沉淀强化奥氏体不锈钢焊件氢脆研究
发布时间：2018-12-08 10:18
【摘要】：沉淀强化型奥氏体不锈钢由于同时具有奥氏体组织优良的抗氢脆性能和沉淀相强化处理后较高的强度,被视为未来临氢工作材料的最佳选择之一。在实际工程应用中,为了组装成大的完整的工件,焊接往往是不可避免的。焊接过程会造成母材和焊缝微观结构的差异,并且这些差异难以通过后续的热处理或其它方法完全消除。焊件微观结构的不均一又会导致焊件力学性能的差异。同时,在氢环境服役过程中,焊件的微结构的不均一还会引起氢在焊件中扩散和分布的不平衡,进而出现氢致微裂纹萌生及扩展的差异。沉淀强化奥氏体不锈钢作为在临氢环境下服役的材料,由于其发展时间较短,因此关于其氢脆的研究相对较少,针对其焊件的氢脆研究更少,而焊缝又往往是整个焊件的薄弱区。为了确保沉淀强化奥氏体不锈钢焊件在临氢工程上的安全应用并促进其临氢服役性能的进一步优化,针对沉淀强化奥氏体不锈钢焊件的氢脆研究是必须进行的。在这个前提下,我们展开了以下工作： 首先,我们通过金相分析、无载荷充氢、动态充氢横载荷拉伸实验对沉淀强化奥氏体钢电子束焊件的氢损伤、氢扩散系数及氢服役安全性进行了评估。结果发现：整个焊件分为母材区和焊缝区,母材区为平均晶粒尺寸40-50μmm的典型奥氏体组织,有少量退火挛晶：焊缝区宽度为2mm左右,在母材区和焊缝区的交界处不存在明显的粗晶热影响区,焊缝区由连接母材的大尺寸柱状晶区和处在焊缝中心的窄的等轴晶区组成；焊缝等轴晶区是整个焊件的强度薄弱区,同时也是整个焊件的氢脆最敏感区；焊件氢致滞后断裂门槛应力σth/σb随着截止时间tc(hr)的增加呈指数降低,即：氢在焊缝中的表观扩散系数估值为：如果沉淀强化奥氏体不锈钢焊件作为储氢容器来使用的话,在我们的测试条件下,容器40年不发生氢致失效的门槛应力估算值为而要保证氢在40年内不从容器中渗漏出去,则容器壁厚需大于3mm。 在以上基础上,我们结合焊件微结构透射电子显微镜(TEM)表征、动态充氢恒载荷断口扫描电子显微镜(SEM)观察和透射电子显微镜(TEM)原位拉伸进一步深入系统地分析了焊件微结构不均一对其氢脆的影响,结果表明：母材区中位错极少,有少量的晶界及晶内大尺寸沉淀相,焊缝中无论是柱状晶区还是等轴晶区,都存在高密度的弯曲位错,同时存在大量的被高密度位错环绕的大尺寸沉淀相作为氢陷阱和微裂纹萌生位置：整个焊件中的时效沉淀强化相均为γ'Ni3(Al,Ti)相,焊缝中丫'相尺寸是母材中的3倍大,且分布稀疏,造成焊缝中γ'相强化作用下降,变形过程中,母材中的位错平面滑移并切过丫'相,焊缝中弯曲位错环绕丫'相形成位错环,导致位错缠结并成为氢陷阱,在变形较大的情况下,焊缝中丫'相也成为微裂纹萌生位置；最终导致焊件氢致滞后断裂机理随外加应力的变化而变化：当外加应力较高时,脆性穿晶断裂占主导地位,随着外加应力的降低,脆性沿晶断裂的比例逐渐升高。
[Abstract]:The precipitation-enhanced austenitic stainless steel is considered to be one of the best choice for future hydrogen-working materials due to its high strength at the same time with excellent anti-hydrogen embrittlement resistance and precipitation phase-enhanced treatment at the same time. In practical engineering applications, welding is often inevitable in order to assemble a large, complete workpiece. the welding process may result in a difference in the microstructure of the parent and the weld, and these differences are difficult to be completely eliminated by subsequent heat treatment or other methods. The non-uniformity of the microstructure of the welded parts can also lead to the difference of the mechanical properties of the welded parts. At the same time, in the process of hydrogen environment service, the non-uniformity of the microstructure of the welding part can also cause the non-equilibrium of the diffusion and distribution of hydrogen in the welding piece, and then the difference of the initiation and expansion of the hydrogen-induced micro-crack. Precipitation-reinforced austenitic stainless steel is used as a material for service in the near-hydrogen environment, because its development time is short, the research on its hydrogen embrittlement is relatively small, and the hydrogen embrittlement of the welded part is less, and the welding seam is often the weak area of the whole welding piece. In order to ensure the safe application of the precipitation-enhanced austenitic stainless steel weld to the hydrogen engineering and to promote the further optimization of its hydrogen service performance, it is necessary to study the hydrogen embrittlement of the precipitation-enhanced austenitic stainless steel weld. In this context, we have undertaken the following: First of all, we evaluated the hydrogen damage, the hydrogen diffusion coefficient and the hydrogen service safety of the precipitation-reinforced austenitic steel electron beam welding by gold-phase analysis, no-load hydrogen-filled and dynamic hydrogen-filled transverse-load tensile test. The results show that the whole welding part is divided into the main material area and the weld area, and the mother material area is a typical austenite structure with average grain size of 40-50 & mu; m, with a small amount of annealed columnar crystal: the width of the weld area is about 2mm, and there is no obvious coarse-crystal heat effect at the junction of the mother material area and the weld area. The weld zone is composed of a large-size columnar crystal region connecting the mother material and a narrow equiaxed crystal region at the center of the welding line, the axial crystal region of the weld line is the weak region of the strength of the whole welding piece, and the welding seam region is also the most sensitive to the hydrogen embrittlement of the whole welding piece The zone; the weld hydrogen-induced hysteresis fracture threshold stress (th/ b) decreases exponentially with the increase of the cut-off time tc (hr), i.e. the apparent diffusion coefficient of hydrogen in the weld is estimated to be: if the precipitation-reinforced austenitic stainless steel weld is used as a hydrogen storage vessel, in our test conditions The vessel wall thickness shall be greater than 3m in order to ensure that the hydrogen does not leak out of the vessel within 40 years without the threshold stress estimate for hydrogen-induced failure in the vessel for 40 years. m. On the basis of the above, we have a microstructure transmission electron microscope (TEM) of the welded parts The effects of non-uniform microstructure of the welded parts on the hydrogen embrittlement of the welded parts were analyzed by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in situ, and the results showed that in the mother material area, At the same time, there is a large number of large-size precipitates surrounded by high-density dislocations as hydrogen traps and micro-cracks. Location of raw material: the aging and precipitation strengthening in the whole welding piece The phase is 1 'Ni3 (Al, Ti) phase, and the welding is carried out. The size of the joint in the seam is three times larger than that of the parent material, and the distribution is sparse, resulting in In the process of deformation, the dislocation plane in the mother material is slip and cut a' 'phase, bend in the weld the dislocation loop is formed in the wrong-around ma' phase, which causes the dislocation to be entangled and becomes a hydrogen trap, and in the case of large deformation, the welding When the applied stress is high, the brittle-penetrating fracture is dominant, with the decrease of the applied stress, the ratio of the brittle fracture to the crystal fracture is
