Martensitic Precipitation-Hardening Stainless Steel
During the heat treatment of precipitation-hardening stainless steels, regardless of their type, austenitization in the single-phase austenite region is always the first step. Austenitization is then followed by a relatively rapid cooling (quenching).
The martensite finish temperature (Mf) of the martensitic precipitation-hardening stainless steels — such as 17-4 PH (AISI 630), Stainless W, 15-5 PH, CROLOY 16-6 PH, CUSTOM 450, CUSTOM 455, PH 13-8 Mo, ALMAR 362, and IN-736 — is just above room temperature. Thus, upon quenching from the solution-treatment temperature they transform completely into martensite. Precipitation hardening is achieved by a single aging treatment at 480 °C to 620 °C (896 °F to 1148 °F) for 1 to 4 hours.
The martensite start temperature (Ms) of the martensitic precipitation-hardening stainless steels is required to be above room temperature in order to ensure a full martensite-to-austenite transformation upon quenching.
One of the empirical equations that is often used to predict the martensite start temperature (in °F) is as follows:
Ms = 2160 – 66·(% Cr) – 102·(% Ni) – 2620·(% C + % N)
where Cr = 10-18 %, Ni = 5-12.5 %, and C + N = 0.035-0.17 %.
Precipitation hardening in the martensitic steels is achieved by reheating to temperatures at which very fine intermetallic phases — such as Ni3Al, Ni3Ti, Ni3(Al,Ti), NiAl, Ni3Nb, Ni3Cu, carbides, and Laves phase — precipitate.
A lath martensite structure provides an abundance of nucleation sites for the precipitation of intermetallic phases.
To cover the costs of running this site, we accept consulting assignments to perform customer tailored Thermo-Calc and DICTRA calculations. If we cannot solve your problem, we will help you find at least one organization which has the right human and computational resources to address your specific needs.
We offer a money back guaranty for our consulting services if you are not satisfied. Drop us a line; our e-mail address is: firstname.lastname@example.org.