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Precipitation hardening stainless steel

The precipitation hardened (PH) stainless steel grades can be subdivided into martensitic, semi-austenitic, and fully austenitic grades. Because of their higher chromium levels, the PH grades have better corrosion resistance than the martensitic stainless steels and are used for high strength applications that require more corrosion resistance. Common applications for the PH grades include fasteners, aircraft fittings, shafts, gears, bellows, and jet engine parts.

Martensitic PH stainless steels: This group of stainless steels includes the 17-4PH® (S17400), 15-5 PH® (S15500), 13-8 PH® (S13800), Custom 450® (S45000), and Custom 455® (S45500) grades.  With the martensitic PH grades an un-tempered martensitic microstructure is produced during cooling from the solution anneal temperature. A subsequent age-hardening heat treatment between 480 and 620°C (900 and 1150°F) results in a fine dispersion of precipitates and tempers the martensite structure to achieve the desired level of strength, toughness, and ductility. The martensitic PH grades are well suited for bar, wire, and forging applications.

Semi-austenitic PH stainless steels: The semi-austenitic grades have a balanced composition that results in a solution-annealed microstructure that is predominately austenite phase. This more ductile structure can then be formed using standard techniques. After fabrication, a thermal treatment is used to transform the austenite to martensite followed by an aging heat treatment, which increases the strength due to precipitation. Common semi-austenitic PH grades include 17-7PH® (S17700), 15-7 PH® (S15700), AM-350® (S35000), and AM 355® (S35500). The semi-austenitic PH grades are used primarily for flat-rolled applications and applications that require extensive forming.

Austenitic PH stainless steels: The A286 (S66286) grade is the only PH grade that remains primarily austenitic after the aging heat treatment. The A286 grade is hardened after solution annealing by a one-step aging heat treatment to precipitate Gamma Prime phase. The A286 grade is used in applications that require high strength and good corrosion resistance at temperatures up to 700°C (1300°F). Common uses include jet and automotive engine components, gas turbine blades, high temperature fasteners, and springs.

Chemical Composition* (weight%) of some common precipitation hardened stainless steels**
Common Name UNS Number EN No


Mn Si Cr Ni Mo Other
Martensitic PH Stainless Steels
PH 13-8 Mo S13800 1.4534 0.05 0.20 0.10 12.25-13.25 7.5-8.5 2.00-2.50

Al 0.90-1.35

N 0.10

15-5 PH S15500 --- 0.07 1.00 1.00 14.0-15.5 3.5-5.5

Cu 2.5-4.5

(Nb+Ta) 0.15-0.45

17-4 PH S17400 1.4542 0.07 1.00 1.00 15.0-17.5 3.0-5.0

Cu 3.0-5.0

(Nb+Ta) 0.15-0.45

Custom 450 S45000 --- 0.05 1.00 1.00 14.0-16.0 5.0-7.0 0.50-1.00

Cu 1.24-1.75

Nb 8xC min.

Custom 455 S45500 --- 0.05 0.50 0.50 11.0-12.5 7.5-9.5 0.50

Ti 0.9-1.4, Cu 1.5-2.5

(Nb+Ta) 0.1-0.5

Semi-Austenitic PH Stainless Steels
PH 15-7 Mo S15700 1.4532 0.09 1.00 1.00 14.0-16.0 6.50-7.75 2.00-3.00 Al 0.75-1.50
17-7 PH S17700 --- 0.09 1.00 1.00 16.0-18.0 6.50-7.75 Al 0.75-1.50
AM-350 S35000 --- 0.07-0.11 0.50-1.25 0.50 16.0-17.0 4.0-5.0 2.50-3.25 N 0.07-0.13
AM-355 S35500 --- -0.10-0.15 0.50-1.25 0.50 15.0-16.0 4.0-5.0 2.50-3.25 N 0.07-0.13
Austenitic PH Stainless Steels
A-286 S66286 1.4980 0.08 2.00 1.00 13.5-16.0 24.0-27.0 1.0-1.5

Ti 1.90-2.35, Al 0.35 max,

V 0.1-0.5, B 0.003-0.010


* Taken from ASTM specifications for plate, sheet and strip when available or from company data sheets. For complete compositional requirements consult these sources.
** Chemistry maximum, unless range or minimum is indicated, EN chemistry does not correspond exactly to ASTM chemistry