There is a material that achieves a rare balance between mechanical strength and corrosion resistance — 17-4 PH stainless steel. This precipitation-hardened martensitic stainless steel alloy, officially designated UNS S17400, is widely used in demanding industries such as aerospace, medical devices, food processing, and even nuclear reactors. It has become an indispensable solution recommended by engineers across many fields.
What is 17-4 PH Stainless Steel?
17-4 PH stainless steel is a martensitic stainless steel alloy strengthened by precipitation hardening. It is a variant of the 17-4 alloy, typically heat treated to reach the strength and hardness required by engineers. Due to its versatile properties, it is one of the most widely used stainless steels today.
Differences Between 17-4 PH and 17-4 Stainless Steel
These two materials are often confused. While they have similar composition and performance, 17-4 PH stainless steel undergoes precipitation hardening heat treatment, whereas 17-4 stainless steel is a more general martensitic PH stainless steel that transforms into a martensitic crystal structure at high temperature.
The main difference lies in the increased niobium (Nb) content in 17-4 PH, which improves strength. This additional processing and material content make 17-4 PH more expensive but better suited for demanding applications.
Key Material Properties of 17-4 PH Stainless Steel
One of the notable features of 17-4 PH is its ability to achieve very high tensile strength after heat treatment without sacrificing corrosion resistance, thanks to its unique combination of chromium, nickel, and copper.
| Property | Annealed (Condition A) | H900 (Peak Hardness) | H1150 (Improved Toughness) |
|---|---|---|---|
| Tensile Strength (MPa) | ~850 | ~1310 | ~1100 |
| Yield Strength (MPa) | ~585 | ~1170 | ~1035 |
| Elongation (%) | 24 | 10 | 12 |
| Hardness (HRC) | 25 | 44 | 38 |
| Corrosion Resistance | Moderate | Moderate | Moderate |
Unlike austenitic stainless steels like 304 or 316, 17-4 PH hardens through heat treatment instead of cold working. After solution annealing, it undergoes aging (such as H900, H1025, or H1150), precipitating copper phases to strengthen the martensitic structure.
For maximum strength, the H900 condition is preferred, while for improved toughness under impact, H1025 or H1150 are commonly chosen.
Applications of 17-4 PH Stainless Steel
Aerospace components: turbine engine parts, fasteners, structural brackets
Medical instruments: surgical tools, orthopedic screws, dental hardware
Defense systems: missile parts, firearms components, underwater weapons
Food processing: shafts, valves, mixer blades — benefiting from corrosion resistance
Energy sector: nuclear reactor components, high-pressure seals, pump shafts
These applications require a stainless steel that remains stable under thermal cycling, resists chloride-induced corrosion, and withstands mechanical loads without deformation.
Six Key Dimensions of 17-4 PH Stainless Steel
Mechanical Properties
Dependent on aging condition. In H900 (480°C aging), tensile strength reaches 1310–1450 MPa, yield strength 1170–1240 MPa, hardness HRC 40–44, with elongation around 10–12%.
In H1150 (620°C aging), strength decreases to 930–1070 MPa, elongation increases to 14–16%, hardness drops to HRC 28–33.
This adjustable strength-to-ductility balance is a core advantage over 304/316 stainless steels, which only reach 500–700 MPa. Fatigue strength in H900 can reach ±600 MPa (10⁷ cycles), suitable for high-cycle fatigue applications.
Physical Properties
Density is about 7.80 g/cm³, similar to conventional austenitic stainless steels. Magnetic properties depend on structure: solution annealed (Condition A) is weakly magnetic, while aged martensitic form is strongly magnetic (relative permeability μᵣ >100).
Electrical resistivity is around 0.80 μΩ·m, slightly higher than 304 (0.72 μΩ·m), requiring higher welding currents. Elastic modulus is 196 GPa, and thermal expansion between 20–100°C is 10.8×10⁻⁶/K, lower than 304 stainless steel’s 17.3×10⁻⁶/K — important for thermal matching designs.
Thermal Properties
Melting point ranges from 1400 to 1440°C. Thermal conductivity is about 18.4 W/(m·K), slightly lower than 304 stainless steel (16.2 W/(m·K)), which can cause heat buildup during machining and necessitates effective cooling.
High-temperature strength is excellent: at 300°C, H900 maintains over 800 MPa tensile strength — about three times that of 304 stainless steel.
Maximum continuous service temperature is 300°C; beyond this, copper-rich precipitates coarsen and degrade strength. At 600°C, strength falls to 40% of room temperature value.
Corrosion Resistance
Corrosion resistance varies with aging condition. H1150 performs close to 304 stainless steel in mild environments (air, fresh water) but weaker in chloride environments: critical pitting temperature in 3% NaCl is only 10°C, lower than 316’s 25°C.
