A516碳鋼銲道在含H2S環境中之腐蝕破裂研究

Corrosion Cracking Behavior of A516 Steel Weld in Wet Hydrogen Sulfide Environment

本研究旨在探討A516碳鋼經弧銲後，銲道金屬在潮濕硫化氫環境中之腐蝕破裂性質。實驗包括金相組織觀察、硬度測試、及慢應變速率拉伸試驗。A516碳鋼分別進行15, 30, 45, 60KJ/cm四組不同入熱量之潛弧銲接。在空氣中進行機械性質測試的結果顯示，銲道金屬之抗拉強度隨著入熱量的增加有下降的趨勢，且上層試片之強度有高於中、下層之傾向；而均勻延伸率的變化則較不規則。在含飽合硫化氫之NACE溶夜中進行慢應變速率拉伸試驗中發現，若以延伸率比值來評佔腐蝕破裂裂敏感性時，上層試片常具有最高之腐蝕破裂敏感性。試片破斷面呈脆性劈裂的型態，顯示氫脆的特徵。而橫截面金相則顯示上層銲道柱狀晶組織中的晶粒界肥粒鐵是發生硫化物應力腐蝕破裂（SSCC）之敏感區域。

The corrosion cracking behavior of A516 carbon steel weld, by submerged arc welding. in hydrogen sulfide containing NACE solution was investigated. Submerged arc welding with beat inputs of 15, 30, 45 and 60 KJ/cm were applied. The slow strain rate testing (SSRT) technique was used to evaluate the corrosion cracking susceptibility. The strength of the weld in air was found to vary inversely proportional to the welding heat input. A significant reduction of the ductility, based on the elongation ration, was observed for all the specimens tested in hydrogen sulfide containing solutions. The results also indicated that the specimens made from the top of welds were most susceptible to corrosion cracking as compared to those prepared from the middle and the bottom of the welds. Cleavage type of fracture was observed, revealing the empbrittlement effect of hydrogen. Primary or secondary cracks were also observed in the welds propagating along the grain boundary ferrite indicating the relative high resistance of the accicular ferrite to sulfide stress corrosion cracking (SSCC).