There are three types of precipitation hardening stainless steels:
Semi-austenite 17-7pH contains about 17% Cr, 7.2% Ni and 1.2% Al. Typical heat treatments include solution treatment and quenching. At this point, the structure is still austenitic. Martensitic transformation is then achieved either by deep cooling at 75 ° C (103 ° F) or by severe cold working (over 70% deformation, usually by cold rolling or drawing). The Ni3Al intermetallic phase was precipitated by aging at 510℃(950 F). Then it reaches the yield stress level above 1400 MPa.
Austenitic A286 (ASTM 660 EN 1.4980) contains about Cr 15%, Ni 25%, Ti 2.1%, Mo 1.2%, V 1.3%, and B 0.005%.The structure remains austenitic at all temperatures.
Martensite 17-4 PH contains about 17% Cr, 4% Ni, 4% Cu and 0.3% Nb. Solution treatment at about 1040 ° C (1900 ° F), followed by quenching, produces a relatively ductile martensite structure. After aging at 475℃(887 F), Nb and Cu-rich phases were precipitated and their strength increased to over 1000 MPa. This superior level of strength is used in high-tech applications such as aerospace (non-metallic inclusions are often removed after remelting, thereby increasing fatigue life). Another major advantage of this steel is that, unlike tempering, the aging temperature can be applied to the (almost) finished product without deformation and discoloration.