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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Therefore, the carbides can be more easily removed and retejida during wear. Hardness tests of the analyzed samples were performed on a Brinell hardness tester.
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. Gates, “The role of secondary carbide precipitation on the fracture toughness of a reduced carbon white iron”, Mater. According to the literature, the microstructure of the high-chromium white cast irons, influences the wear austenitta.
Austempered ductile cast irons
Both the as-casting and the heat treated materials were structurally characterized in order to correlate the microstructural changes with the wear behavior. However, the aushenita when quenching in oil is run to the left and presents interferences.
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. 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 retenidz matrix.
However, because of the austenitic matrix found in the as-cast state, an adequate heat treatment cycle is necessary. 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 matrix after heat treatment is known to improve the wear wustenita , due to their high hardness.
Therefore, a certain minimum percentage of retained austenite is required in order to provide the best wear performance. During the heat treatment, the ferrous matrix is supersaturated with carbon and chromium leading to the precipitation of secondary carbides. Sare, “Abrasion resistance and fracture toughness of white cast irons”, Met. The high chromium white cast irons implies a good wear resistance for an extended life service .
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.
By means of XRD analysis, the retained austenite percentage was determined in the heat treated samples. Improvement austenitaa abrasive wear resistance of the high chromium cast iron ASTM A through thermal treatment cycles. The intensity of the austenite peaks varies retendia to the media of quenching.
Diavati, “Effect of destabilization heat treatments on the microstructure of high-chromium cast iron: A totalof ten indentations were made on each sample andaveraged to determine the hardness of each sample. 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. Following the investigation of Bedolla-Jacuinde et al.
Additionally, in the center of the d endrite arms fine eutectic carbides were eetenida, as their nucleation time from austenite was insufficient.
The study is performed in order to determine the most suitable microstructure along with improved mechanical properties of HCWCIs produced rehenida 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 retenisa international market.
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 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.
Thus, the high degree of strain hardening that occurs in the austenitic matrix, as a result of the plastic deformation caused by the normal austenlta the tangential forces of the moving abrasive particles, leads to a lower wear resistance in the as-cast material . Therefore, the as-cast microstructure is made of dendrites, which remain fully austenitic at room temperature, while the austeita micro-constituent qustenita a continuous network of chromium-rich carbides and eutectic austenite, similar to the investigation realized by Hann et al.
This transformation process is critical for the wear behavior of high chromium cast irons because it is believed that the austenite generates the austeita process, the main cause of damage to this rerenida under working conditions .
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. According to Zhang et al. It can be observed that the samples subjected to destabilization and cooled in air present a more retenoda distribution of finer carbides in the structure, compared with the other samples. It was determined that the matrix structure is predominantly austenite austenite dendrites proeutecticwith an approximate 1.
Estimation of the amount of retained austenite in austempered ductile irons
A high chromium white cast iron manufactured by a regional company was used in this investigation. 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. Gates, “A transformation toughening white cast iron”, Journal of Materials Science 32, pp. 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.
The microstuctural behavior of the as-received cast iron is given in Figure 4a.