Microstructure and Tempering Behaviour of 28Cr-2.5C-1W Cast Irons

Abstract:

In this work, the effects of 1 wt.% tungsten addition and variation in tempering times on the microstructure and hardness of nominal 28 wt.%Cr high chromium irons were investigated. As-cast samples were destabilised at 1050 °C for 4 hours and then hardened by air cooling. Tempering after destabilisation was carried out at 450 °C for 2, 4 and 6 hours followed by air cooling. X-ray diffractometry, light microscopy and scanning electron microscopy were used to characterize the microstructures of the irons. The results show that the as-cast microstructure of the iron without W addition consisted of primary austenite dendrites with eutectic M₇C₃ and eutectic austenite partially transformed to martensite. The iron with 1 wt.%W addition contained primary M₇C₃ and eutectic M₇C₃ in an austenite matrix. Destabilisation treatment of the austenite matrix in both irons allowed precipitation of secondary carbides and transformation to martensite during air cooling. Phase transformation of eutectic M₇C₃ was also found in the iron with W addition. The formation of primary M₇C₃ in the 1 wt.%W iron increased the as-cast macro-hardness from 500 (no W) to 576 HV₃₀. Destabilisation increased the macro-hardness up to 736 (no W) and 780 HV₃₀ (1 wt.%W) since secondary carbide precipitation allowed austenite to transform to essentially martensitic matrices. At longer tempering times, the macro-hardness further increased up to about 820 HV₃₀.

• Periodical: Solid State Phenomena (Volume 283)
• Pages: 116-123
• DOI: https://doi.org/10.4028/www.scientific.net/SSP.283.116
• Online since: September 2018
• Authors: Sasitorn Yeekew, Amporn Wiengmoon*, Torranin Chairuangsri, John T.H. Pearce
• Keywords: Heat Treatment, High Chromium Iron, Microstructure, Tungsten

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