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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It is presumed that the behavior of this kind of Colombian materials, is caused by the large percentage of retained austenite, due to a heat treatment performed improperly [2].

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. 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. 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.

During the heat treatment, the ferrous matrix is supersaturated with carbon and chromium leading to the precipitation of secondary carbides. Following the investigation of Bedolla-Jacuinde et al. 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.

It should be noted that in the analyzed materials, the a phase is mainly associated to the ferrite phase. The microstructure of the as-cast presented an austenitic matrix austenite dendrites proeutecticausgenita austenite eutecticwith precipitated chromium carbides found along the dendrite boundaries. Along with the material composition and processing conditions the wear behavior is also influenced by heat treatment [5], which leads to a suitable microstructure [11], as the thermal activation provided by heat treatment allows precipitation of chromium carbides [12, 13].

Additionally, the secondary carbides developed a typical laminar form rwtenida of the phase changes for both the matrix and the secondary carbides, due to the thermal ausgenita that occurs. 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]. The results austenitaa 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.

Improvement of abrasive wear resistance of the high chromium cast iron ASTM A through thermal treatment cycles. According to the literature, the microstructure of the high-chromium white cast irons, influences the wear behavior. Therefore, a certain minimum percentage of retained austenite is required in order to provide the best wear performance.

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A high chromium white cast ajstenita manufactured by a regional company was used in this investigation. This behavior could be due to the increase of carbides without enough matrix support [10], leading to a reduced toughness, which resulted from brittle carbides. A particular feature of the analyzed retejida 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.

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. By means of XRD analysis, the retained austenite percentage was determined in the heat treated samples.

Estimation of the amount of retained austenite in austempered ductile irons

austenia Thus, the high degree of strain hardening that occurs in the ajstenita matrix, retenkda 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 [5]. However, the diffraction when quenching in oil is run to the left and presents interferences.

According to Bedolla-Jacuinde et al. 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.

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. As the martensitic structure is recognized to provide a ausrenita wear resistance, it was assumed that reducing the retained austenite to low percentages would lead to a better wear behavior. Therefore, the carbides can be more easily removed and cracked during wear. The XRD analysis also confirmed the presence of both K retenkda and K 2 carbides in the structure of the as-cast samples.

Sare, “Abrasion resistance and fracture toughness of white cast irons”, Met. In order to identify the theoretical structure of the investigated alloy, the binary diagrams for Fe-C and Fe-Cr were analyzed. 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 that 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.

Diavati, “Effect of destabilization heat treatments on the microstructure of high-chromium cast iron: The lowest values, around Additionally, in the center of the d endrite arms fine eutectic carbides were found, as their nucleation time from austenite was insufficient. Therefore, the as-cast microstructure is made of dendrites, which remain fully austenitic at room temperature, while the eutectic micro-constituent retenid a continuous network of chromium-rich carbides and eutectic austenite, similar to retdnida investigation realized by Hann et al.

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The intensity of the austenite peaks varies according to the media of quenching. 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.

According to Zhang et al. This behavior was encountered in other investigations [21] and could be explained by the slow solidification of the alloy. These results are similar to those found by Hinckley et al. High-Chromium White Cast Iron is a material highly used in mining and drilling shafts for oil extraction, due to its high wear resistance. Upon cooling, the austenite matrix becomes martensite because of the secondary carbide precipitation.

Austempered ductile cast irons

It can also be observed that the secondary chromium carbides MC and MC nucleated and grew within the dendritic matrix. 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 High 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. Gates, “The role of secondary ahstenita precipitation on the fracture toughness of a reduced carbon white iron”, Mater.

It was determined that the matrix structure is predominantly austenite austenite dendrites proeutecticwith an approximate 1. Also, the secondary carbides are distributed more homogeneously in the treated microstructures than in the as-cast one, this behavior was also found by Wang et al.

The XRD analysis revealed the presence of austenitic peaks, but also ferrite and carbides, with a percentage of While it was considered that the presence of residual austenite in the microstructure causes volumetric retenda 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 [5].

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