AUSTENITA RETENIDA PDF

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.

Therefore, the carbides can be more easily removed and cracked during wear. A totalof ten indentations were made on each sample andaveraged to determine the hardness of each sample.

A high chromium white cast iron manufactured by a regional company was used in this investigation. V is the volume of the lost material mm 3 ,H represents the material hardness BrinellP is the load used in the tests kg and L is the sliding distance mm.

While the as-cast presented a lower hardness and consequently a lower wear resistance, after the heat treatments the samples showed an improvement of these characteristics, due to the precipitation of secondary carbides within the martensite matrix and reduction of retained austenite.

Austempered ductile cast irons

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 ausetnita might lead to a decrease in the abrasion resistance.

This hardness value is lower than the one obtained by Marathray et al.

The material composition is summarized in Table I. This increased hardness could be the result of the precipitation of secondary carbides, which destabilized the austenite leading to the formation of a martensite matrix, by increasing the matrix strength through a dispersion hardening effect; the fine secondary carbides can increase the mechanical support of the eutectic carbides [24].

By means of XRD analysis, the retained austenite percentage was determined in the heat treated samples. It can be observed that the samples subjected to destabilization and cooled in air present a more homogeneous distribution of finer carbides in the structure, compared with the other samples.

Estimation of the amount of retained austenite in austempered ductile irons

The microstuctural behavior of the as-received cast iron is given in Figure 4a. An additional influence on the wear behavior is given by the secondary carbides [7], which improves the mechanical strength [8], through increasing the matrix strength.

It should be noted that in the analyzed materials, the a phase is mainly associated to the ferrite phase. It can also be observed that the secondary chromium carbides MC and MC nucleated and grew within the dendritic matrix.

However, it was determined that even though a low percentage of retained austenite 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.

Hawk, “Effect of carbide orientation on abrasion of high Cr white cast iron”, Wearpp. Sare, “Abrasion resistance and fracture toughness of white cast irons”, Met.

The low retained austenite percentages improve bulk hardness, but they decrease the abrasion resistance of the high chromium cast iron. 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 [27].

During the heat treatment, the ferrous matrix is supersaturated with carbon and chromium leading to the precipitation of secondary carbides. Although the cementite is practically removed due to the high proportion of chromium found in the used HCWCI, some traces of cementite may be present.

It was observed that the destabilization treatment reduced the retained austenite content by a factor of from the percentage found in the as-cast samples.

According to the literature, the microstructure of the high-chromium white cast irons, influences the wear behavior. The resulting carbide percentage was around According to Liu et al. Therefore, it was determined that the austenitz cooling media can effectively reduce the proportion of austenira, which leads to the increment of fresh martensite content in the material, compared with the other cooling conditions, and it can austeniga increase the fine secondary carbides precipitates, which can cause the dispersing strengthening effect.

Thus, 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 [5]. Gates, “A transformation toughening white cast iron”, Journal of Materials Science 32, pp.

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, the diffraction when quenching in oil is run to the left and presents interferences.

Following the investigation of Bedolla-Jacuinde et al. A correlation between hardness and wear behavior volumetric loss and wear coefficient is given in Fig. It was determined that the matrix structure is predominantly austenite austenite dendrites proeutecticwith an approximate 1.