AUSTENITA RETENIDA PDF

Tajinn The microstructures of the thermally treated material are presented in Fig. A correlation between hardness and wear behavior volumetric loss and wear coefficient is given in Fig. 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. Similar to the as-received sample, it can be seen in Fig.

Author:Teran Fesho
Country:Colombia
Language:English (Spanish)
Genre:Art
Published (Last):20 November 2010
Pages:272
PDF File Size:20.83 Mb
ePub File Size:14.29 Mb
ISBN:753-2-69844-189-7
Downloads:44139
Price:Free* [*Free Regsitration Required]
Uploader:Tujar



Jugore Austempered ductile cast irons 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]. In order to identify the theoretical structure of the investigated alloy, the binary diagrams for Fe-C and Fe-Cr were analyzed.

However, the diffraction when quenching in oil is run to the left and presents interferences. 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. As it can be seen from Fig. The influence of different cooling media after destabilization heat retejida on high chromium white cast iron was investigated.

The XRD analysis revealed the presence of austenitic peaks, but also ferrite and carbides, retebida a percentage of 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.

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. During the heat treatment, the ferrous matrix is supersaturated with carbon and chromium leading to the precipitation of secondary carbides.

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 austeniya C 6 nucleated and grew within the dendritic matrix.

Following the investigation of Bedolla-Jacuinde et al. Therefore, a certain minimum percentage of retained austenite is required in order to provide the best wear performance. To ensure therepeatability of the test and to reduce the error in their results, five samples were used. 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].

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. 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.

Hardness tests of the analyzed samples were performed on a Brinell hardness tester. The microstructures of the thermally treated material are presented in Fig. It should be noted that in the analyzed materials, the a phase is mainly associated to the ferrite phase. This hardness value is lower than the one obtained by Marathray et al. According to the literature, the microstructure of the high-chromium white cast irons, influences the wear behavior. 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.

This increased hardness could be the result of the precipitation of secondary carbides, which destabilized the austenite leading ausstenita 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]. 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.

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 retenisa activation provided by heat treatment allows precipitation of chromium carbides [12, 13]. The results show that although air cooling followed by immersion in Audtenita 2 can effectively reduce the retained austenite, this is not refenida to transform completely the retained austenite into martensite.

Upon cooling, the austenite matrix becomes martensite because of the secondary carbide precipitation. 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.

Both the as-casting and the heat treated materials were structurally austemita in order to correlate the microstructural changes with the wear behavior. The high chromium white cast irons implies a good wear resistance for an extended life service [1]. Related Articles.

SCHOOL OF CHESS EXCELLENCE BY MARK DVORETSKY PDF

AUSTENITA RETENIDA PDF

Volkis The resulting carbide percentage was around 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. The chemical composition of the studied high chromium white cast iron was marked with 1 in Fig. 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. 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].

AMEIVA UNDULATA PDF

Dougor 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.

Related Articles