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG441.7
本文编号：2368177
[Abstract]:The precipitation-enhanced austenitic stainless steel is considered to be one of the best choice for future hydrogen-working materials due to its high strength at the same time with excellent anti-hydrogen embrittlement resistance and precipitation phase-enhanced treatment at the same time. In practical engineering applications, welding is often inevitable in order to assemble a large, complete workpiece. the welding process may result in a difference in the microstructure of the parent and the weld, and these differences are difficult to be completely eliminated by subsequent heat treatment or other methods. The non-uniformity of the microstructure of the welded parts can also lead to the difference of the mechanical properties of the welded parts. At the same time, in the process of hydrogen environment service, the non-uniformity of the microstructure of the welding part can also cause the non-equilibrium of the diffusion and distribution of hydrogen in the welding piece, and then the difference of the initiation and expansion of the hydrogen-induced micro-crack. Precipitation-reinforced austenitic stainless steel is used as a material for service in the near-hydrogen environment, because its development time is short, the research on its hydrogen embrittlement is relatively small, and the hydrogen embrittlement of the welded part is less, and the welding seam is often the weak area of the whole welding piece. In order to ensure the safe application of the precipitation-enhanced austenitic stainless steel weld to the hydrogen engineering and to promote the further optimization of its hydrogen service performance, it is necessary to study the hydrogen embrittlement of the precipitation-enhanced austenitic stainless steel weld. In this context, we have undertaken the following: First of all, we evaluated the hydrogen damage, the hydrogen diffusion coefficient and the hydrogen service safety of the precipitation-reinforced austenitic steel electron beam welding by gold-phase analysis, no-load hydrogen-filled and dynamic hydrogen-filled transverse-load tensile test. The results show that the whole welding part is divided into the main material area and the weld area, and the mother material area is a typical austenite structure with average grain size of 40-50 & mu; m, with a small amount of annealed columnar crystal: the width of the weld area is about 2mm, and there is no obvious coarse-crystal heat effect at the junction of the mother material area and the weld area. The weld zone is composed of a large-size columnar crystal region connecting the mother material and a narrow equiaxed crystal region at the center of the welding line, the axial crystal region of the weld line is the weak region of the strength of the whole welding piece, and the welding seam region is also the most sensitive to the hydrogen embrittlement of the whole welding piece The zone; the weld hydrogen-induced hysteresis fracture threshold stress (th/ b) decreases exponentially with the increase of the cut-off time tc (hr), i.e. the apparent diffusion coefficient of hydrogen in the weld is estimated to be: if the precipitation-reinforced austenitic stainless steel weld is used as a hydrogen storage vessel, in our test conditions The vessel wall thickness shall be greater than 3m in order to ensure that the hydrogen does not leak out of the vessel within 40 years without the threshold stress estimate for hydrogen-induced failure in the vessel for 40 years. m. On the basis of the above, we have a microstructure transmission electron microscope (TEM) of the welded parts The effects of non-uniform microstructure of the welded parts on the hydrogen embrittlement of the welded parts were analyzed by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in situ, and the results showed that in the mother material area, At the same time, there is a large number of large-size precipitates surrounded by high-density dislocations as hydrogen traps and micro-cracks. Location of raw material: the aging and precipitation strengthening in the whole welding piece The phase is 1 'Ni3 (Al, Ti) phase, and the welding is carried out. The size of the joint in the seam is three times larger than that of the parent material, and the distribution is sparse, resulting in In the process of deformation, the dislocation plane in the mother material is slip and cut a' 'phase, bend in the weld the dislocation loop is formed in the wrong-around ma' phase, which causes the dislocation to be entangled and becomes a hydrogen trap, and in the case of large deformation, the welding When the applied stress is high, the brittle-penetrating fracture is dominant, with the decrease of the applied stress, the ratio of the brittle fracture to the crystal fracture is
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG441.7
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