高鉻鑄鐵及多元合金白口鑄鐵之最佳熱處理條件及耐磨耗性質探討

Study on the Optimal Heat Treatment Conditions and Wear Resistance Property of High-Cr Cast Iron and Multi-component White Cast Iron

張維鑫(Wei-Shin Chang)

指導教授 ： 潘永寧

國立臺灣大學/工學院/機械工程學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.01452

摘要

本研究針對雙相輥輪(高鉻白口鑄鐵/球墨鑄鐵)之外層高鉻鑄鐵(High-Cr cast iron)，探討熱處理參數(回火溫度)對於高鉻鑄鐵之顯微組織及耐磨耗性之影響，以期獲致高硬度及優良耐磨耗性之最佳熱處理條件，並提供輥輪之熱處理參考。研究結果顯示，經熱處理後之顯微組織主要包含回火麻田散鐵(內含M7C3二次碳化物)、共晶碳化物M7C3及少量之殘留沃斯田鐵，其中，殘留沃斯田鐵量隨回火溫度之升高而減少，當回火溫度高於500oC時，殘留沃斯田鐵量降至3%以下。又，硬度隨回火溫度之升高首先增加，在約500oC達到最高值，然後再隨回火溫度之升高而降低。另外，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。本研究所獲致之高鉻鑄鐵最佳熱處理條件為：(1000~1050)oC-2hr(destabilization) +強風冷卻(quench)+ 500oC-6hr (tempering)。
此外，本研究亦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，而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525~545oC時，殘留沃斯田鐵幾已降至零。又，硬度隨回火溫度之升高首先增加，在525~545oC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：1100oC-70min(austenitization) +強風冷卻(quench) + (525~545oC)-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

高鉻鑄鐵 ； 多元合金鑄鐵 ； 熱處理 ； 顯微組織 ； 硬度 ； 耐磨耗性

並列摘要

The objective of this study is to obtain the optimal heat treatment conditions (tempering treatment in specific) for achieving the required wear resistant property for both high-Cr (~15%Cr) cast iron used in the outer shell of bi-metal rolls and multi-component white cast iron used in hot milling rolls. The experimental results indicate that the quenched and tempered microstructures consist of temper martensite (contains numerous fine global secondary M7C3 carbides), eutectic M7C3 carbides, and retained austenite. The amount of retained austenite decreases with increasing tempering temperature, and the amount is reduced to below 3% as the tempering temperature exceeds 500oC. In addition, the hardness value increases first with increasing tempering temperature, reaches peak hardness at around 500oC, and then decreases with further increase in tempering temperature. Furthermore, the change in wear resistance of the treated alloys as affected by tempering temperature shows a reverse trend as that of hardness. Finally, the optimal heat treatment condition has been obtained to be: Destabilization: (1000~1050)oC-2hr/ Quench: forced air cooling/ Tempering: 500oC-6hr.
For multi-component white cast irons, 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 made to evaluate their effects on the response of heat treatment and wear resistance property. The results show that the peak tempered hardness (HTmax) was achieved when tempered within 525~545oC with minor variations in different alloys. In addition, the occurrence of the minimum wear rate (Rw) coincides with the HTmax and nil retained austenite (Vγ) in the tempered state. Furthermore, an improved wear resistance was obtained by increasing austenitizing temperature, or by reducing the W content, or by increasing the C content. Finally, the optimal heat treatment condition has been obtained to be: Austenitization: 1100oC-70min/ Quench: forced air cooling/ Tempering: 525~545oC-3hr.

並列關鍵字

High-Cr cast iron ； Multi-component white cast iron ； Heat treatment ； Wear resistance

參考文獻

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