COMPREHENSIVE TECHNICAL ANALYSIS AND DATASHEET OF 17-7 PH (UNS S17700) FASTENING SYSTEMS
17-7 PH (Precipitation Hardening), also known as UNS S17700 or Type 631, is a highly advanced semi-austenitic precipitation-hardening stainless steel. Unlike its martensitic cousins (17-4 and 15-5), 17-7 PH remains austenitic in its annealed state (Condition A), granting it the excellent formability and workability of standard 300-series stainless steels. Upon undergoing complex heat treatments or severe cold working, its structure transforms to martensitic, allowing for extraordinary strength levels during the final aging process.
Utilizing Aluminum (Al) as its primary precipitation-hardening agent rather than Copper, 17-7 PH provides immense yield strength, excellent fatigue properties, and good corrosion resistance. It is uniquely suited for high-strength springs, aerospace retaining rings, belleville washers, and specialized heavy-duty fastening systems operating in temperatures up to 600°F (316°C).
■ Product Overview & Specifications
17-7 PH requires a highly controlled, multi-step thermal processing cycle (Austenite Conditioning + Transformation Cooling + Precipitation Aging) to achieve conditions like TH1050 and RH950, or extreme cold reduction to achieve the ultra-high-strength Condition CH900.
| Material Classification | Semi-Austenitic Precipitation-Hardening Stainless Steel |
|---|---|
| UNS Designation | S17700 (Type 631) |
| Microstructure | Semi-Austenitic (Transforms to Martensitic upon conditioning) |
| Magnetic State | Weakly Magnetic (Condition A) | Strongly Magnetic (Hardened) |
| Density | ~7.80 g/cm³ (0.282 lb/in³) in Condition A |
| Size Range | Metric: M4 to M64 | Imperial: #8 to 2-1/2" Specializing in stamped washers, rings, and custom machined bolts. |
| Thread Types | UNC, UNF, 8UN, Metric Coarse, Metric Fine |
| Strengthening Method | Austenite Conditioning + Cryogenic Cooling + Precipitation Aging |
■ Proprietary Datasheet Download (GATED)
Access professional-grade technical data for 17-7 PH, including detailed austenite conditioning cycle charts, cryogenic transformation hold times, and fatigue-life testing for spring and washer applications.
17-7 PH (S17700) — Complete Technical Datasheet
Contains explicit heat treatment recipes for Conditions TH1050, RH950, and CH900, elevated temperature stress-relaxation data, and AMS 5644 specification compliance documentation.
⬇ DOWNLOAD DATASHEET■ MTC Integration Section
Because the mechanical integrity of 17-7 PH depends entirely on successful phase transformation, strict metallurgical documentation is non-negotiable.
- EN 10204 Type 3.1: Detailed reporting of actual ladle chemical analysis (highlighting exact Aluminum levels), final mechanical testing, and verification of multi-stage heat treatment execution.
- EN 10204 Type 3.2: Third-party witness certification facilitated for aerospace, nuclear, and critical defense supply chains.
■ Chemical Composition (UNS S17700)
Unlike 17-4 and 15-5 which use Copper, 17-7 relies on precisely controlled Aluminum additions to drive the precipitation-hardening reaction, while higher Chromium and Nickel levels provide the austenitic base structure.
| Chromium (Cr) | Nickel (Ni) | Aluminum (Al) | Carbon (C) | Manganese (Mn) | Silicon (Si) |
|---|---|---|---|---|---|
| 16.0 – 18.0 | 6.50 – 7.75 | 0.75 – 1.50 | 0.09 Max | 1.00 Max | 1.00 Max |
*Phosphorus (0.040 Max) and Sulfur (0.030 Max) are tightly controlled. Notice the absence of Copper and Columbium compared to other PH grades.
