The precipitation-hardening stainless steels are iron-nickel-chromium alloys containing a number of precipitation hardening elements such as aluminum, titanium, copper mineral, niobium, and molybdenum. The precipitation hardening is gained by a relatively simple aging take care of the created part. http://vattu24h.net
Both main characteristics of all precipitation-hardening metal steels are hi-strength and high corrosion resistance. Great strength is, unfortunately, achieved at the expense of toughness. The corrosion level of resistance of precipitation-hardening stainless terme conseillé is just like that of the standard AISI 304 and AISI 316 austenitic metals. The aging treatments are made to optimize strength, corrosion level of resistance, and toughness. To improve toughness, the amount of carbon is kept low.
The first commercial precipitation-hardening stainless steel was developed by US Steel in 1946. The alloy was named Stainless W (AISI 635) and its nominal chemical composition (in wt. %) was Fe-0. 05C-16. 7Cr-6. 3Ni-0. 2Al-0. 8Ti.
The precipitation hardening process involves the organization (precipitation) of very fine intermetallic phases such as Ni3Al, Ni3Ti, Ni3(Al, Ti), NiAl, Ni3Nb, Ni3Cu, carbides, and Laves (AB2) phases. Long term aging causes the coarsening of these intermetallic stages, which in turn triggers the decline in power, due to the simple fact that dislocations can circumvent coarse intermetallic phases.
Right now there are three types of precipitation-hardening stainless steels:
– Martensitic precipitation-hardening stainless terme conseillé, e. g., 17-4 PH LEVEL (AISI 630), Stainless Watts, 15-5 PH, CROLOY 16-6 PH, CUSTOM 450, TAILOR MADE 455, PH 13-8 Mo, ALMAR 362, IN-736, and so on., – Austenitic precipitation-hardening metal steels, e. g., A-286 (AISI 600), 17-10 S, HNM, etc., and – Semiaustenitic precipitation-hardening stainless terme conseillé, e. g., 17-7 PH LEVEL (AISI 631), PH 15-7 Mo, AM-350, AM-355, PH LEVEL 14-8 Mo, and so forth
The type is determined by the martensite start and the martensite finish temperature (Ms and Mf) as well as the as-quenched microstructure.
Throughout the heat treatment of precipitation-hardening stainless steels, regardless of their type, austenitization in the single-phase austenite region is always the first thing. Austenitization is then followed by a comparatively speedy cooling (quenching).
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 LEVEL, CUSTOM 450, CUSTOM 455, PH 13-8 Mo, ALMAR 362, and IN-736 – is merely above room temp. Thus, after quenching from the solution-treatment temperature they transform completely into martensite. Precipitation hardening is achieved by just one aging treatment at 480? C to 620? C (896? N to 1148? F) for 1 to 4 several hours.
The martensite start heat (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 after quenching.