Abstract
The excellent abrasion resistance of high-chromium cast irons (HCCIs) is given by an optimal combination of hard eutectic and secondary carbides (SC) and a supporting matrix. The tailoring of the microstructure is performed by heat treatments (HTs), with the aim to adjust the final properties (such as hardness and abrasion resistance). In this work, the influence of chemical composition on the microstructure and hardness of HCCI_26%Cr is evaluated. An increase in the matrix hardness was detected after HTs resulting from combining precipitation of M23C6 SC during destabilization, and austenite/martensite transformation during quenching. Kinetic calculations of the destabilization process showed that M7C3 secondary carbides are the first to precipitate during heating, reaching a maximum at 850 °C. During subsequent heating up to 980 °C and holding at this temperature, they transformed completely to M23C6. According to the MatCalc simulations, further precipitation of M23C6 occurred during cooling, in the temperature range 980–750 °C. Both phenomena were related to experimental observations in samples quenched after 0-, 30-, 60- and 90-min destabilization, where M23C6 SC were detected together with very fine SC precipitated in areas close to eutectic carbides.
Highlights
High-chromium cast irons (HCCIs) are used for wear-resistant components in the mining and mineral processing industries, given their outstanding wear and erosion resistance.[1]
high-chromium cast irons (HCCIs) can be considered as composite materials, showing a structure composed of large eutectic M7C3 (M: Cr–Fe) carbides embedded in a softer ferrous matrix, which could be austenitic in the as-cast condition or martensitic after a subsequent thermal treatment.[2,3]
The SCD sample was subjected to a destabilization, followed directly by a sub-critical diffusion step and slow cooled until room temperature
Summary
High-chromium cast irons (HCCIs) are used for wear-resistant components in the mining and mineral processing industries, given their outstanding wear and erosion resistance.[1]. Distributed throughout the metallic matrix.[4] the presence of secondary carbides has shown to improve the wear resistance behavior of the whole ‘‘composite.’’5 the properties of the material are dependent upon the volume fraction, size and distribution of the second phase,[6] and especially of the SC precipitated during thermal treatment. This controlled precipitation improves the mechanical properties of HCCI, mainly those related to friction reduction and abrasive wear resistance.[7,8,9]. The microstructure in HCCI can be modified through alloy design, processing route and heat treatments (HTs), which can include destabilization, sub-critical and quenching treatments, or a combination thereof.[10,11] An optimal destabilization process is highly dependent on the temperature (900–1150 °C) and holding time (5 min to 8 h), and the used parameters together with the chemical
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