Effect of powder loading on metal injection molding stainless steels

Powder loading is one of the most critical factors which has important influence on metal injection molding processes. Using the gas atomized spherical 17-4 PH stainless steel powder and the binder of 65% PW + 30% EVA + 5% SA, four kinds of feedstocks were prepared at the powder loading of 60, 64, 68 and 72%, respectively. The effects of the powder loading on the feedstock rheological properties, the compact distortion and tolerance control as well as mechanical properties and microstructures were investigated. It is proved that 68% powder loading is the optimal one. The feedstock with 68% powder loading can be injection molded with a comparatively low viscosity on a relatively wide temperature range, and it is best to get quick powder re-packing and binder molecule orientation during injection molding. From the standpoint of compact shape retention and dimension tolerance control, the optimal powder loading of 68% is also the best. Furthermore, the compact of 68% powder loading is easy to get sinter densification and has superior mechanical properties and microstructures.