■ Mechanical Properties (By Heat Treatment Condition)
17-7 PH can achieve incredibly high ultimate tensile strengths, particularly in Condition CH900 (which requires severe cold-working prior to aging), making it one of the strongest stainless alloys available.
| Property | Condition TH1050 | Condition RH950 | Condition CH900 (Max Strength) |
|---|---|---|---|
| Tensile Strength (Min) | 170 ksi (1170 MPa) | 210 ksi (1450 MPa) | 240 ksi (1655 MPa) |
| Yield Strength (0.2% Offset, Min) | 140 ksi (965 MPa) | 190 ksi (1310 MPa) | 230 ksi (1585 MPa) |
| Elongation in 2" (Min) | 6% | 4% | 1% to 2% |
| Hardness (Rockwell C) | 38 HRC Min | 46 HRC Min | 49 HRC Min |
■ Equivalent Grades & Designations
| Standard / System | Designation |
|---|---|
| UNS Designation | S17700 |
| Common Trade Name | 17-7 PH, Type 631 Stainless |
| European Equivalent | EN 1.4568 / X7CrNiAl17-7 |
| ASTM Specifications | ASTM A564 Grade 631 |
| Aerospace Specs | AMS 5644, AMS 5528, AMS 5529 |
■ Applications & Industries
Due to its high fatigue life, excellent formability before aging, and extreme post-aging strength, 17-7 PH is extensively used in applications requiring spring-like properties and corrosion resistance.
- Aerospace & Aviation: Belleville washers, high-strength retaining rings, precision springs, and aircraft skin fasteners.
- Petrochemical & Processing: High-stress burst discs, pressure relief valve components, and specialized structural brackets.
- Medical Devices: Surgical instrumentation and high-strength orthopedic components.
- Industrial Automation: Flexures, strain gauge bodies, and high-cycle dynamic loading components.
■ Compatible Fastener Assemblies
17-7 PH is highly susceptible to thread galling due to its hardness and stainless composition. Proper mating material selection is critical.
| External Threads (17-7 PH Studs/Bolts) | Recommended Mating Component (Nuts) |
|---|---|
| 17-7 PH Any Condition | 17-7 PH Heavy Hex Nuts (Extreme anti-seize lubrication required) |
| 17-7 PH Any Condition | Nitronic 60 (UNS S21800) Nuts (Superior galling prevention without liquid lube) |
■ Torque & Installation Guidelines
Given the immense yield strength of 17-7 PH (especially in RH950 and CH900), it can sustain massive torque loads. However, to prevent shear failure or cold-welding, Molybdenum Disulfide (MoS2) or heavy Nickel anti-seize must be applied to all active threads.
| Nominal Diameter | Threads Per Inch (UNC) | Target Torque (TH1050) — Lubricated (ft-lbs) |
|---|---|---|
| 3/8" | 16 | 35 - 45 |
| 1/2" | 13 | 75 - 90 |
| 5/8" | 11 | 145 - 170 |
| 3/4" | 10 | 260 - 300 |
■ Why Choose Ananka Group?
Ananka Group masters the complex metallurgy required to transform 17-7 PH from a soft, workable alloy into a high-strength industrial component.
- Expert Multi-Stage Thermal Processing: We execute the precise multi-step processes (Conditioning, Cryo-Cooling at -100°F, and final Aging) required for RH950 in-house.
- Precision Stamping & Machining: Expertise in cold-working and stamping Condition C material before aging it to the ultra-hard CH900 state for custom washers and springs.
- Advanced Traceability: 100% heat lot tracking mapping all thermal stages directly back to the original steel mill.
- Custom Surface Coatings: Dry-film lubricants (PTFE, Xylan) available to mitigate galling in high-torque installations.
■ Frequently Asked Questions
1. What does "Semi-Austenitic" mean?
It means the alloy is austenitic when purchased in its standard annealed condition (Condition A), making it relatively soft, easily formable, and weakly magnetic—similar to 304 stainless. However, through specific heat treatments, its internal structure transforms to martensite, allowing it to be hardened to extreme strength levels.
2. What is the difference between 17-7 PH and 17-4 PH?
17-4 PH is strictly martensitic (hard and less formable in all states) and uses Copper for hardening. 17-7 PH is semi-austenitic (highly formable before treatment), uses Aluminum for hardening, and can reach higher ultimate tensile strengths, making it the preferred choice for springs and flat components.
3. What is Condition CH900?
CH900 is achieved by taking Condition C material (which has already been severely cold-rolled/cold-worked at the mill to transform it to martensite) and aging it at 900°F. This results in the highest possible strength (up to 240 ksi) but very low ductility, ideal for springs and retaining rings.
4. Does 17-7 PH lose strength at high temperatures?
17-7 PH maintains exceptional mechanical properties and resists stress-relaxation at elevated temperatures up to approximately 600°F (316°C). Prolonged exposure above this threshold can cause over-aging and a reduction in strength.