MS X70酸性環(huán)境用管線鋼焊接接頭氫致開裂敏感性及氫捕獲效率研究

MS X70酸性環(huán)境用管線鋼焊接接頭氫致開裂敏感性及氫捕獲效率研究Hydrogen-induced cracking susceptibility and hydrogen trapping efficiency of the welded MS X70 pipeline steel in H2S environment

依據(jù)NACE TM0284-2011標準對MS X70管線鋼母材及其焊接接頭氫致開裂（HIC）敏感性進行了評估；運用金相顯微鏡（OM），場發(fā)射掃描電鏡（FE-SEM）和電子背散射衍射（EBSD）對其顯微組織、HIC裂紋及周圍的晶界結構進行了觀察和分析，并通過計算滲透通量（J∞L）和氫有效擴散系數(shù)（Deff）對母材及焊接接頭的氫捕獲效率進行了比較研究。結果表明：MS X70管線鋼母材及其焊接接頭的HIC敏感性均不能達到歐標要求，且焊接接頭比母材具有更高的HIC敏感性。焊接接頭較高的HIC敏感性主要歸結于：（1）以條狀貝氏體為主的焊縫組織對氫原子的捕獲效率高于母材，（2）焊接接頭中較多作為氫通道的小角度晶界可通過提高大角度晶界氫捕獲效率從而增加其裂紋敏感率，（3）焊接接頭中較少量低能CSL晶界和Σ13b、Σ29b重位晶界降低了大角度晶界裂紋擴展抗力從而使其具有更高的HIC敏感性。

Hydrogen-induced cracking (HIC) susceptibility of welded MS X70 pipeline steels was evaluated in NACE “A” solution at room temperature according to the NACE TM 0284-2011 standard. The metallurgical microscope,field emission scanning electron microscopy(FE-SEM),energy dispersive spectroscopy(EDS) and electron backscattered diffraction(EBSD) were employed to study the microstructure and HIC cracks in the MS X70 base steel and its welded joint. The hydrogen trapping efficiency were also investigated by measuring the permeability(J∞L) and the effective hydrogen diffusivity (Deff). It has been found that both base metal and welded joint were highly susceptible to HIC and the later steel sample was more vulnerable than the former. This higher susceptibility could be primarily attributed to the following effects : (1)the higher hydrogen trapping efficiency of bainitic lath microstructure in the welded joint; (2)the more low angle grain boundary as diffusion path for hydrogen in the welded joint also made it easier to crack by improving the trapping efficiency of high angle grain boundary; (3)the less amount of CSL grain boundary and Σ13b、Σ29b lead to higher HIC susceptibility by decreasing the resistance to crack of high angle grain boundary.

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