Impact of oxygen content on debinding of binder jetted 17-4 PH stainless steel: Part II – Sintering

Binder jetting requires the sintering of green parts to reach the properties of a metallic component. The sintering activity and sintered material properties of stainless steels are sensitive to powder oxidation and binder contamination, which are introduced by improper debinding. Air is often used during thermal debinding as oxygen aids binder removal, but the metal powder is oxidised being detrimental to sintering densification and final material properties. Hence, the impact of decreasing oxygen content in the debinding atmosphere on the sintering of 17-4 PH at 1300°C for 2 h in an inert argon atmosphere was investigated. Debinding in oxygen-containing atmospheres revealed the presence of δ-ferrite in the sintered microstructure, enhancing densification during sintering. Debinding in an inert Ar atmosphere resulted in low densification that was correlated to the absence of δ-ferrite due to the high amount of carbon in the sintered part. The high carbon content after debinding in Ar resulted in nearly complete oxygen removal by carbothermal reduction during sintering. Debinding in Ar + 1 vol.% O 2 achieved the best combination of reducing final oxygen content by 46% via carbothermal reduction and the absence of carbon pickup during debinding and sintering. Debinding in processing atmospheres containing 3 vol.% O 2 up to 20 vol.% O 2 , in contrast, led to a significant oxygen increase of 53 to 74% after sintering compared to the virgin powder.