Homogenization timing effect on microstructure and precipitation strengthening of 17–4PH stainless steel fabricated by laser powder bed fusion

Aging Behaviour of a 12.2Cr-10Ni-1Mo-1Ti-0.6Al Precipitation-Hardening Stainless Steel Manufactured via Laser Powder Bed Fusion

“…On the other hand, specimens solution annealed at 925 • C and quenched (S) exhibited a homogeneous, not-oriented martensite microstructure with no trace of melt pool boundaries, oriented grains, or a cellular solidification sub-structure (Figure 2b,d and Figure 3b,d). In fact, solution annealing induces alloying diffusion and the transformation of martensite in austenite with a subsequent recrystallization, thus removing the cellular substructure and leading to the nucleation of equiaxed prior austenite grains of homogeneous composition, from which a non-oriented martensite microstructure forms upon rapid cooling [19,[21][22][23][25][26][27][28]. XRD analyses (Figure 4) indicated a very low γ-austenite content in not-aged samples, which was slightly higher for AB (2.95 vol.%) than for S (1.94 vol.%).…”

“…PH-SS are easily manufacturable by LPBF due to their low C content, leading to a reduced risk of crack formation [14,[16][17][18]. The as-built (AB) microstructure of LPBF-manufactured PH-SS consists of melt pool/scan track boundaries, a martensite microstructure with oriented grains, and a cellular solidification sub-structure, and exhibits relatively low hardness and strength due to the lack of strengthening precipitates comparable to condition A for conventionally manufactured PH-SS [8,14,17,[19][20][21][22][23][24][25][26][27][28][29][30]. The AB microstructure of Cu-bearing 17-4 PH and 15-5 PH steels can possess significant amounts of metastable, retained γ-austenite, depending on the powder atomisation and LPBF inert gas atmosphere [18,[31][32][33][34][35][36][37][38][39][40].…”