Eliminating brittleness

Research has markedly improved the toughness of high carbon hypereutectic high chromium white irons. *Dr Graham Powell writes

Research conducted at CSIRO and the University of Adelaide, supported by the Cooperative Research Centre for Welded Structures, has improved the strength of high-carbon, hypereutectic, high-chromium white irons.

The research is aimed at eliminating the high-carbon martensite surrounding M7C3 eutectic rods.

New alloys have been developed with fracture toughness equal to, or better than, the fracture toughness of heat treated low alloy steels frequently used in wear applications in the mining and mineral processing industries.

The fracture toughness of the new alloys has been tested by CSIRO and the wear resistance by the laboratories of the National Research Council of Canada at the University of British Columbia.

Foundries and heat-treatment facilities can manufacture the new alloys.

Historically heat-treated low alloy steels, in spite of their poor wear resistance, have been used in wear applications because of their superior toughness.

Standard fracture toughness tests and field trials have shown that the new high-chromium white irons, with high-fracture toughness and superior wear properties should, for many applications, replace heat treated low alloy steels.

Global Tough Alloys are commercialising the new alloys which are suitable for many applications over a wide temperature range (-196 °C to 1150 °C).

Room temperature applications include ground engaging tools, small to very large castings and welding consumables.

The compositions can be tailored to specific site conditions and for a wide range of environments.

Background

High-chromium white irons have long been used in many industries, including mineral processing, for their resistance to many forms of wear.

Since the mechanical properties of high-chromium white irons depends on their microstructure, it is not surprising that the introduction of various commercial electron microscopes starting in the late 1960s has resulted in a better understanding of the fine microstructure of high-chromium white irons.

Consequently, recent research has determined the cause of embrittlement and provided formulations for tough wear resistant high-chromium white irons in the as-solidified condition.

This has been the ‘Holy Grail’ of researchers for the last 40 years as toughness and wear resistance were seen as mutually exclusive in these alloys.

Ian Brown

Lecturer Materials and Manufacturing

Department of Mechanical Engineering

The University of Adelaide

08 8303 4703

0416 002 979

ian.brown@adelaide.edu.au

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