Effect of ferritic grain size on the structure and growth of austenitic colonies during cementation of chromium steels
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The fixed growth of the austenite-carbide colonies during carbonization of chromium alloys is prevented close to the grain boundaries of the initial ferrite. Restructuring of the colonies under various conditions is associated with diffusion of carbon and chromium in the ferrite and the creation of a thermodynamically unstable martensitic phase ahead of the recrystallization front, which is supersaturated with chromium and carbon. Thus, in the initial stages of growth, as the degree of supersaturation in the ferrite increases, lamellar rod-shaped colonies grow whose main growth direction is along the carbon concentration gradient. A decrease in the supersaturation of carbon in the ferrite as one moves away from the advancing front toward the center of the grain makes the isolated growth of the coarsely agglomerated phase along the boundaries of the initial ferritic grains possible. The less the amount of defects in the grain boundaries, the more the body of the ferritic grains becomes supersaturated. This leads to the simultaneous growth of the new phase at some distance from the general growth front of the colonies.
KeywordsChromium Ferrite Recrystallization Supersaturation Carbon Concentration
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