Study on the Optimal Heat Treatment Conditions and Wear Resistance Property of High-Cr Cast Iron and Multi-component White Cast Iron
Date Issued
2008
Date
2008
Author(s)
Chang, Wei-Shin
Abstract
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.
Subjects
High-Cr cast iron
Multi-component white cast iron
Heat treatment
Wear resistance
Type
thesis
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