Erosion Resistance of Chromium–Manganese Iron Alloy Cast in Metal and Sand Moulds: PLS and DBAR Studies

Abstract

The wear-resistant high chromium (Cr: 16–19 %) iron alloyed with 5 % and 10 % manganese (Mn) was produced in metal and sand moulds by induction melting technique. The erosion resistance, hardness and microstructure were evaluated both in the as-cast and heat, treated conditions. The advanced nondestructive test (NDT) methods, namely Positron Lifetime Spectroscopy (PLS) and Doppler Broadening annihilation radiation (DBAR) studies, using variable energy positron beam were made use of to study the infl uence of metallurgical parameters on the defect sensitivity in the bulk and surface of the alloy. The data reveals that as the mould type is changed from metal to sand, the hardness decreases irrespective of the sample condition (i.e. as-cast or heat treated), whereas the erosion volume loss shows an increasing trend. The light and scanning electron microscopies give good support to these data fi ndings. It is observed that faster the cooling rate (metal mould), fi ner is the carbide size precipitation on the surface of the sample. The PLS data reveals that the defect size and its concentration are higher for sand mould alloy compared to metal mould. Reasons for lower erosion loss and fewer defects of smaller sizes in metal mould are attributed to faster heat transfer in the metal mould compared to the sand mould. Further, heat treatment of the samples yielded spherodization of carbides in the matrix and some of the defects seem to have been annealed out leaving only fewer defects of smaller size in the alloy. The S-parameter profi les of 10 % Mn both in AC and HT samples are almost identical indicating near absence of any modifi cation of defect structure near the surface following heat treatment in 10 % Mn sample, while 5 % Mn samples exhibit less defect concentration both at the surface as well as in bulk which agrees with the PLS results. Hence, the 5 % Mn bearing metal mould sample in the heat-treated condition is preferred choice as it shows higher hardness, lower erosion loss as well as least defect concentration with smaller defect sizes. Based on this investigation, a good correlation among erosion loss, DBA and PLS data has emerged.