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Abstract AISI 440B martensitic stainless steels reinforced with up to 15 vol% NbC particles were successfully cast using a vacuum induction furnace. Energy dispersive x-ray spectroscopy, scanning electron microscopy and electron backscatter diffraction techniques revealed that NbC additions led to a slight decrease in the matrix solid solution Cr content, which was found to have a minor impact on uniform corrosion resistance. An ISO 21988 grade Cr27 martensitic eutectic white cast iron was used to benchmark the wear performance of the composites. Hardness, sliding wear tests, and erosion wear tests against a garnet slurry, showed that the composites could either match or surpass the cast iron despite having a lower total volume fraction of carbide phases. These results show that the proposed martensitic stainless steel composites have immense potential in high wear applications that require some degree of corrosion resistance, such as in the mining and mineral processing industry. Highlights • NbC - AISI 440 stainless steel composites were cast by vacuum induction melting. • NbC had a marginal effect on the corrosion resistance of AISI 440 stainless steels. • NbC was effective in improving hardness, and sliding and erosive wear resistance. • Compared to a Cr27 white cast iron alloy, the composites performed favorably. • The composites are potential alternatives to high-chromium white cast iron alloys. [ABSTRACT FROM AUTHOR]

AISI 440 stainless steels reinforced with various volume fractions of niobium carbide (NbC) particles of up to 25 vol% were fabricated in-situ using an argon arc furnace and then heat-treated to produce a martensitic matrix. Optical and scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and electron back-scatter diffraction (EBSD) techniques were used to analyze the microstructure, phases and composition of these composites. Interestingly, it was found that Chinese-script NbC could nucleate on existing primary NbC particles creating NbC clusters with complex microstructures. Additionally, hardness tests were used to evaluate viability in mining and mineral processing applications. The increase in NbC content resulted in an overall increase in the hardness of the composites while causing a marginal decrease in the amount of Cr in solid solution with the matrix, which could be a concern for corrosion resistance. The latter was due to the fact that the NbC lattice could dissolve a minor amount of Cr. Thermodynamic simulations also attributed this to a slight increase in M 7 C 3 precipitation. Nonetheless, these novel composites show great promise for applications in wear and corrosive environments. [ABSTRACT FROM AUTHOR]

It is often proposed that the wear performance of high-chromium white cast irons could be improved by adding Nb to form NbC. However, NbC can form with a needle-like "Chinese-script" morphology and/or as nodular particles, and clear evidence is not available as to which morphology is more beneficial against slurry erosion, a common application for these alloys. The lack of evidence is due to the difficulty of differentiating between the effect of NbC and that of a second type of carbide, M 7 C 3 , on slurry erosion resistance. Therefore, we created a martensitic stainless steel resembling the ferrous matrix of a typical high-chromium white cast iron, but without the M 7 C 3 phase, that was reinforced with Chinese-script NbC. A second specimen was prepared by substituting a small amount of Nb for Ti to inoculate the NbC, thus forming nodular particles. An AISI 440C stainless steel was used as a commercial benchmark since it has a similar hardness and microstructure. All three samples were subjected to slurry erosion tests against garnet and sand, with the Chinese-script NbC sample being the worst performer in both cases. Analysis of the worn surfaces revealed that the Chinese-script morphology promoted fracturing, resulting in a higher erosion rate. • NbC has been known to improve the wear performance in ferrous alloys. • NbC can form Chinese-script structures, dissolving Ti promotes a nodular structure. • NbC and (Nb,Ti)C-reinforced stainless steels were tested for slurry erosion. • Chinese-script NbC was particularly detrimental to slurry erosion. • This has implications for Nb-containing high-chromium white cast iron design. [ABSTRACT FROM AUTHOR]