含銅焠火-回火型麻田散鐵鋼之熱脫氫行為

Abstract

麻田散鐵在淬火回火製程中析出的銅顆粒擁有二次硬化的效果。然而，僅有少數的研究論及銅析出顆粒在鋼鐵中的吸氫能力.這份工作目標在於指出麻田散鐵中析出的銅顆粒具備氫陷阱的效果，並且使材料擁有抗氫脆的能力。為了與傳統淬火回火麻田散鐵比較，S690Q等級之海洋用鋼亦使用於研究中。研究中使用光學顯微鏡，掃描式電子顯微鏡，與穿透式電子顯微鏡來完成顯微結構的觀察。試片利用陰極電化學方式充氫後置於管型爐內加熱，過程中利用氣相層析儀量測其熱脫氫行為。材料的抗氫脆能力使用開槽之拉伸試片進行慢速率拉伸檢測其抗氫脆能力。在傳統淬火回火鋼中，大量的氫儲存於淬火下產生之差排與晶界，在回火後氫含量隨差排與晶界減少而減少，同時回火條件中產生之雪明碳鐵並沒有顯著的吸氫能力。而在含銅淬火回火鋼中，回火過程中析出之銅顆粒具備了明顯的氫陷阱的效果。使用Kissinger與 McNabb-Foster方法分析後得知，銅顆粒氫陷阱的熱脫活化能介於35至40 kJ/mol 之間，相較於差排與晶界能夠更有效的限制氫在材料中的擴散。在慢速率拉伸試驗中，含銅回火淬火鋼在回火 540度到600度之間析出高密度銅顆粒產生的氫陷阱明顯延緩了拉伸過程中氫往應力集中處擴散的現象，有效的提升材料抗氫脆能力。總結來說，含銅顆粒析出之淬火回火鋼具備相當好的吸氫能力，成為設計抗氫脆能力鋼種的冶金方法。

Precipitation of copper in martensitic steel after tempering is known to trigger secondary hardening effect in quenched-and-tempered (Q&T) martensitic steel. However, there have been few studies conducted to the ability of copper to trap hydrogen in steels. The current work aims at characterizing the effects of copper on hydrogen desorption and resistance to hydrogen embrittlement in Q&T martensitic steels. Moreover, in order to compare with conventional Q&T steel, S690Q offshore steel was also studied. In this research, microstructure was investigated by using optical microscope, scanning electron microscope, and transmission electron microscope. Specimens electrochemically charged with hydrogen was measured in the house-constructed thermal desorption spectroscopy (TDS), and hydrogen desorption models were utilized to analyze experiment results. Resistance to hydrogen embrittlement was finally tested via the notched slow strain rate tensile testing. In conventional Q&T steel, ability to store hydrogen is high in as-quenched steel due to high dislocation density and grain boundary and it will degrade after tempering. Cementite particles, formed by tempering in conventional Q&T steel, have weak ability to trap hydrogen. However, precipitation of copper can enhance the hydrogen trapping in the copper-containing Q&T steel. Based on the analyses by Kissinger method and McNabb-Foster method, the binding energy of copper particle was estimated to be 35 to 40 kJ/mol. Strong enhancement in hydrogen trapping was observed when the steel was tempered at 540 oC or 600 oC. This is consistent with the fact that high-density copper particles were also observed in steels under these tempering conditions. In SSRT tests, steel with copper precipitation shows better resistance to hydrogen embrittlement. In conclusion, precipitation of copper is a metallurgical approach in designing a strong and tough Q&T steel with high resistance to hydrogen embrittlement.