This work assesses the wear resistance behavior of different high Cr and Nb alloyed hardfacing deposits carried out by Self-shielded Flux Cored Arc Welding, considering the resulting microstructures as base for the analysis. To obtain non-commercial alloys, an "in-situ" technique was employed with addition of cold wire into the weld pool. Six combinations of two commercial FeCrC and FeCrNbC tubular wires and three different solid wires (AWS ER 70S-6, ER308LSi and ER 430) were used to obtain white cast iron hardfacing deposits on plain carbon steel subtracts. The welding parameters were identical for all combinations. Each deposit was characterized taking into account the resulting microstructure, hardness and abrasion wear resistance. The addition of a ferritic stainless solid wire in the weld pool resulted in the best wear resistance, which was boosted if Nb is present in the S-FCAW wire. The reason for these results was microstructure refinement and the presence of NbC and M 7 C 3 , the latter being present in all combinations.
Resumen: Se aborda el efecto de los contenidos de matriz, grafito y ferrocromo-manganeso en fundentes SAW, obtenidos con escorias de acería y cenizas de cascarilla del arroz, sobre la composición y dureza del metal depositado en una camada. Fueron establecidos vínculos entre las variables de composición del fundente (X1 – Matriz (72,99% de escoria, 20,44% de cenizas de cascarilla del arroz y 6,57% de fluorita), X2- Grafito y X3- Ferrocromo-manganeso) y los contenidos de carbono, cromo, manganeso, silicio, la microdureza y la dureza del depósito y fueron adquiridas imágenes metalográficas. El depósito del fundente de mejor desempeño fue evaluado mediante ensayo de desgaste microabrasivo, frente a un depósito comercial de referencia. Se concluye, que el contenido de carbono, la microdureza y la dureza del metal depositado son gobernado por el grafito y que los contenidos de cromo, manganeso y silicio son gobernados por el ferrocromo-manganeso; que el fundente de mejor desempeño corresponde a, 88% de matriz, 7% de grafito y 5% de ferrocromo-manganeso, con dureza del depósito de 59 HRc, y con microestructura de martensita y austenita interdendrítica. Este se comporta al desgaste adecuadamente, siendo un 6% menos resistente que el de referencia.
The objective of this work was to study the effect of the heat treatment and further operation aging on the stereological parameters (size, quantity and volume fraction) of precipitates within ferrite grains of a creep-resistant 1.25Cr0.5Mo steel after long-term operation. The heat treatment was similar to the treatment that is carried out in industrial steam pipelines after welding (post weld heat treatment - PWHT) during installation and/or repairing. The operation aging corresponds to a subsequent long in-service operation after repairing. To determine the stereological parameters, SEM digital images were taken from samples of this material after conditions of in-service-aged (after long-term operation), in-service-aged and heat-treated (simulating repairing) and in-service-aged, heat-treated and in-laboratory aged (simulating subsequent long-term operation after repairing). The results indicate that the changes in the stereological parameters of the precipitates within ferrite grains after PWHT is associated with the coarsening process of the within-ferrite-grain precipitates as well as stabilizing the microstructure, since the material aging after PWHT of an in-serviced aged material would not change the stereological parameters.
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