鈮添加與熱處理程序對硼系超高強度鋼之氫脆性質研究

15B30為硼系超高強度鋼，在麻田散鐵態時其強度達2000MPa，由於其高強度之特性，在結構鋼及汽車鋼板應用上有出色的表現。然而超高強度鋼之缺點為易受到氫脆效應的影響，在實際應用上此因素可能會造成無法預測之破壞。本實驗研究目標為建立氫脆破壞之評估方法及抗氫脆破壞之方法，藉由微合金元素鈮的添加與熱處理程序來達成。利用化學充氫及拉伸試驗發現15B30在麻田散鐵態下其抗氫脆能力最差，最大抗拉強度損失達70%，並且可以發現破斷面有明顯之沿晶破壞組織；將15B30經過回火200℃、300℃，及400℃處理後發現200℃有最佳抗氫脆能力，主要原因為ε碳化物在麻田散鐵板條內部析出，提供額外氫捕集位置。回火300℃及400℃時雪明碳鐵在板條間及先前沃斯田鐵晶界析出，此種界面之氫捕集位置使得氫脆破壞現象加劇，使得抗氫脆能力較回火200℃時差。添加鈮元素之改良型15B30Nb，內部會有(Nb,Ti)(CN)及NbC析出，對材料有晶粒細化之作用，此效應在回火狀態充氫拉伸發現有良好的抗氫脆能力。而從定應力拉伸試驗發現鈮添加後晶粒細化之15B30Nb經過較久的時間後才斷裂，顯示有較佳之抗氫脆能力。

關鍵字

氫脆；超高強度鋼；回火麻田散鐵；碳化鈮

並列摘要

15B30 steel, an ultra-high strength boron steel, has 2000MPa ultra-high tensile strength in martensitic state. Due to its high strength property, 15B30 steel is best used in structural steel and automotive plate. However, ultra-high strength steel is prone to hydrogen embrittlement in practical usage, which will lead to severe unpredictable fracture. The aims of this research are to build up an evaluation method of hydrogen embrittlement and find the effects niobium-additive and heat treatment on the hydrogen embrittlement of 15B30 steel. After chemical hydrogen charging, the as-quenched 15B30 exhibits the worst resistance of hydrogen embrittlement. Its percentage loss of UTS after hydrogen charging is about 70%, and the fractography is intergranular fracture. Through tempering processes in different temperatures, it is found that 200℃ tempering processing is effective to resist the hydrogen embrittlemet. This feature is mainly ascribed to the ε carbide precipitates in the martensite lath, which can provide additional hydrogen trapping site. The cementite will precipitate along martensite lath interface and prior austenite grain boundary during the tempering at 300℃ and 400℃. This type of hydrogen trapping sites lead to a weaker resistance to hydrogen embrittlement. Niobium-added 15B30, namely the 15B30Nb steel, can have the refined grains due to the existence of (Nb,Ti)(CN) and NbC precipitates. These refined grains could improve noticeably the hydrogen embrittlement resistance in the tempering state. Constant load test shows that the hydrogen pre-charged 15B30Nb steel could sustain a longer fracture time, which also reveals that the refined grains have better hydrogen embrittlement resistance.

並列關鍵字

hydrogen embrittlement ； ultra-high strength steel ； tempered martensite ； niobium carbide

參考文獻

2. Stormvinter, A., et al., Effect of carbon content on variant pairing of martensite in Fe–C alloys. Acta Materialia, 2012. 60(20): p. 7265-7274.

4. Thomas, G., Retained austenite and tempered martensite embrittlement. Metallurgical Transactions A, 1978. 9(3): p. 439-450.

5. Wells, M.G.H., An electron transmission study of the tempering of martensite in an Fe-Ni-C alloy. Acta Metallurgica, 1964. 12(4): p. 389-399.

8. Sarikaya, M., A.K. Jhingan, and G. Thomas, Retained austenite and tempered martensite embrittlement in medium carbon steels. Metallurgical Transactions A, 1983. 14(6): p. 1121-1133.

10. Birkle, A., et al., A metallographic investigation of the factors affecting the notch toughness of maraging steels. 1964, DTIC Document.

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鈮添加與熱處理程序對硼系超高強度鋼之氫脆性質研究

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