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    Effect of Mg–Re complex treatment on eutectic carbides in bearing steel
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    Abstract:
    Effect of an Mg–Re complex treatment on eutectic carbides in bearing steel has been studied. Results show that the number, and the average maximum size of carbides tend to decrease and then increase with the increase in Mg content. When the Mg content is low, the addition of Re is not conducive to the refinement of carbides; When the Mg content is high, the number and size of carbides decreases with the increase of Re. The main reason for the refinement of carbides by Mg is that the diffusion of Mg hinders the diffusion of C and Cr, so that the formation and growth of carbides are inhibited. A large number of MgS-MnS can induce the precipitation of carbides, which also leads to the dispersion of carbides. While the Re‑Mg complex treatment, the inclusions containing Re and segregation of Mg is the main reason for the refinement of carbides.
    Aimed at the eutectic carbides distributed at network shape in the cast iron,the effect of heat treatment on morphology of eutectic carbides in low alloy wear resistant cast iron after deformation was studied.The results show that the morphology and distribution of eutectic carbides in the cast iron improve by high temperature heat treatment and hot deformation,and the morphology of eutectic carbides is changed from continuous network into streaks and blocks;the network eutectic carbides are transformed into streaky and blocky carbides when the cast iron after 20% hot deformation is treated at 970℃ for 3 h.
    Morphology
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    The influence of heating temperature in annealing treatment on morphology of eutectic carbide in twin roll casting strip of high speed steel was studied. The results of experiment indicate that network eutectic carbides keep on being dissolved and broken up with increasing of heating temperature. The granular carbides are increased gradually. Network eutectic carbides are transformed into granular carbides when heating temperature is up to 950?℃. The results of experiment were analyzed by means of Thompson Friedrich equation and it is shown that the reduction of eutectic spacing offers the suitable condition for eutectic carbides to being dissolved and granulated.
    High Speed Steel
    Citations (1)
    Effects of different heating temperature and holding time on the decomposition behavior of M2C eutectic carbide in M2 high speed steel were investigated by SEM and EDS.The results show that the degree of decomposition of M2C eutectic carbide is increased with the increase of heating temperature and holding time,but the heating temperature plays a main role.The process of decomposition of M2C eutectic carbide was discussed.The characteristics of decomposition are that the decomposition of M2C eutectic carbide is controlled by the diffusion behavior of atoms;the M6C carbides form in the outer layer of the original M2C eutectic carbide and the MC carbides form in the inner layer.
    High Speed Steel
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    Carbides in HSS roll were studied systematically. The results showed that there were two kinds of carbides in HSS roll, 1st and 2nd carbides. 1st eutectic carbides included the chrysanthemum-like MC mainly consisting of V and the plate-like M2C rich in Mo. 2nd carbides were complex carbides, concentrating Fe, Cr, Mo and V elements. The morphology, distribution and alloy concentration of the 1st eutectic carbides were studied using OM, SEM and EDS. During heat treatment, evolution of the 1st eutectic carbides was analyzed. It was found that the MC carbides had no change in morphology, components and distribution, while the M2C carbides decomposed to M6C and MC. In order to improve the properties of HSS, a method of increasing solidification rate was defined to refine the eutectic carbides. After refinement, the eutectic carbides distributed both along the grain boundaries and inside the grains.
    High Speed Steel
    Some of the wear-resistant tools or coatings are based on Ni, Co or Fe and contain very high carbon contents for promoting high volume fractions of carbides in the microstructures.Among them fine eutectic carbides and coarse pro-eutectic carbides do not induce the same properties for the alloys in terms of hardness, wear resistance and impact toughness. Thus itmay be important to knowinwhich proportions they are in the eutectic formand as coarse carbides. Eighteen 30wt.%-containing nickel-based, cobalt-based and iron-based alloys with six different carbon amounts (from2.5 to 5.0wt.%) previously elaborated by high frequency induction melting were metallographically characterized in their as-cast condition and after heat-treatments at high temperature. More precisely their microstructures were quantified by image analysis in order to separate the surface fractions of the pro-eutectic phases (dendrites of matrix or carbides) fromthe eutectic compound. These results were thereafter compared to the ones issued from Thermo-Calc calculations concerning the eutectic solidification part.
    Carbon fibers
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    Aimed at the problem that eutectic carbides in low alloy white cast iron are distributed with reticulation shape, the effect of heat treatment on morphology of eutectic carbides in low alloy white cast iron after deformation was studied. The results showed that the morphology and distribution of eutectic carbides in the cast iron were improved by high temperature heat treatment and hot deformation, and the morphology of eutectic carbides is changed from continuous reticulation into strip and block. When the cast iron after 20% hot deformation is treated at 970 ℃ for 3 h, stripy and blocky carbides will replace reticular eutectic carbides, and the impact toughness is improved by 88.56%.
    Morphology
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