拉伸及超声冲击处理塑性预变形后奥氏体不锈钢的氢脆机制

Hydrogen embrittlement (HE) is one of the major causes for the failures of metal structures using in hydrogen-containing environments, thus it is of great significance to study the HE of metals as well as its factors, and to devolve the methods of suppression of HE. Austenitic stainless steels (ASS) are the preferred materials for the manufacture of structures using in hydrogen-containing environments. However, controversial results have been found concerning the effect of plastic pre-deformation on HE susceptibility of ASS, especially the unstable ASS. In order to clarify the HE mechanisms as well as the hydrogen transport characteristics in the pre-deformed ASS, this project will investigate the HE of ASS with different stability after pre-deformation induced by tension and ultrasonic impact treatments (UIT). By investigating the HE susceptibility of ASS with varying hydrogen concentration and tension pre-deformation degree, the combined effect of hydrogen concentration and pre-existing α' martensite induced by the tension pre-deformation on HE mechanisms of the ASS will be revealed, the effect of pre-deformation and α' martensite on diffusivity and solubility of hydrogen in the steels will be also determined, the obtained results may helpful to understand the reason for the controversial results; By investigating the HE mechanisms and hydrogen transport characteristics of ASS after UIT with various process parameters, the effect of surface modifications induced by the treatments on HE mechanisms will be clarified, and the results showing whether the UIT is a method of suppression of HE of ASS will be obtained.

氢脆(HE)是引起临氢金属结构失效的主要原因之一，研究金属的HE及其影响因素，探寻抑制金属HE的方法，具有重要意义。奥氏体不锈钢（ASS）是制造临氢金属结构的优选材料，然而，在塑性预变形对ASS特别是不稳定ASS后续HE敏感性的影响方面，不同学者得到的研究结果不一致。为了澄清塑性预变形后ASS的HE机制与氢传输特性，本项目针对不同稳定性的ASS分别在拉伸和超声冲击处理（UIT）两种预变形后的HE，通过测试钢在不同氢浓度水平及拉伸预应变程度下的HE敏感性及氢传输特性，揭示氢浓度水平与α'马氏体含量综合影响下的钢HE机制，分析预应变及α'对钢中氢传输参数的影响，以澄清不同学者在此方面获得不同结果的原因；通过考察不同UIT工艺参数处理后的钢的HE敏感性和氢传输特性，揭示UIT引起的表层性状改变对钢HE机制的影响，探寻UIT在怎样的工艺参数或表面性状下具有抑制HE的作用。

氢脆(HE)是引起临氢金属结构失效的主要原因之一，研究金属HE及影响因素，具有重要意义。奥氏体不锈钢（ASS）是制造临氢金属结构的优选材料，但在加工制造过程中，不稳定ASS不可避免会经受塑性预变形，发生γ奥氏体向α'马氏体的相变。为了澄清塑性预变形后ASS的HE机制与氢传输特性，本项目针对不稳定ASS，基于一系列试验和理论分析计算手段，得到以下结论：1）α'虽在本质上HE敏感性远高于γ，但预应变诱导α'增加不稳定ASS的HE敏感性是因为其作为氢扩散高速通道增加了进入钢中的氢含量，大量氢位于靠近α'的γ中，使γ脆化导致了钢表现出高的HE敏感性；2）建立了预应变量-α'含量-氢传输参数（扩散系数与溶解度）之间的定量描述关系，该关系对FCC+BCC双相钢具有普适性；3）建立了应力及应变诱导α′相变协同作用下的氢扩散模型，开展了氢在受载304L钢裂纹尖端的氢扩散数值计算，裂尖变形诱导的α′相变不仅能够加速氢扩散，也能够提高氢富集水平，氢浓度在靠近α′的γ处最高，解释了不稳定ASS具有较高HE敏感性的原因；4）对预应变后ASS进行短时热处理，可降低预应变钢的HE敏感性，这是因为短时热处理可导致α′向γ回复，降低了钢中α′含量，使钢的HE抗性回复。但是，对热处理后钢进行预应变，将显著增加钢的HE，即使热处理时间很短，如焊接时，塑性应变较小，小于2%。这是因为这样的处理顺序比起单独预应变或敏化处理更能够显著导致晶界α′相变，因而更加促进沿晶断裂发生，导致钢的HE抗性显著降低，甚至低于碳钢。5）建立了描述裂纹尖端断裂过程区氢浓度富集水平及裂纹扩展速度的定量描述方程，该方程能够有效预测包括ASS在内的金属材料在含氢条件下的氢致裂纹扩展速度；6）基于内聚力模型（Cohesive Zone Modeling）和氢致键合力降低机制，并考虑多种陷阱（位错和晶界）对氢扩散和氢浓度分布的影响，通过耦合的扩散、陷阱、变形和氢致损伤有限元程序，给出了金属材料氢致裂纹形核的有限元预测方法。