Binder Jetting – Influence of shell printing on sintering densification and microstructure of 17-4 PH stainless steel

The shell printing strategy was utilized for Binder Jetting of 17-4 PH stainless steel to investigate the impact of the binder on green density, sintering densification, phase transformations and microstructure gradients. Green parts with 25%, 50%, 75% and 100% shell volume were printed and sintered in a dilatometer under Ar and H 2 atmospheres. The green density increased from 4.46 g/cm 3 for 25% shell volume to 4.82 g/cm 3 for 100% shell volume due to binder-induced particle rearrangement. The sintering densification in H 2 was primarily influenced by the powder packing, as higher shrinkages compensated for lower green densities, resulting in comparable sintered densities between 99.7% and 99.9%. Debinding in H 2 ensured low sintered carbon levels, resulting in high δ-ferrite fractions during sintering and martensite formation during cooling. In contrast, sintering in Ar was mainly impacted by carbon introduced by the binder since debinding efficiency was low. The increasing shell volume reduced the δ-ferrite fractions during sintering due to carbon pickup, which decreased the sintered densities from 99.3% for 25% shell volume to 93.4% for 100% shell volume. The binder-free core exhibited less porosity, higher microhardness and higher δ-ferrite fractions than the binder-affected shell, as carbon pickup stabilizes austenite during sintering and cooling.