Heat Treatment of 17–4 PH Stainless Steel Produced by Binder Jet Additive Manufacturing (BJAM) from N 2 -Atomized Powder

A new approach of heat treating 17–4 PH stainless steel parts generated by Binder Jet Additive Manufacturing (BJAM) was developed. Age hardening of 17–4 PH usually consists of two steps: solution treatment followed by quenching and subsequent aging for precipitation hardening. For 17–4 PH, the solution treatment is done at 1050 °C for 30 min while the aging temperatures range from 480 °C to 760 °C with a duration of two to four hours. When using N 2 -atomized powder, BJAM of 17–4 PH followed by conventional H900 heat treatment results in an undesired reduction of hardness below 170 HV10 which is attributed to a microstructure displaying more than 30 vol% of retained austenite (RA). N originating from the powder atomization process stabilizes austenite and, therefore, suppresses the martensitic transformation during quenching down to room temperature. This contribution shows the effect of increasing the solution annealing time to max. 90 min as well as additional deep-cooling (DC) at −90 °C for 120 min on hardness, tensile properties, phase distribution and chemical composition of 17–4 PH specimens. By increasing the solution annealing time from 30 to 90 min and additional deep-cooling after quenching, the amount of RA can be reduced to less than 5%. In combination with conventional H900 aging, the hardness of the specimens increased well above 380 HV10, while over-aging (H1150M) caused the desired increase in ductility. The tensile properties achieved by the modified heat treatments involving prolonged solution annealing and deep-cooling, referred to as H900* and H1150M* in this study, are YS = 1081 ± 86, UTS = 1235 ± 9, A = 9.4 ± 3.3% and YS = 504 ± 18 MPa, UTS = 813 ± 20 MPa, A = 18.6 ± 1.3%, respectively.