The mechanical properties of 17-4 PH must be fully developed by age hardening from Condition A in order to reduce risk of failure and to take full advantage of the material’s capabilities.
17-4 PH is a martensitic precipitation hardening (age hardening) stainless steel that can provide both high strength and excellent corrosion resistance.
In the annealed (solution treated condition- Condition A) the density of this material is 0.280 lb/in^3.
H 900 density is 0.282 lb/in^3.
H 1075 density is 0.283 lb/in^3.
H 1150 density is 0.284 lb/in^3.
These changes in density values show that this alloy undergoes a volume contraction when it is hardened. This volume contraction is predictable and must be taken into account if you are trying to hold close tolerances.
The contraction factor for the change from Condition A to Condition H 900 ranges from 0.0004 to 0.0006 in/in or (mm/mm).
Hardening from Condition A to Condition H 1150 contracts in the range of approximately 0.0009 to 0.0012 in/ in or (mm/mm).
Here are three reasons to NOT use 17-4 PH in the Condition A state:
- The structure is untempered martensite. This means low fracture toughness.
- The structure is untempered martensite. This means low ductility.
- Without age hardening, this material is more susceptible to stress corrosion cracking.
17-4 PH martensitic stainless steel can achieve high strength and superior corrosion resistance when precipitation hardened from Condition A to one of the Condition H tempers. It is used in many high performance applications made by our industry including valve parts for oilfield and chemical plant use; Fittings for aerospace and aircraft use; Jet engine componentry; Fasteners; Shafts for pumps; Dodge Viper carburetors! Many others.
In applications where high performance is mandatory, it is also mandatory to follow needed thermal treatment practices to assure the development of the full range of material properties that the material can provide.
For the savvy machinist, that also means understanding the pootential effect of that thermal treatment on final size due to dimensional contraction when hardened.
Thanks to Bouchillon for the throttle photo.
Material on Dimensional Contraction was taken from Schmolz + Bickenbach 17-4 Datasheet.
Density and European Equivalency data from Rolled Alloys data sheet.
European designation note: Officially 17-4 PH is designated as UNS S17400. It is the US available nominal equivalent to DIN 1.4548, X5CrNiCuNb 17-4-4