17-7 PH Stainless (Type 631, UNS S17700)
The spring-and-sheet PH stainless — formable in the annealed condition, then transformed and aged to 185 ksi for springs, washers, clips and high-strength small fasteners.
What 17-7 PH is.
17-7 PH is a semi-austenitic precipitation-hardening stainless. In the annealed condition it is austenitic, soft and formable; a conditioning treatment and refrigeration or an intermediate heat treatment then transform it to martensite, and a final age brings it to 170 to 185 ksi. It is the standard PH alloy for springs, spring washers, retaining rings and formed hardware.
ASTM A1082 lists it for bolting in the RH950 and TH1050 conditions. We supply 17-7 washers, springs and small fasteners from certified A564 bar and strip.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | — | 0.09 |
| Manganese | Mn | — | 1.00 |
| Phosphorus | P | — | 0.040 |
| Sulfur | S | — | 0.030 |
| Silicon | Si | — | 1.00 |
| Chromium | Cr | 16.00 | 18.00 |
| Nickel | Ni | 6.50 | 7.75 |
| Aluminum | Al | 0.75 | 1.50 |
Values per ASTM A564/A564M-19a Table 1 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Condition | Treatment | Tensile strength, min (ksi) | Yield strength, min (ksi) | Elongation, min (%) | Reduction of area, min (%) | Hardness, min |
|---|---|---|---|---|---|---|
| RH950 | 1750 °F 10 min to 1 h, rapid cool; within 24 h cool to −100 °F, hold 8 h; warm; age 950 °F 1 h, air cool | 185 | 150 | 6 | 10 | 41 HRC / 388 HBW |
| TH1050 | 1400 °F 90 min, cool to 55 °F within 1 h, hold 30 min; age 1050 °F 90 min, air cool | 170 | 140 | 6 | 25 | 38 HRC / 352 HBW |
Values per ASTM A1082/A1082M-16(2021) Table 3 and ASTM A564/A564M-19a Table 4 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
| Condition | Solution treatment | Hardness, max |
|---|---|---|
| A (annealed) | 1900 ± 25 °F (1040 °C), water quench | 98 HRB / 229 HBW |
Values per ASTM A564/A564M-19a Table 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Specifications that apply.
How 17-7 PH ships from Houston.
- Spring washers, Belleville washers and retaining rings
- Springs and clips
- Small high-strength bolts and studs to A1082
- Certified A564 bar and A693 strip
17-7 PH fasteners we make.
Every item is manufactured to your drawing or standard in 17-7 PH, imperial or metric, with an EN 10204 3.1 certificate.
What is 17-7 PH?
Unlike 17-4 and 15-5, which are martensitic as solution treated, 17-7 PH is austenitic and ductile after its 1900 °F anneal. Two routes then convert it: the TH1050 treatment conditions the austenite at 1400 °F, cools it to 55 °F to transform to martensite and ages at 1050 °F; the RH950 route conditions at 1750 °F, refrigerates at −100 °F and ages at 950 °F for the highest strength. Because the alloy is formed soft and hardened afterwards, it dominates springs, washers and stamped hardware, and A1082 lists both conditions for bolting.
Testing, certification and marking
- Tensile and hardness tested per lot on the finished product
- A1082 marking 177 (177A for condition RH, 177B for TH1050) and manufacturer's identification and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
- Transformation and ageing cycle recorded on the certificate
17-4 PH Stainless (Type 630, UNS S17400)
The high-strength stainless — up to 190 ksi in H900, or 115 to 135 ksi with real toughness in the H1150 conditions — for pump shafts, valve stems, subsea and aerospace fasteners.
ASTM A564 bar · AMS 565915-5 PH Stainless (XM-12, UNS S15500)
17-4 PH strength with better transverse toughness — the premium PH stainless for forgings, pump shafts and aerospace and valve fasteners.