Masatomo Kamada1 and Youichi Tokunaga1
1Department of Materials Science and Engineering, Faculty of Engineering, Kyushu University, Fukuoka
The relationship between sintering shrinkage and phase constitution was investigated for (δ/γ ) two phase stainless steel compacts made of equilibrium powders. The chemical compositions of the δ and γ powders were controlled to Fe-27 mass%Cr-7 mass%Ni and Fe-20 mass%Cr-12 mass%Ni, respectively, which were equilibrium compositions at 1473 K, in order to suppress the chemical diffusion of atoms between the powders.
The sintering shrinkage rate of the compacts increases with an increase in the amount of δ powder owing to the high self-diffusivity of atoms in δ phase. There are some differences in shrinkage rate, however, between the experimental results and the value calculated in proportion to the volume fraction of each phase.
In compacts containing small volume of δ powder, the experimental shrinkage becomes smaller than the calculated value, because the sintering is controlled by the diffusion of atoms in γ phase. On the other hands, the experimental shrinkage of the compacts containing large volume fraction of δ becomes larger than the calculated value, because the sintering depends upon the diffusion of atoms in δ phase.
Significant grain growth occurs in δ single phase compacts and this prevents the transgranular pores disappearing during the final stage of sintering. since the grains grow slightly in (δ/γ) two phase compacts, the (δ/γ) compacts containing large volume of δ shrink larger than δ single phase compacts with incerasing sintering time.
sintering, equilibrium phase, austenite, δ-ferrite, two phase stainless steel, linear shrinkage
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