Microstructure and Hardness of Single- and Two-Layer Hardfaced Coatings for Blast Furnace Charging Components

Blast furnace charging components are subjected to severe abrasive and impact loading during burden distribution. Hardfacing is the principal technology for extending their service life, yet comparative studies of commercially available Fe-Cr-C consumables under industrially representative conditions remain limited. Four commercial Fe-Cr-C consumables (powder PG-S27; flux-cored wires PP-AN170, Castolin OA-4625, and Sabaros 305) were deposited in single- and two-layer configurations and characterized by optical metallography, Rockwell hardness, and microhardness measurements. Since no direct wear tests were performed, a calculated wear-resistance index was derived from the matrix microhardness using the empirical Khrushchev relationship. It is a comparative, hardness-based descriptor rather than a measured wear property. Alloy composition and layer configuration jointly determined the microstructure and hardness of the deposits. Castolin OA-4625 and Sabaros 305 formed hypereutectic structures with the highest volume fractions of primary carbides tentatively identified as M7C3 (25.9% and 27.0%), bulk hardness of 59–62 HRC, and calculated ε of 2.33 and 2.43 (two-layer deposits). Their single-layer deposits exhibited lower hardness (54–56 HRC) owing to dilution by the base metal, confirming that at least two deposited layers are required to develop the designed wear-resistant structure. Sabaros 305 exhibited stress-relief cracking typical of high-carbon Fe-Cr-C hardfacings; within the limited observation period (2006–2007, three recorded replacement events) the cracks were not associated with premature replacement. Qualitative comparison with long-term service records (1971–2007) is broadly consistent with the laboratory-based ordering of materials I, III, and IV; material II has no industrial counterpart. The available plant records suggest that elevated top-gas temperature and dust carry-over are associated with reduced service life, although the present data do not allow these factors to be formally ranked.