Development of an abrasion resistant steel composite with in situ TiC particles

摘要

Particles of crushed ferrotitanium (FeTi) were mixed with three iron-base powders of different carbon and alloy content as well as some graphite to obtain a metal matrix composite (MMC) by hot isostatic pressing (HIP) or hot uniaxial pressing (HUP) and an in situ transformation of the FeTi particles to TiC. In situ means "at the same site or position", i.e. a phase change within the particles by an inward diffusion of carbon. The HUP specimens were not fully dense but useful to study the microstructural transformation in time. Already after 4 mill at 1000°C, a hard TiC case had formed around the FeTi particles, the thickness of which increased up to 300 min. Iron and other impurities were enriched in the particle core, which did not transform to TiC. Pin-on-disc test with fully dense HIP specimens against flint, Al_2O_3 and SiC of 80 and 220 mesh size at room temperature revealed that the abrasive wear resistance of the new MMC with 10 vol.% in situ TiC particles, 63-100 μm in size and dispersed in a hardened steel matrix, was superior to a reference MMC with CrB_2 and close to one with WC/W_2C. A commercial MMC with 50 vol.% TiC particles of 1-4 μm in size showed a considerably lower wear resistance than the in situ MMC. Measuring the microhardness and specific scratch energy up to 600 and 700°C, respectively, indicate a potential of in situ TiC for elevated temperature service. The design of in situ MMC for wear protection is discussed, which is based on the larger size of in situ TiC particles compared to conventional ones and on the cost reduction.