Processes-Induced Structural Transformations and the Impact Properties of Cr–Mn Iron Systems

Abstract

High chromium irons are well known for their good wear resistance. Since they are brittle, they tend to fracture under impact. Hence, there is a need to improve the impact property with minimal reduction in wear characteristics. Towards this end, manganese, known for its tendency to retain austenite and containing 5 and 10% in chromium (∼16–19%) irons has been tried.

Since the mechanical properties are microstructure sensitive, the castings are made in both metal and sand moulds followed by thermal treatment. The as-cast and heat-treated samples are examined microstructurally and then evaluated for hardness, and impact properties.

While the hardness decreases with increase in manganese content from 5 to 10% irrespective of the sample condition (i.e., mould type/heat treatment adopted), the impact property shows two different trends. The 10% metal cooled manganese bearing sample exhibits higher values compared to the 5% ones. On the other hand, for the sand case, 5% manganese shows higher impact energy compared to the 10% ones. Thus, there is a reversal in the impact behavior for the same level of increase in manganese content for these two cases. These findings are correlated with the structural features noticed through microscopy.

Keywords:

• As-cast
• Chromium–manganese irons
• Heat-treated
• Impact energy
• Metal and sand moulds
• Optical and scanning electron microscopy

ACKNOWLEDGMENTS

The authors thank the management of Central Power Research Institute for having accorded permission to publish this article. The authors wish to thank Mr. B. S. Manjunath of MTD, CPRI for the assistance rendered in preparing the text. One of the authors (Kishore) would like to thank CSIR for the award of fellowship under Em. Sc. Scheme.