Effects of residual carbon content on sintering shrinkage, microstructure and mechanical properties of injection molded 17-4 PH stainless steel

摘要

Carbon contamination from the thermoplastic binder is an inherent problem with the metal powder injection molding process. Residual carbon in the compacts after debinding has a strong impact on the sintering process, microstructure, and mechanical properties. In this study, injection molded 17-4 PH stainless steel was debound to two levels of residual carbon, 0.203 +/- 0.014 wt% and 0.113 +/- 0.008 wt%, by elevating the debinding temperature from 450degreesC to 600degreesC. Dilatometry in H-2 atmosphere shows that the 600degreesC-debound compacts shrink much faster than those debound at 450degreesC when the sintering temperature rises to over 1200degreesC. Density measurements for tensile bars sintered between 1260degreesC and 1380degreesC confirm the beneficial effect of low residual carbon content on sintering shrinkage. Quantitative metallography reveals that more delta-ferrite forms along austenite grain boundaries during sintering of the 600degreesC-debound compacts. In both samples, density gradients across the compact section are correlated with the residual carbon content and corresponding delta-ferrite formation. Finally, tensile tests show that the 600degreesC-debound compacts have lower tensile strength but higher ductility than those debound at 450degreesC. The relevant mechanisms are discussed with a focus on the effects of residual carbon content, delta-ferrite amount, and porosity. (C) 2002 Kluwer Academic Publishers. [References: 24]