.Methods For a type of solution-treated and three types of heat-treated 18Ni maraging steels, electrochemical permeation was employed to de-termine effective hydrogen diffusion coefficient (Def); thermal desorption analysis (TDA) was carried out to assess activity en-ergies (Ea); slow strain rate tensile tests were performed to characterize the mechanical properties and further evaluate the hy-drogen embrittlement (HE) susceptibility of pre-charged and cadmium coated specimens in comparison of uncharged specimens. Results The results showed thatDef of the solution-treated specimen was 1.40×10?8cm2/s, which was the largest among four specimens.Def of three heat-treated specimens gradually decreased with the rise of aging temperature, which were 6.23×10?9 cm2/s for 465℃, 5.52×10?9 cm2/s for 490℃ and 2.84×10?9cm2/s for 530℃ respectively; whereas,Ea gradually rose. Four specimens all exhibited HE susceptibility, which increased with the rise of charging current density. The HE susceptibility in-dexes for T465 and T490 were both higher than 58%, while that for T530 was smaller than 40%. In the fracture morphology of the four specimens, cracks initiated from the centre and radiated to surrounding. Centre crack source was a typical intergranular feature, while the extension area was quasi-cleavage cracking.Conclusion The hydrogen embrittlement of overaging samples is the best. The pre-existed hydrogen in the sample gathers in the center during tensile test, which causes intergranular crack in the center and reverse to dynamic hydrogen charging tensile fracture.
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