Mechanical properties and corrosion resistances of P/M two-phase stainless steels with silicon

Influence of the addition of silicon on mechanical properties and corrosion resistances of P/M austenitic stainless steels was investigated by means of microstructural examinations, calorimetric analysis and x-ray analysis. Silicon addition to P/M austenitic stainless steels makes the sintering in the duplex structure of austenite ( gamma ) and ferrite ( alpha ) possible by the liquid phase sintering with a eutectic liquid. For example, addition of 4 mass% Si results in the formation of approx40 vol.% of ferrite. Tensile strength of sintered steels increases with increased silicon content, and the maximum strength (940 MPa) was obtained in the steel with 4 mass% Si which was sintered for 3.6 ks at 1623K. On the other hand, elongation of sintered steels tends to increase with rising sintering temperature. The maximum elongation (47.5%) was obtained in the steel with 2 mass% Si which was sintered for 3.6 ks at 1673K. The sintered steel with 2 mass% Si was found to have excellent corrosion resistance in a boiling solution of 65% HNO sub 3 : The corrosion rate of the steel was very small in comparison with the sintered SUS304L steel, but it was three times larger than that of a SUS304L steel produced by ingot metallurgy. However, further addition of silicon causes a decline in corrosion resistance probably due to a decrease in the green density.