Influence of Niobium Adding on the Microstructure and Abrasive Wear Resistance of a Heat-Treated High-Chromium Near-Eutectic Cast Iron Alloy

Abstract

High chromium cast iron (HCCI) with levels around 26% Cr - 2.9% C according to ASTM A 532 IIIA is widely used in systems where high abrasive wear resistance is required. To evaluate the niobium influence, HCCI with 0.5% Nb and 1% Nb additions were melted, besides one without niobium addition of for comparison. For characterization, X-ray diffractometry, scanning electron microscopy (SEM), Vickers microhardness tests, Rockwell C hardness, carbide quantifications, quantification of the retained austenite by Mössbauer spectroscopy, and rubber wheel abrasion test according to procedure A of ASTM G-65 were performed. The results indicated a reduction in the average size, average perimeter, and carbides volumetric fraction (CVF) due to the addition of niobium, also changing the microstructure of the HCCI from eutectic to hypoeutectic. In some regions, NbC_0.75 carbides formed a coating around M₇C₃ carbides. The 0.5% Nb alloy showed the best performance in the rubber wheel abrasive wear test, with a 37% average volume loss reduction as compared to the sample without niobium addition with a 130N load and 34% with a 45N load. The 0.5% Nb alloy also had the highest content of retained austenite among the investigated alloys.

Keywords:
Niobium; High Chromium Cast Iron; Abrasive Wear; Mössbauer Spectroscopy; Dry Sand Rubber Wheel