17-4PH vs 17-7PH Precipitation Hardening
Date: 2026年9月14日 Categories: News Views: 325
By Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier | ISO 9001:2015 | Est. 2012
Contact: sales@hangboalloy.com | hangbo@nickel-alloy.com | WhatsApp (Lisa): +86 13611656360
Quick Answer: What Is the Difference Between 17-4PH and 17-7PH?
17-4PH (UNS S17400) and 17-7PH (UNS S17700) are both precipitation-hardening stainless steels with ~17% chromium, but they harden by different mechanisms and serve different purposes. 17-4PH is martensitic — it contains 4% copper and hardens through a copper-rich precipitate, reaching very high strength (up to ~1310 MPa) with good corrosion resistance; it is used for shafts, valves, and structural parts. 17-7PH is semi-austenitic — it contains aluminum and hardens through a nickel-aluminide precipitate, offering superior formability in the annealed state plus excellent spring properties; it is the classic choice for springs, diaphragms, and bellows.
Composition Comparison (wt.%)
| Element | 17-4PH (S17400) | 17-7PH (S17700) |
|---|---|---|
| Chromium | 15.5-17.5 | 16-18 |
| Nickel | 3.0-5.0 | 6.50-7.75 |
| Copper | 3.0-5.0 | -- |
| Aluminum | -- | 0.75-1.50 |
| Carbon | 0.07 max | 0.09 max |
| Structure | Martensitic | Semi-austenitic |
Mechanical Properties Comparison (Peak Aged)
| Property | 17-4PH (H900) | 17-7PH (CH900) |
|---|---|---|
| Tensile Strength | 1310 MPa | 1650 MPa |
| Yield Strength | 1170 MPa | 1380 MPa |
| Elongation | 10-16% | 6-10% |
| Hardness | 40-47 HRC | 44-50 HRC |
| Spring properties | Moderate | Excellent |
Corrosion & Processing Comparison
| Property | 17-4PH | 17-7PH |
|---|---|---|
| Corrosion resistance | Good | Good |
| Formability (annealed) | Limited | Excellent |
| Machinability | Better | Moderate |
| Weldability | Good | Good |
| Max service temperature | ~300C | ~315C |
| Spring/diaphragm use | Moderate | Excellent |
Which One for Your Application?
| Application | Best Choice | Why |
|---|---|---|
| Pump shafts | 17-4PH | Strength + machinability |
| Valve stems/balls | 17-4PH | Wear + corrosion |
| Aerospace structural | 17-4PH | High strength |
| Springs (flat/coil) | 17-7PH | Best spring properties |
| Diaphragms | 17-7PH | Formability + fatigue |
| Bellows | 17-7PH | Thin-section forming |
Price Comparison (2026, EXW)
| Form | 17-4PH | 17-7PH |
|---|---|---|
| Round Bar | \$8-14/kg | \$12-20/kg |
| Plate | \$9-15/kg | \$13-21/kg |
| Strip/Coil | \$10-17/kg | \$14-23/kg |
17-7PH is typically 40-50% more expensive due to higher nickel and tighter processing.
FAQ
Q1: Is 17-7PH stronger than 17-4PH?
In peak-aged condition yes (up to ~1650 MPa vs ~1310 MPa), but 17-7PH is primarily used for springs.
Q2: What are the UNS numbers?
S17400 = 17-4PH; S17700 = 17-7PH.
Q3: Which is easier to machine?
17-4PH — 17-7PH's retained austenite makes it gummy.
Q4: Which is better for springs?
17-7PH, thanks to its formability and fatigue resistance.
Q5: Can 17-4PH be used in seawater?
Limited — it is susceptible to pitting; consider 17-4PH H1150 or a nickel alloy for marine service.
Q6: What heat treatments apply?
17-4PH: 1040C solution + 480-620C age. 17-7PH: 1065C austenitize + conditioning + 510-565C age.
Q7: What does Shanghai Hangbo supply?
Both grades in bars, plates, strips, and wire with EN 10204 3.1 certification. SGS/TUV/BV available.
Contact & Complete Product Range
Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier
Email: sales@hangboalloy.com | WhatsApp (Lisa): +86 13611656360 | www.nickel-alloy.com
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