Los resultados muestran que a pesar de que el enfriamiento al aire, seguido por inmersión en CO2, puede reducir eficazmente la austenita retenida, esto no es. microestructura del material está formada por dendritas finas de austenita men de austenita retenida depende de manera crítica de los parámetros del. microestructuras son extraordinariamente duras ( HV) y resistentes (2,5 GPa) . Palabras clave. Bainita. Austenita retenida. Aceros. Transformaciones de fase.
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Hardness tests of the analyzed samples were performed on a Brinell hardness tester. The Austeniga Chromium White Cast Iron HCWCI is a material highly used in the mining and oil industry, to manufacture crushing hammers and drilling rigs, due to the presence of a significant proportion quantity of chromium rich carbide phase in their microstructures.
Estimation of the amount of retained austenite in austempered ductile irons
Following the investigation of Bedolla-Jacuinde et al. Sare, “Abrasion resistance and fracture toughness of white cast irons”, Met. It should be noted that in the analyzed materials, the a phase is mainly associated to the ferrite phase.
Due to the precipitation of secondary carbides within the martensite matrix, after the destabilization heat treatment, the samples present an increase in the hardness which leads to a wear resistance higher than that of the as-received material.
According to Liu et al. However, the diffraction when quenching in oil is run to the left and presents interferences.
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 [3, 4], ductility and thermodynamic metastability at room temperature .
The samples cooled in air showed the best results regarding the abrasion resistance hardness because of the optimal combination between retained austenite and moderate precipitation of chromium carbide. The resulting carbide percentage was around The high demand of these materials led to the increment of austrnita in Colombia, while the local companies, that produce these materials, became a second option for the buyers.
Therefore, the as-cast microstructure is made of dendrites, which remain fully austenitic at room temperature, while the eutectic micro-constituent is a continuous network of chromium-rich carbides and eutectic austenite, similar to the investigation realized by Hann et al. Also, the direction in which the carbides are oriented influences the abrasive wear resistance, since, if the carbides are perpendicular to the surface being subjected to friction, it will austenuta more affected than in the case ausstenita the carbides are oriented parallel to the same area .
Improvement of abrasive wear resistance of the high chromium cast iron ASTM A through thermal treatment cycles. Austenitaa chemical composition of the studied high chromium white cast iron was marked with 1 in Fig. Reteida, when the undercooling is smaller because of the heat released by the formation of the M 7 C 3 carbidesthis type of carbide shape is favored .
A correlation austenitw hardness and wear behavior volumetric loss and wear coefficient is given in Fig. Different investigations were made on the effect of destabilization treatment parameters on the nature retenlda morphology of secondary carbide precipitation as the distribution of secondary carbides in the martensitic matrix after heat treatment is known to improve the wear resistance , due to their high hardness. This behavior was encountered in other investigations  and could be explained by the slow solidification of the alloy.
The material composition is summarized in Table I. However, it was determined that even though a low percentage of retained auxtenita could improve the hardness values, it could negatively affect the wear resistance, as it can be seen for the samples subjected to destabilization followed by cooling in air and subsequently overcooled in CO 2. This paper studies the ertenida of different cooling media after a destabilization treatment on the microstructure, hardening and abrasion resistance behaviors of a hypoeutectic high chromium white cast iron.
Similar to the as-received sample, it can be seen in Fig. After the hardness values were obtained, the wear coefficient Ks was calculated according to equation 2 :. Given detenida above problem, the aim of the present investigation is to establish the effect of different cooling media used after destabilization treatment on the wear resistance of a white cast iron.
Austempered ductile cast irons
It can also be observed that the secondary chromium carbides MC and MC nucleated and grew within the dendritic matrix. Gates, “A transformation toughening white cast iron”, Journal of Materials Science 32, pp.
Thus, the high degree of strain hardening that occurs in the austenitic matrix, as a result of the plastic deformation caused by the normal and the tangential forces of the moving abrasive particles, leads to a lower wear resistance in the as-cast material .
The microstuctural behavior of the as-received cast iron is given in Figure 4a. It can be seen that the as-received cast iron presents a lower hardness and higher values of volumetric loss and wear coefficient than the heat treated samples, showing the dependence of the wear behavior on the matrix microstructure. According to Bedolla-Jacuinde et al. Therefore, the microstructure must present a tough matrix and high volume fraction of hard chromium carbides [9, 10], 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.
The influence of different cooling media after destabilization heat treatments on high retejida white cast iron was investigated. This increase in imports is caused by the better performance of the tools, as the duration of the materials is about 4-four times higher, than the tools manufactured locally. This transformation process is critical for the wear behavior of high chromium cast irons because it is believed that the austenite generates the spalling process, the main cause of damage to this material under working conditions .
High-Chromium White Cast Iron is a material highly used in mining and drilling shafts for oil extraction, due to its high wear resistance.
It was determined that the matrix structure is predominantly austenite austenite dendrites proeutecticwith an approximate 1. According to the literature, the microstructure of the high-chromium white cast irons, influences the wear behavior.
Gates, “The role of secondary carbide precipitation on the fracture toughness of a reduced carbon white iron”, Mater.