抄録
The effects of the addition of boron (B) and silicon (Si) on mechanical properties of P/M SUS630 stainless steels were investigated. As a result, the addition of B is effective to the densification of microstructure, and the maximum relative sintered density (98.2%) is obtained in the P/M steel with 0.2mass%B sintered at 1573 K. By the simultaneous addition of B and Si, the sintering temperature obtained the maximum density is lower than that of the single addition of B about 50 K. The addition of Si is effective to obtain high strength and hardness. This may be due to the solid solution strengthening by Si to the matrix. But the excessive addition of Si (over 2 mass%) makes the P/M steels brittle. Tensile strength and Rockwell hardness of P/M steels with 0.2mass%B and lmass%Si, which was sintered at 1523 K and heat treated, were 1230MPa and 43HRC respectively. These values of the P/M steel are similar to those of wrought SUS630 steel. On the other hand, the ductility was not improved by the addition B and Si. This result may be due to grain coarsening, precipitation of borides and hardening of matrix by Si during liquid phase sintering.
