The effect of Sinter process on the property of low expansion alloys of powder injection molding

The effects of sintering process on the properties of 4J32 low expansion alloys by powder injection molding were investigated. The results show that the relative density and the grain size of alloys increase with the sintering temperature or time. The properties of the alloy will be improved by sintering in atmosphere of hydrogen or high vacuum. After sintering under the optimum conditions, i.e. at temperature 1350 degrees C in atmosphere of hydrogen for 120 min, the PIM 4J32 low expansion alloys with high properties are obtained, which the relative density is 98.3% and the average thermal expansion coefficients below 100 degrees C is 0.3 x 10(-6) K-1. The expansive property is better than that of alloys manufactured by traditional methods or GB specification. The microstructure of alloys is constituted of an., austenitite gamma phase and a little martensite alpha phase.