The influence of chemical composition with Cr/C ratio of 2∼10 and destabilization heat treatment on transformation characteristics of high chromium cast irons was investigated with dilatometer. Two series of compositions are used : a) in variation of Cr/C ratio from 2 to 10 with keeping constant of another alloying elements, b) 3%C-20%Cr and 3%C-7%Cr alloys with 1.5∼5%Ni, 1∼5%Mo and 0.5∼2.5%Si.
Transformation behaviors of high chromium cast irons are affected by the chemical composition, destabilization temperature and cooling rate. Martensite transformation temperature (M
S) rises both with lowering cooling rate and with increasing destabilization temperature for any composition. M
S remains almost unchanged and does not depend on the destabilization temperature, however, when cooling rate is slower than 1°C/min.
M
S rises with increase of Cr/C ratio for a given destabilzation temperature and cooling rate. Banitic transformation occurs for Cr/C ratio smaller than 5 when cooling rate is lower than 4°C/min. Conversely, there are only martensitic transformations for Cr/C ratio larger than 5. Microscopic examination can hardly distinguish martensite from bainitic structure, however, the hardness decrease largely with presence of banitic structure.
In additon to be affected by Cr/C ratio, M
S temperature increases with increase of Si content and decreases with increase of Ni content. The effect of Mo content is little on M
S temperature.
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