The relationship between abrasive wear resistance and microstructure of a hardfacing alloy based on the Fe-Cr-C-Nb-V system was investigated. This material was developed for cladding, by an open arc welding technique, of components subjected to severe abrasive wear. The work undertaken included the solidification study, microstructural characterization, and abrasion testing. Microstructural examinations of hardfaced layer showed that the microstructure of the alloy consisted of a large volume fraction of primary niobium carbides randomly dispersed in a metastable austenitic matrix containing fine M 3 C carbides and ''islands'' of eutectic mixture of c/M 7 C 3 . Energy dispersive X-ray analysis results showed that V preferentially partitioned into the NbC and M 3 C phases. In comparison with the conventional high carbon/high chromium hardfacing alloy with higher hardness, a Fe-Cr-C-Nb-V hardfacing alloy exhibited improved abrasive wear resistance and a microstructure with higher toughness.

The objective of this work is to investigate the correlation of microstructure with wear resistance in a hardfacing material reinforced with Fe-(TiW)C composite powder particles. This material was designed for cladding components subjected to highly abrasive conditions and was deposited on a low-carbon steel substrate by open arc welding. The theoretical and experimental work undertaken includes solidification study, microstructural characterization, and abrasive wear testing. Microstructural analysis of the hardfaced top layer of the alloy showed the presence of TiWC carbide particles and TiNbC carbides randomly distributed in a eutectic mixture matrix c/M 7 C 3 containing primary austenite dendrites. Microstructural examinations also showed that hard and fine spherulitic carbides, in which a Ti-rich MC carbide core was encircled by MC carbide enriched with Nb and W, were homogeneously distributed in the matrix. The energy-dispersive spectroscopy (EDS) mapping of spherulitic carbides showed that the any added Nb replaced a significant part of W in the Fe-(TiW)C powder, and W preferentially partitioned into other carbides and matrix during solidification. Abrasion test results showed that the preceding carbides improve the wear resistance of the hardfacing material in comparison with conventional Fe-Cr-C and Fe-Cr-C-Nb alloys, especially under high stress conditions.

A thermodynamic model was used to investigate the solidification of a hardfacing material in Fe-Cr-C-Nb system designated CNO, and developed for cladding components subjected to severe abrasive wear by welding. Microstructural characterization of the alloy showed that the theoretical simulations carried out to predict the amount and volume fraction of the phases using the module Scheil of MT-DATA Software gave very realistic results in the case of the rapid solidification of the hardfacing alloy CNO. The results obtained in this study indicate that the utilization of this tool may provide a good understanding of alloys solidification. As a consequence, it is possible to enable the refinement of alloy composition during the early stages of hardfacing materials development, leading to a decreasing of overall cost and time of manufacturing of hardfacing electrodes.

Neste trabalho, são empregadas simulações termodinâmicas para investigar a solidificação de uma liga Fe-Cr-C-Nb para solda de revestimento duro desenvolvida para revestir, por soldagem, componentes sujeitos a desgaste abrasivo severo. A caracterização microestrutural da liga mostrou que as simulações teóricas, utilizadas para prever as fases presentes e suas respectivas frações volumétricas, usando o módulo Scheil do programa MT-DATA, obteve resultados com excelente concordância no caso da solidificação da liga em altas taxas de resfriamento (20 K.s-1-30 K.s-1). Os resultados obtidos neste estudo indicam que a utilização destas simulações pode proporcionar um bom entendimento do comportamento das ligas durante a solidificação e, conseqüentemente, permitir a otimização da composição das mesmas durante os estágios iniciais de desenvolvimento, de tal forma a maximizar a resistência ao desgaste com a menor quantidade de elementos de adição. Com isto, torna-se possível uma diminuição do tempo e do custo de fabricação dos eletrodos para solda de revestimento duro. Palavras-chave: Desenvolvimento; Liga para solda de revestimento; Simulações termodinâmicas.