Stress corrosion cracking resistance surpasses 304, especially in H1150. H900 has 20–30% lower corrosion resistance due to grain boundary precipitates. Acidic environments (pH < 4) recommend surface passivation (e.g., nitric + chromic acid) to improve passive film stability.
Heat Treatment Process
Heat treatment activates 17-4 PH’s performance through solution annealing plus aging.
Solution annealing at 1040±15°C for 0.5–1 hour, followed by water quenching (oil quenching causes carbide precipitation), yielding supersaturated martensite (HRC ~32).
Aging treatments: 480°C×1–4h (H900) for max strength; 565°C×4h (H1075) for balanced toughness; 620°C×4h (H1150) for corrosion resistance optimization.
Precise aging temperature control (±5°C) is crucial; 10°C deviation at 480°C can cause ±15% strength fluctuation. Complex parts may require 620°C×2h stress relief annealing before aging to prevent distortion and cracking.
Weldability
Weldable by TIG, EBW, and other methods with strict controls. Use matching filler metals (e.g., ER630, ≤0.6% Si) and limit heat input to ≤1.0 kJ/mm (TIG).
Post-weld heat treatment (PWHT) is mandatory: full solution anneal at 1040°C plus re-aging, except EBW which has ultra-low heat input.
Skipping solution anneal reduces heat-affected zone strength by over 50%. For parts that cannot undergo full heat treatment, local aging at 620°C×4h is recommended but strength only recovers to solution-annealed level.
Machining 17-4 PH Stainless Steel
CNC Milling
Ideal for complex 3D profiles. Use multi-flute carbide tools with roughing depths up to 50% of tool diameter and 0.1 mm finishing allowance. High-pressure internal cooling (≥70 bar) with chlorine-free synthetic coolant keeps temperature under 250°C and prevents built-up edge.
Achievable tolerance ±0.025 mm, suitable for aerospace structural parts and hydraulic valves.
CNC Turning
Efficient for shafts and discs. Use CCGT inserts, spindle speeds 150–220 m/min, feed rates 0.08–0.15 mm/rev. For hardened states, CBN inserts improve surface finish. Use tailstock support for thin walls; chip breakers to avoid long chips. Turning mainly done in solution annealed condition, with minor grinding allowed after aging.
Drilling
Use cobalt carbide drills with 135° tip and peck drilling every twice drill diameter. Key points: pre-center drilling to prevent runout, internal cooling with extreme pressure additives, speed 20–35 m/min, feed 0.03 mm/rev to avoid work hardening. For holes deeper than 5× diameter, use parabolic flute drills and finish with reamers to achieve Ra 0.8 μm surface.
EDM
Electrical discharge machining uses spark erosion, ideal for narrow slots and micro-features. Employ brass or graphite electrodes in kerosene dielectric. Rough cuts use long pulses; finishing uses short pulses for Ra 0.2 μm surface. Post-EDM sandblasting removes recast layer (~0.03 mm), followed by low-temperature aging (620°C×4h) to restore properties.
Wire EDM
Uses 0.2 mm molybdenum wire in deionized water; suitable for hardened parts.
Laser Cutting
4 kW fiber laser with nitrogen assist can cut up to 12 mm thick plates. Thermal affected zone requires post-processing machining.
Grinding
After aging, use ceramic-bonded CBN wheels at 35 m/s with light passes (0.005 mm/pass) for dimensional stability.
Why Choose JeekRapid for Your 17-4 PH Stainless Steel CNC Machining?
JeekRapid offers reliable one-stop CNC machining services for 17-4 PH stainless steel parts. Our team of experienced engineers, machinists, and quality specialists work closely to ensure your products meet stringent standards.
We utilize advanced CNC technologies, including 3-axis, 4-axis, and 5-axis milling, turning, EDM, and finishing processes to deliver precise, high-quality stainless steel parts. Besides 17-4 PH, we machine 304, 316, and other alloys, providing flexibility to meet your specific project requirements.
Get a free quote today and start your project with JeekRapid.
Frequently Asked Questions (FAQ)
Q1: What is the typical delivery time for machining 17-4 PH stainless steel parts?
A: Delivery times depend on part complexity and order volume. Generally, standard low to medium volume orders are shipped within 5 to 15 business days.
Q2: Does JeekRapid handle both prototype and production runs?
A: Yes, we specialize in CNC machining for both prototypes and production, capable of handling quantities from one piece up to thousands.
Q3: Which heat treatment conditions of 17-4 PH stainless steel do you machine?
A: We machine all common conditions, including annealed (Condition A) and hardened states such as H900, H1025, and H1150.
Q4: Do you provide material sourcing as part of your service?
A: Yes, we can source certified 17-4 PH stainless steel materials or use customer-supplied stock.
