沉淀強化奧氏體不銹鋼焊件氫脆研究
發(fā)布時間：2018-12-08 10:18
【摘要】：沉淀強化型奧氏體不銹鋼由于同時具有奧氏體組織優(yōu)良的抗氫脆性能和沉淀相強化處理后較高的強度,被視為未來臨氫工作材料的最佳選擇之一。在實際工程應用中,為了組裝成大的完整的工件,焊接往往是不可避免的。焊接過程會造成母材和焊縫微觀結(jié)構(gòu)的差異,并且這些差異難以通過后續(xù)的熱處理或其它方法完全消除。焊件微觀結(jié)構(gòu)的不均一又會導致焊件力學性能的差異。同時,在氫環(huán)境服役過程中,焊件的微結(jié)構(gòu)的不均一還會引起氫在焊件中擴散和分布的不平衡,進而出現(xiàn)氫致微裂紋萌生及擴展的差異。沉淀強化奧氏體不銹鋼作為在臨氫環(huán)境下服役的材料,由于其發(fā)展時間較短,因此關(guān)于其氫脆的研究相對較少,針對其焊件的氫脆研究更少,而焊縫又往往是整個焊件的薄弱區(qū)。為了確保沉淀強化奧氏體不銹鋼焊件在臨氫工程上的安全應用并促進其臨氫服役性能的進一步優(yōu)化,針對沉淀強化奧氏體不銹鋼焊件的氫脆研究是必須進行的。在這個前提下,我們展開了以下工作： 首先,我們通過金相分析、無載荷充氫、動態(tài)充氫橫載荷拉伸實驗對沉淀強化奧氏體鋼電子束焊件的氫損傷、氫擴散系數(shù)及氫服役安全性進行了評估。結(jié)果發(fā)現(xiàn)：整個焊件分為母材區(qū)和焊縫區(qū),母材區(qū)為平均晶粒尺寸40-50μmm的典型奧氏體組織,有少量退火攣晶：焊縫區(qū)寬度為2mm左右,在母材區(qū)和焊縫區(qū)的交界處不存在明顯的粗晶熱影響區(qū),焊縫區(qū)由連接母材的大尺寸柱狀晶區(qū)和處在焊縫中心的窄的等軸晶區(qū)組成；焊縫等軸晶區(qū)是整個焊件的強度薄弱區(qū),同時也是整個焊件的氫脆最敏感區(qū)；焊件氫致滯后斷裂門檻應力σth/σb隨著截止時間tc(hr)的增加呈指數(shù)降低,即：氫在焊縫中的表觀擴散系數(shù)估值為：如果沉淀強化奧氏體不銹鋼焊件作為儲氫容器來使用的話,在我們的測試條件下,容器40年不發(fā)生氫致失效的門檻應力估算值為而要保證氫在40年內(nèi)不從容器中滲漏出去,則容器壁厚需大于3mm。 在以上基礎(chǔ)上,我們結(jié)合焊件微結(jié)構(gòu)透射電子顯微鏡(TEM)表征、動態(tài)充氫恒載荷斷口掃描電子顯微鏡(SEM)觀察和透射電子顯微鏡(TEM)原位拉伸進一步深入系統(tǒng)地分析了焊件微結(jié)構(gòu)不均一對其氫脆的影響,結(jié)果表明：母材區(qū)中位錯極少,有少量的晶界及晶內(nèi)大尺寸沉淀相,焊縫中無論是柱狀晶區(qū)還是等軸晶區(qū),都存在高密度的彎曲位錯,同時存在大量的被高密度位錯環(huán)繞的大尺寸沉淀相作為氫陷阱和微裂紋萌生位置：整個焊件中的時效沉淀強化相均為γ'Ni3(Al,Ti)相,焊縫中丫'相尺寸是母材中的3倍大,且分布稀疏,造成焊縫中γ'相強化作用下降,變形過程中,母材中的位錯平面滑移并切過丫'相,焊縫中彎曲位錯環(huán)繞丫'相形成位錯環(huán),導致位錯纏結(jié)并成為氫陷阱,在變形較大的情況下,焊縫中丫'相也成為微裂紋萌生位置；最終導致焊件氫致滯后斷裂機理隨外加應力的變化而變化：當外加應力較高時,脆性穿晶斷裂占主導地位,隨著外加應力的降低,脆性沿晶斷裂的比例逐漸升高。
[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
【學位授予單位】：北京科技大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TG441.7
本文編號：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
【學位授予單位】：北京科技大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TG441.7
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