Study on Castable Duplex Stainless Steel 2205 Based Metal Matrix Composites
T. Tang, K. Dolman
Materials R&D, Weir Minerals, Artarmon,2064, Australia
White Cast Irons (WCIs) are widely used in Weir Minerals’ slurry handling equipment for mining and mineral processing industries that require materials with good corrosion and wear resistance. The wear resistance of WCIs results from hard chromium carbides (mainly M7C3 with hardness of ~1500 HV), and the corrosion resistance is dominated by free chromium in ferrous matrix. However, due to very harsh mining environment and severe working conditions, regular WCIs do not always perform satisfactorily.
Technically speaking, Metal Matrix Composites (MMCs) consisting of extremely hard refractory carbides (dispersed phase) and stainless steels (matrix) can provide superior wear and corrosion resistance for slurry equipment, i.e., Flue Gas Desulfurization (FGD) pumps. MMCs can be fabricated by various technologies, i.e., powder metallurgy, laser bonding, physical vapor deposition, etc., but casting may be the most economic manufacturing practice, especially for components with complex shape. However, challenges have to be overcome in casting MMCs including: 1) segregation due to density difference between refractory carbide and host metal; 2) solubility of refractory particles in the host metals; 3) refractory particle-host metal matrix bonding; and 4) casting defects.
By replacing ferrous matrix and chromium carbide of WCIs by Duplex Stainless Steel 2205 (DSS) and MC carbides, respectively, DSS-MC composites have been made successfully. The density of MC carbides was precisely tailored, solving the segregation concern in casting, without changing the microstructure and the chemistry of the host metal, DSS. In another words, the outstanding properties of DSS were remained in the as-prepared DSS-MC composites (see Fig.1). Moreover, the in situ synthesized MC carbides can effectively eliminate the interface incompatibility between the matrix and the reinforcing particles, since nucleating and growing thermodynamically stable MC carbides result in good bonding with the surrounded matrix. It was found that MC carbides are not only significantly harder, but also tougher than eutectic M7C3. DSS-MC composites enhance key engineering properties of castings, particularly suitable for wear and corrosion products for heavy duty application. The future work will focus on controlling the shape of MC carbides, reducing cost in manufacture, etc.
Fig.1 SEM images of DSS-MC MMCs