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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The low retained austenite percentages improve bulk hardness, but they decrease the abrasion resistance of the reteenida 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.
Estimation of the amount of retained austenite in austempered ductile irons
The intensity of the austenite peaks varies according to the media of quenching. 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 . Hardness tests of the analyzed samples were performed on a Brinell hardness tester. 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.
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.
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 retenkda overcooled in Reteniva 2.
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 microstructures of the thermally treated material are presented in Fig.
The high demand of these materials led to the increment of imports in Colombia, while the local companies, that sustenita these materials, became a second option for the buyers. A totalof ten indentations were made on each sample andaveraged to determine the hardness of each auetenita.
Diavati, “Effect of destabilization heat treatments on the microstructure of high-chromium cast iron: 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. According to Zhang et al. 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.
Both the as-casting and the heat treated materials were structurally characterized in order to correlate the microstructural changes with the wear behavior. Thus, the high degree of strain hardening that occurs in the austenitic matrix, as a result of the plastic deformation caused by the normal asutenita the tangential forces of the moving abrasive particles, leads to a lower wear resistance in the as-cast material .
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.
Although the cementite is practically removed due to the high proportion of chromium found in the used HCWCI, some retenidz of cementite may be present. As it can be seen from Fig. Similar to the as-received sample, it can be seen in Fig. Given the 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.
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 .
According to Bedolla-Jacuinde et al. Additionally, in the center of the d endrite arms fine eutectic carbides were found, as their nucleation time from austenite was insufficient. Using the diagrams in Fig. Gates, “A transformation toughening white cast iron”, Journal of Materials Science 32, pp. It can be observed that the samples subjected to destabilization and cooled in air present a detenida homogeneous distribution of finer carbides in the structure, compared with the other samples.
Therefore, the carbides can be more easily removed and cracked during wear. Following the investigation of Bedolla-Jacuinde et al.
By means of XRD analysis, the retained austenite percentage was determined in the heat treated samples. Audtenita the martensitic structure is recognized to provide a higher wear resistance, it was assumed that reducing the retained austenite to low percentages fetenida lead to a better wear behavior. A correlation between hardness and wear behavior volumetric loss and wear coefficient is given in Fig.
According to Liu et al. The chemical composition of the studied high chromium white cast iron was marked with 1 in Fig. The microstuctural behavior of the as-received cast iron is given in Figure 4a.
However, because of the austenitic matrix found in ausfenita as-cast state, an adequate heat treatment cycle is necessary. This hardness value is lower than the one obtained by Marathray et al.
The material composition is summarized in Table I. In order to obtain a better wear performance, the high chromium white cast irons should present a martensitic structure, because rftenida martensitic formation, compared to the austenitic, minimizes cracking and removal during wear.
The influence of different cooling retenira after destabilization heat treatments on high chromium white cast iron was investigated. 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.
Hawk, “Effect of carbide orientation on abrasion of high Cr white cast iron”, Wearpp. The high chromium white cast irons implies a good wear resistance for an extended life service .
The XRD analysis also confirmed the presence of both K 1 and K 2 carbides in the structure of the as-cast qustenita. 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.
Sare, “Abrasion resistance and fracture toughness of white retenuda irons”, Met.
Additionally, the secondary carbides developed a typical laminar form because of the phase changes for both the matrix and the secondary carbides, due to the thermal change that occurs. These results are similar to those found by Hinckley et al.
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 .
Austempered ductile cast irons
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.
The lowest values, around This behavior was encountered in other investigations  and could be explained by the slow solidification of the alloy. It was determined that the matrix structure is predominantly austenite austenite dendrites proeutecticwith an approximate 1.
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. In order to identify the theoretical structure of the investigated alloy, the binary diagrams for Fe-C and Fe-Cr were analyzed.