Mejoramiento de la resistencia al desgaste abrasivo de la fundición al alto cromo ASTM A-532 a través de ciclos de tratamiento térmico

Abstract

High-Chromium White Cast Iron is a material highly used in mining and drilling shafts for oil extraction, due to its high wear resistance. However, because of the austenitic matrix found in the as-cast state, an adequate heat treatment cycle is necessary. This paper studies the effects of different cooling media after a destabilization treatment on the microstructure, hardening and abrasion resistance behaviors of a hypoeutectic high chromium white cast iron. The results show that although air cooling followed by immersion in CO 2 can effectively reduce the retained austenite, this is not enough to transform completely the retained austenite into martensite. The low retained austenite percentages improve bulk hardness, but they decrease the abrasion resistance of the high chromium cast iron. The best combination of hardness and wear resistance was found in the samples cooled in air, due to the percentage of retained austenite and a moderate precipitation of chromium carbide.Keywords: High chromium white cast iron, HCWCI, White cast iron, Chromium carbides, Hardness, Wear testing, Austenite, Martensite. Improvement of abrasive wear resistance of the high chromium cast iron ASTM A-532 through thermal treatment cycles ResumenLas fundiciones blancas de hierro al alto cromo son muy usadas en la minería y en la perforación de pozos petroleros, debido a su alta resistencia al desgaste; sin embargo, debido a que en el estado de colada su microestructura es austenítica, es necesario someterlas a un adecuado ciclo de tratamiento térmico. Este trabajo estudia los efectos de los diferentes medios de enfriamiento después de un tratamiento de desestabilización de la microestructura y, por ende, el efecto del grado de endurecimiento sobre el comportamiento a la abrasión de una fundición blanca al alto cromo hipoeutéctica. Los resultados muestran que a pesar de que el enfriamiento al aire, seguido por inmersión en CO 2 , puede reducir eficazmente la austenita retenida, esto no es suficiente para transformarla completamente en martensita. El bajo porcentaje de austenita retenida incrementa la dureza del material, pero disminuye la resistencia a la abrasión de las fundiciones al alto cromo. La mejor combinación de dureza y resistencia al desgaste se encontró en las muestras enfriadas al aire, debido al porcentaje de austenita retenida y a una moderada precipitación de carburos de cromo.Palabras clave: HCWCI, Fundiciones blancas de hierro, Fundición al alto cromo, Carburos de cromo, Austenita, Martensita. ResumoAs fundições brancas de ferro ao alto cromo são muito usadas na mineração e na perfuração de poços petroleiros, devido a sua alta resistência ao desgaste; porém, devido a que no estado de lingotamento sua microestrutura é austenítica, é necessário submetê-las a um adequado ciclo de tratamento térmico. Este trabalho estuda os efeitos dos diferentes meios de resfriamento depois de um tratamento de desestabilização da microestrutura e, consequentemente, o efeito do grau de endurecimento sobre o comportamento à abrasão ...

Destabilization Heat Treatment Effect on Erosive Wear Characteristics of High Chromium White Cast Iron

“…It was confirmed that austenite phase expected in the structure had transformed into martensite after the heat treatment. A small amount of retained austenite was observed, consistent with the reported results (Higuera-Cobos et al, 2016;Zhi et al, 2008;Gasan and Erturk, 2013). Fig.…”

“…While it was considered that the presence of residual austenite in the microstructure causes volumetric expansion which may also lead to microcracks because of the developed stresses, some investigations determined that a certain percentage of retained austenite could improve the abrasion resistance, due to its work-hardening properties, ductility and thermodynamic metastability at room temperature (Doğan et al, 1997;Liu et al, 2008). Therefore, the microstructure must present a tough matrix and high volume fraction of hard chromium carbides, such as a high carbon hard martensite matrix hardened by secondary carbides, because retained austenite reduces the hardness which might lead to a decrease in the abrasion resistance" (Çetinkaya, 2006;Tang, 2011;Higuera-Cobos et al, 2016).…”

Influence of Niobium Addition on Microstructure and Machinability of High Chromium Cast Iron

“…M 7 C 3 chromium carbides were identified in all heat treatment phases and in all the analysed samples. The peaks for M 7 C 3 can be identified at 39, 43, 44.5, 51 and 82.5°, and these peaks were found in a similar way by other authors, such as Higuera-Cobos et al 25 and Ibrahim et al 20 . The peaks visible at 44.5 and 82.5° indicate a peak coincidence between chromium carbide and ferrite/martensite, as well as the peak at 51° indicates an overlap of austenite and chromium carbide peaks.…”

“…The peaks visible at 44.5 and 82.5° indicate a peak coincidence between chromium carbide and ferrite/martensite, as well as the peak at 51° indicates an overlap of austenite and chromium carbide peaks. This overlap was similarly identified by Higuera-Cobos et al 25 .…”

Efecto del tratamiento sub-cero sobre la microestructura y dureza de fundiciones blancas alto cromo

“…El contenido de austenita retenida presente en piezas en estado de colada y tratadas térmicamente es una de las principales causas de agrietamiento superficial producto de la trasformación a martensita que ésta sufre en servicio [4,9,10,11]. Por este motivo y con el fin de reducir los niveles de austenita retenida presente, estas aleaciones pueden ser sometidas a diversos tratamientos térmicos [12,13].…”