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Despite being softer and more expensive than TiC, which is usually the preferred choice for reinforcements in a steel matrix, NbC has been shown to be a potential reinforcement for AISI 304 stainless steel matrix composites due to its favorable density with molten steels which ensures a more homogenous distribution of the second phase in the steel matrix and therefore more uniform properties throughout the casting. However, due to the solubility of NbC in the molten steel, the microstructure of the resulting steel composites present Chinese-script structures, which are not as effective in improving (and may even be detrimental to) wear performance as compared to discrete carbide particles. In this study, a unique solution is presented to the aforementioned problems; namely, by dissolving TiC in NbC, it is possible to obtain a stainless steel matrix composite reinforced with (Nb 0.75 ,Ti 0.25 )C which results in a higher particle hardness, a reduction in the occurrence of Chinese-script morphology, primary carbide refinement, better density matching, reduced costs, and significantly better wear resistance. [ABSTRACT FROM AUTHOR]

The study of sliding wear is important as it occurs in many industrial mechanical systems. In metal-ceramic sliding wear, reinforcing the metallic counterpart with ceramic particles transforms the system from a pure metal-ceramic interaction to one that contains both metal-ceramic and ceramic-ceramic interactions, which may improve the wear performance of both materials involved. This study shows that incorporating NbC particles into a bearing stainless steel reduces its wear rate against SiC, WC and Al 2 O 3 counterparts but its wear rate remained unchanged against ZrO 2. For the ceramic counterparts, SiC and WC also experienced reduced wear while Al 2 O 3 showed negligible wear across all tests. ZrO 2 , on the other hand, experienced a very high level of wear when the stainless steel contained 5 vol% NbC but the wear rate gradually decreased as the volume fraction of NbC increased to 15 vol%. Higher NbC volume fractions are thus expected to yield further improvement. • A bearing stainless steel was subjected to sliding against SiC, WC, Al 2 O 3 and ZrO 2. • Adding NbC into the steel reduced its wear loss against SiC, WC and Al 2 O 3. • Consequently, SiC and WC also experienced a reduction in wear losses. • Al 2 O 3 experienced negligible wear across all tests. • Adding low NbC amounts to the steel is very detrimental to the wear rate of ZrO 2. [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]