碳、鎢含量及熱處理條件對多元合金白口鑄鐵顯微組織與耐磨耗性質之影響

本研究針對應用於熱滾軋輥輪的多元合金白口鑄鐵(Multi-component white cast iron)，選用Fe-2% C-5% Cr-5% Mo-6% V-2% Co-2%W為基本合金組成，探討不同W、C含量及熱處理參數（austenitization溫度、回火溫度）對合金之顯微組織與耐磨耗性之影響。研究結果顯示，合金A（含2% C-2.1%W）及合金B（含2% C-0.21%W）之鑄態顯微組織包含共晶碳化物MC、M2C及沃斯田鐵基地組織，合金C（含2.5% C-2.1% W）之鑄態顯微組織則包含初晶MC碳化物、共晶碳化物MC、M7C3、M2C及沃斯田鐵基地組織。上述三種合金經淬火及回火後，碳化物之形態、分佈及含量幾無變化，基地組織則由沃斯田鐵變態為回火麻田散鐵，而殘留沃斯田鐵量隨回火溫度之升高而逐漸降低，在525~545℃時，殘留沃斯田鐵量幾已降至零。又，硬度值隨回火溫度之升高首先增加，在525~545℃達到最高值，然後再隨回火溫度之增高而降低。磨耗率隨回火溫度之變化與硬度隨回火溫度之變化呈相反之趨勢，亦即最低磨耗率發生在硬度最高處，此亦對應於殘留沃斯田鐵量幾降至零之處。本研究所獲致之多合金白口鑄鐵最佳熱處理條件為：1100℃-70 min (austenitization)+強風冷卻(quench)+(525~545℃)-3hr(tempering)，施以此熱處理條件後之多元合金白口鑄鐵具有最高之硬度及最佳之耐磨耗性。又，降低W含量（由2.1%降至0.21%）及增加C含量（由2.0%增至2.5%）均有助於提升合金之硬度及耐磨耗性，其中又以增加C含量之效果較為顯著。

關鍵字

多元合金白口鑄鐵；熱處理；殘留沃斯田鐵；耐磨耗性

並列摘要

In this study, minor modifications of C and W contents from the base alloy composition of Fe-2%C-5%Cr-5%Mo-6%V-2%Co-2%W were performed to evaluate their effects on the response of heat treatment and wear resistance. The results show that the as-cast microstructure of the base alloy (Alloy A) contains both MC-type and M2C-type carbides in an austenitic matrix. Reducing the W content from 2.0% to almost nil (Alloy B), the features of main microstructure are essentially the same as Alloy A, except that the volume fraction of (γ+M2C) eutectic is less. On the other hand, when the C content was raised to around 2.5% (Alloy C), in addition to eutectics MC and M2C, primary MC and traces of eutectic M7C3 can also be observed. The macro-hardness of all three alloys increases first with increasing tempering temperature, reaches a maximum value, and then decreases with a further increase in tempering temperature. The peak tempered hardness (H(subscript Tmax)) was obtained when tempered within 525~545℃ (798K~818K) with minor variations in different alloys. As for the volume fraction of retained austenite (V(subscript γ)), it decreases continuously with increasing tempering temperature, and reaches almost nil at a point corresponding roughly to the H(subscript Tmax). In addition, increasing austenitizing temperature tends to obtain higher H(subscript Tmax). Regarding the wear resistance property, the pattern of the change in wear rate with tempering temperature exhibits just opposite to the behavior of macro-hardness for all three alloys, with the minimum Rw coinciding well with the H(subscript Tmax). The optimal heat treatment condition has been found to be: 1100℃-70min/Forced airquench/(525~545℃) -3hr. In addition, an improved wear resistance or a decrease in Rw was achieved by increasing austenitizing temperature. Furthermore, the wear rate decreases as the W content is reduced from 2.0% to nil, and further decreases as the C content is increased from 2.0% to 2.5%.

並列關鍵字

multi-component white cast iron ； heat treatment ； retained austenite ； wear resistance

國際替代計量

碳、鎢含量及熱處理條件對多元合金白口鑄鐵顯微組織與耐磨耗性質之影響

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