预充氢马氏体时效钢的氢脆性能研究

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)_ cm~2/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) cm~2/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。

Study on Hydrogen Embrittlement for Pre-charged Maraging Steel

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.