高強度粉末合金鋼之衝擊韌性與疲勞強度之研究

Impact Toughness and Fatigue Properties of High-Strength Powder Metal Steels

林稟豪(Bing-Hao Lin)

指導教授 ： 吳明偉

國立虎尾科技大學/工程學院/材料科學與綠色能源工程研究所/碩士(2012年)

https://doi.org/10.6827/NFU.2012.00094

摘要

粉末合金鋼廣泛使用於汽機車等機械相關產業，但其抗拉強度通常與韌性往往成反比，因此要同時兼具高強度與高韌性相當不容易。為使粉末合金鋼能具備優異之動靜態機械性質，因此本研究初步先探討Mo、Cr、Ni等合金元素對衝擊韌性的影響，結果顯示在Fe-0.5C添加1.5wt%Mo會使粉末合金鋼之衝擊韌性降低，而添加Cr與Ni則會提升衝擊韌性。除了探討單一合金元素之外，本研究也深入探討含Ni粉末合金鋼以Fe-4Ni-0.5C添加Mo、Cr兩種元素之影響，結果顯示添加1.5wt%Mo會使降低粉末合金鋼之衝擊韌性，主要是因組織中會形成粗大的退化波來鐵，而添加1.5Cr-0.2Mo或3Cr-0.5Mo後則因Cr能使燒結頸部區形成高強韌性的富Ni麻田散鐵，因此不僅在抗拉強度大幅上升之同時不損害韌性，甚至使韌性更為提高。
在橫向破裂強度與疲勞性質方面，發現藉由添加Mo與Cr皆可有效改善含Ni粉末合金鋼之疲勞性質。因此本研究成功藉由合金設計研製出同時具有優異動靜態機械性質(抗拉強度、衝擊韌性與疲勞強度)之粉末合金鋼，如Fe-4Ni-3Cr-0.5Mo-0.5C，其在1250℃燒結且經回火後之抗拉強度達1323MPa、橫向破裂強度達2173MPa、疲勞強度達700MPa以上、衝擊能更達到38.9J，不僅強度獲得提升，且衝擊韌性也夠進一步增加，因此優異的混合組織使該合金鋼同時兼具高強度與高韌性之合金鋼。

關鍵字

粉末合金鋼 ； 衝擊韌性 ； 破壞 ； 橫向破裂強度 ； 疲勞強度

並列摘要

The impact toughness of powder metal steels is usually impaired by improving the tensile strength. The development of high-strength and hightoughness PM steels are thus very difficult. The effect of Mo, Cr and Ni on the impact toughness of powder metal steels was investigated in this study. The results showed that the Fe-0.5C steels was increased by Cr and Ni, but decreased by Mo. The effects of Mo and Cr on the toughness of the Fe-4Ni-0.5C steel was also examined. The results showed that the addition of 1.5wt% Mo resulted in the formation of coarse pearlite and thus impaired the toughness of the Fe-4Ni-0.5C steel. When 1.5wt% Cr was added into the Fe-4Ni-0.5C steel, bainite and Ni-rich martensite were formed. Thus, the toughness did not be deteriorated by the addition of Cr.
In terms of transverse rupture strength (TRS) and fatigue properties, we found that both Cr and Mo could improve the TRS and fatigue properties. In conclusion, this research successfully developed the powder metal steels with outstanding dynamic and static properties, including tensile strength, impact toughness, bending strength, and fatigue properties. As demonstrated in the Fe-4Ni-3Cr-0.5Mo-0.5C steel, the superior heterogeneous microstructure leads to the excellent tensile strength, 1323MPa, and transverse rupture strength, 2173MPa,respectively. The bending fatigue strength was higher than 700MPa.The impact energy was as high as 38.9J.

並列關鍵字

powder metal steels ； impact toughness ； fracture ； transverse rupture strength ； fatigue property

參考文獻

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