Selection summary
Overview
17-7 PH is a chromium-nickel-aluminum semi-austenitic precipitation-hardening stainless steel supplied in formable austenitic conditions and transformed and aged to develop high strength. Condition A, TH, RH, and cold-worked routes are not interchangeable; product form, transformation treatment, aging cycle, dimensional change, spring direction, and final properties must all be specified.
This page separates standard-oriented limits from typical reference data. Purchase acceptance comes from the ordered specification and certified material test report.
Names and systems
Identity & standards
Similar designations across ASTM, EN, JIS, and other systems are not automatically interchangeable. Product form and ordered standard control chemistry, properties, dimensions, condition, and testing.
Reference chemistry
Composition
| Element | Reference range | Why it matters |
|---|---|---|
| Chromium | 16.0–18.0% | Corrosion resistance |
| Nickel | 6.5–7.75% | Austenitic condition and transformation control |
| Aluminum | 0.75–1.50% | Precipitation hardening |
| Carbon | ≤ 0.09% | Strength and carbide control |
Concise grade-family reference only. Confirm every element limit against the current standard for the exact product ordered.
Condition matters
Reference properties
TH1050, RH950, CH900 and other routes produce different results
Cold work, transformation, aging, gauge, and test direction must be identified
Typical room-temperature engineering reference
Environment first
Corrosion behavior
Corrosion resistance is often compared with 304 in suitable conditions, while heat treatment and surface state still matter.
It is not selected as a universal chloride-resistant grade; springs and stressed parts need environment- and condition-specific review.
Temperature, concentration, deposits, crevices, stress, surface finish, cleaning, and fabrication quality can change service performance.
Service limits
Temperature & service
Service exposure must remain compatible with the selected aging condition and spring-stress relaxation requirements.
Delivery condition
Heat treatment & condition
17-7 PH starts in a specified formable condition and requires a defined transformation route followed by precipitation aging, such as TH1050, RH950, or a cold-work-based condition.
Condition A, transformed conditions, and cold-worked spring tempers have different dimensions, magnetic response, directionality, strength, and toughness; the complete route must remain traceable.
Process route
Fabrication
Form in the specified austenitic condition, then apply the defined transformation and precipitation-aging route while accounting for dimensional change.
Joining and heat treatment can locally change transformation response; production procedures and final testing must be qualified.
Magnetic response: Condition-dependent; transformed and aged martensitic structures are magnetic.
Decision boundaries
Comparisons & substitution
17-7 PH suits formed sheet, strip, wire, springs, diaphragms, and bellows where an austenitic starting condition is useful before high-strength aging.
17-4 PH and 15-5 PH use martensitic PH routes more typical of bar, forging, and machined parts; substitution requires a new form, heat-treatment, toughness, and corrosion review.
Where it is used
Applications
Ordering scope
Product forms & standards
Bars, shapes, forgings, and machined stock under the applicable PH stainless product standard with both starting and final condition stated.
Plate, sheet, strip, or wire under the form-specific standard, including transformation, cold-work, aging, direction, and final-property requirements.
Decision support
Selection guidance
Choose this grade when
- A formable sheet, strip, or wire condition must later develop high spring strength.
- The manufacturer can control cold work, transformation, aging, directionality, and final dimensional verification.
Review another grade when
- The order does not define the starting and final condition or the transformation route.
- Thick sections, heavy forgings, aggressive chlorides, or simple one-step aging favor another alloy system.
Before ordering
Procurement checklist
Name the governing product specification and edition, exact UNS designation, dimensions, tolerances, finish, and delivery or heat-treatment condition.
Require a traceable material test report and verify chemistry, mechanical tests, heat treatment, marking, and any supplementary examination against the purchase order.
State the service environment, design temperature, fabrication route, inspection plan, certification, packaging, and any regulatory or end-user approval before order release.
Traceable evidence