含鉬高強度管線用鋼研究

Study on Mo-bearing High-Strength Steels for Pipelines

李至隆(J. L. Lee) ； 謝榮淵(R. I Hsieh) ； 劉宏義(H. Y. Liou)

《鑛冶：中國鑛冶工程學會會刊》 37卷3期 (1993/09) Pp. 101-114

摘要

本文研究鉬（Mo）含量（0〜0.45 wt%）對鋼材之顯微組織及各項性質的影響，以做為高強度管線用鋼合金設計之參考。Mo添加可使晶粒細化，第二相的體積增加；且使第二相由波來鐵轉變成假性波來鐵及麻田散鐵，故造成連續形的降伏曲線。這些組織變化，使鋼材之抗拉強度隨Mo之增加而提高，降伏強強度則反而降低，且在0.3%Mo出現最低值。0.15%Mo鋼因晶粒細化，故韌性最佳；0.3%及0.45%Mo鋼則因含較多硬脆第二相，故韌性惡化。Mo的添加，因可減小Lüder strain，故可使鋼材避免製管時之強度損失。在銲接時，Mo會促進麻田散鐵－沃斯田鐵硬脆相的生成，而不利熱影響區韌性及冷裂敏裂性。Mo對抗氫引裂（HIC）性有兩方面的影響：（i）因促進麻田散鐵第二相，不利抗HIC性；（ii）因形成保護膜，有利抗HIC性，故抗HIC性以0 Mo及0.45%Mo鋼較佳。另外，加速鋼板冷卻速率，因可促進針狀肥粒鐵的形成，使得0.15%Mo鋼強度提高約7 kg/mm^2，且保持原有之韌性。添加Cu、Ni可以改善含Mo鋼之銲接性及抗HIC性，故可製出性質優良之低溫管線用鋼。

並列摘要

Five steels were prepared to study the specific effects of Mo contents on the microstructures and properties of line pipe steels. Mo addition is found to refine ferrite grains, increase the volume fraction of second phase and cause a transition of second phase from pearlite to pseudo pearlite and martensite, thereby resulting in a continuous yielding stress-strain curve. The tensile strength of steel increases, while yield strength decreases with increasing Mo contents due to the above microstructural modifications. 0.15%. Mo steel has the best toughness owing to its refined ferrite grain, whereas 0.45% Mo steel has the worst toughness because of the existence of large amount of martensite. The addition of Mo can prevent strength loss during pipe forming by decreaseing the Lüder strain of steels, but impair the HAZ toughnes, enhance cold cracking of steel welds and deteriorate the hydrogen-induced cracking (HIC) resistance by promoting hard second phase. Excessive Mo content can improve HIC resistance due to the formation of a passive film. The alloy design of high strength line pipe steel is proposed and discussed on the basis of the above experimental results.