P添加によるオーステナイト系焼結PHステンレス鋼の高強度化

概要

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Phosphorus and 0.1 wt% carbon were added to SUS304L powder compacts in order to strengthen the P/M austenitic stainless steels. Effects of phosphorus content on the sintering and age hardening behavior were in-vestigated, in association with the tensile properties of the compacts. The results are summarized as follows: Phosphorus can dissolve in austenitic matrix up to about 0.45 wt% at 1523 K. In the compacts containing over 0.45 wt% of phosphorus, a liquid phase is formed through eutectic reactions and remains during the sintering. This results in the densification of compacts and the pore rounding. Tensile strength of as-sintered compacts increases with an increase in phosphorus content to reach the peak of 470 MPa at 0.6 wt% P, because of the solid solution hardening and the promotion of sintering. Phosphorus addition over 0.6 wt% produces a large amount of eutectic microstructure which affects negatively to the improvement of strength. Tensile strength of 0.6 wt% P compact increases to 590 MPa by the aging at 1023 K for 30 ks. The relation between porosity (ε) and strength ratio of porous compacts to full density compact (σ/σ0) is expressed by (σ/σ0) =(1-ε)/(1+6ε) for the 0.6 wt% P compacts aged in optimum conditions.
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