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.

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Using the diagrams in Fig. Hawk, “Effect of carbide orientation on abrasion of high Cr white cast iron”, Wearpp. This behavior was encountered in other investigations [21] and could be explained by the slow solidification of the alloy. The influence of different cooling media after destabilization heat treatments on high chromium white cast iron was investigated. Improvement of abrasive wear resistance of the high chromium cast iron ASTM A through thermal treatment cycles.

A particular feature of the analyzed high chromium white cast iron was the presence of small amounts of M 23 C 6 carbides, which represent the Fe, Cr 23 C 6 type carbides [2], besides the M7C3 carbides. This hardness value is lower than the one obtained by Marathray et al.

Both the as-casting and the heat treated materials were structurally characterized in order to correlate the microstructural changes with the wear behavior. Different investigations were made on the effect of destabilization treatment parameters on the nature and morphology of secondary carbide precipitation as the distribution of secondary carbides in the martensitic ausenita after heat treatment is known to improve the wear resistance [9], due to their high hardness. These results are similar to those found by Hinckley et al.

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.

As the martensitic structure is recognized to provide a higher wear resistance, it was assumed that reducing the retained austenite to low percentages would lead to a better wear behavior. It should be noted that in the analyzed materials, the a phase is mainly associated to the ferrite phase.

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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 Zustenita 2 can effectively reduce the retained austenite, this is not enough to transform completely the retained ausgenita into martensite. Refenida, “Effect of destabilization heat treatments on the microstructure of high-chromium cast iron: It can also be observed that the secondary chromium carbides MC and MC nucleated and grew within the dendritic matrix.

After the heat treatments, the cast iron presented a transformation of the primary austenite to martensite, while the secondary chromium carbides M 7 C 3 and M 23 C 6 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.

While it was considered that the presence of residual austenite in the microstructure causes volumetric expansion which may also lead asutenita 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 [5].

The high demand of these materials led to the increment of imports in Colombia, while the local companies, that produce these materials, became a second option for the buyers. 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.

Estimation of the amount of retained austenite in austempered ductile irons

Additionally, in the center of the d endrite arms fine eutectic carbides were found, as their nucleation time from austenite was insufficient. According to the literature, the microstructure of the high-chromium white cast irons, influences the wear behavior.

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

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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 be more affected than in the case where the carbides are oriented parallel to the same area [29]. According to Bedolla-Jacuinde et al.

Austempered ductile cast irons

According to Liu 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. Also, the secondary carbides are distributed more homogeneously in the treated microstructures than in the as-cast one, this behavior xustenita also found by Wang et al.

The study is performed in order to determine the most suitable microstructure along with improved mechanical properties of HCWCIs produced in Colombia, through an appropriate heat treatment reenida could increase the wear resistance and hardness, and thus improving the production approach to international standards, and helping the local industries to strengthen their position in the international market.

Upon cooling, the austenite matrix becomes martensite because of the secondary carbide precipitation. A correlation between hardness and wear behavior volumetric loss and wear coefficient is given in Fig. Therefore, it was determined that the later cooling media can effectively reduce the proportion of austenite, which leads to the increment of fresh martensite content in the material, compared with the other cooling conditions, and it can also increase the fine secondary carbides precipitates, which can cause the dispersing strengthening effect.

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