17-4PH stainless steel is the grade engineers choose when a component must combine high strength, good corrosion resistance, and the ability to be heat-treated to precise mechanical properties. Known internationally as UNS S17400 and AISI 630, this precipitation-hardening martensitic stainless steel can be aged from a relatively soft Condition A state to a peak-strength H900 condition with tensile strength above 1,310 MPa.
That hardness range, roughly 28 HRC in H1150 up to 47 HRC in H900, is not a manufacturing defect. It is the entire reason the alloy exists. Pick the wrong condition and a valve stem may be too brittle, a pump shaft may gall prematurely, or a machined aerospace fitting may distort during aging. Pick the right condition and 17-4PH delivers a strength-to-weight ratio that rivals many nickel alloys at a lower cost.
This guide explains 17-4PH stainless steel composition, mechanical properties, heat treatment conditions, hardness values, corrosion behavior, machining and welding considerations, and how to source certified material from China. Whether you are writing a specification, reviewing a mill test report, or comparing grades for a new design, the information below will help you make the right engineering decision.
Key Takeaways
- 17-4PH stainless steel (UNS S17400 / AISI 630) is a precipitation-hardening martensitic grade with 17% chromium and 4% nickel.
- Hardness ranges from ~28 HRC in H1150 to ~47 HRC in H900, controlled entirely by aging temperature.
- The Chinese equivalent is 0Cr17Ni4Cu4Nb / SUS630 per GB/T 1220, with matching mechanical properties.
- H1150D is commonly specified for NACE MR0175 sour service because it keeps hardness below ~33 HRC.
- Machine in Condition A (solution annealed) and age afterward; aged H900 is abrasive and work-hardens rapidly.
- Weld with matching ER630 filler metal and apply post-weld heat treatment to restore strength and corrosion resistance.
- Zhonggongte supplies 17-4PH bar, plate, sheet, pipe, tube, wire, and forgings with ASTM/AMS certification and full MTR documentation.
What Is 17-4PH Stainless Steel?
17-4PH stainless steel is a precipitation-hardening martensitic stainless steel (UNS S17400 / AISI 630) containing approximately 17% chromium and 4% nickel. It is strengthened by aging heat treatment, giving hardness from 24 HRC (H1150D) to 47 HRC (H900) and tensile strength above 1,310 MPa. It is used in aerospace, oil and gas, marine, and chemical processing components.
Grade Designations and Naming
17-4PH belongs to the precipitation hardening stainless steel family, a group of martensitic stainless steel grades that are strengthened by copper-rich precipitates during aging. The name describes the approximate composition: about 17% chromium and 4% nickel, with the “PH” indicating that copper-rich precipitates form during aging to strengthen the martensitic matrix.
| System | Designation |
|---|---|
| UNS | S17400 |
| AISI / ASTM | Type 630 |
| EN | 1.4542 / X5CrNiCuNb16-4 |
| JIS | SUS630 |
| Chinese GB/T | 0Cr17Ni4Cu4Nb |
For buyers sourcing from Chinese mills, the 17-4PH stainless steel equivalent is 0Cr17Ni4Cu4Nb (GB/T) or SUS630 (JIS). These are the direct metallurgical equivalents of 17-4PH. They follow the same chemical composition limits, respond to the same heat treatment cycles, and deliver the same hardness ranges when produced to GB/T 1220 or export standards such as ASTM A564 and AMS 5643.
Microstructure and Magnetic Behavior
Unlike austenitic grades such as 304 stainless steel or 316L, 17-4PH has a martensitic microstructure. This makes it magnetic in all heat treatment conditions, a useful property for some sensor and actuator applications, but a limitation for MRI equipment or non-magnetic assemblies.
The alloy transforms to martensite on cooling from the solution-annealing temperature. Subsequent aging precipitates fine copper and niobium carbide phases that pin dislocations and raise hardness. The result is a material that can be tuned from tough and ductile (H1150) to extremely strong and wear-resistant (H900).
17-4PH Stainless Steel Chemical Composition
ASTM A564 and ASTM A693 define the composition limits shown below. These ranges ensure that the alloy responds predictably to solution annealing and aging.
| Element | ASTM A564 / A693 Limit (wt%) | Role |
|---|---|---|
| Carbon (C) | ≤ 0.07 | Keeps martensite soft enough to age without excessive brittleness |
| Chromium (Cr) | 15.0 – 17.5 | Provides stainless characteristics and moderate corrosion resistance |
| Nickel (Ni) | 3.0 – 5.0 | Stabilizes austenite during solution treatment, improves toughness |
| Copper (Cu) | 3.0 – 5.0 | Primary precipitation-hardening element |
| Niobium + Tantalum (Nb + Ta) | 0.15 – 0.45 | Forms carbides and refines grain structure |
| Manganese (Mn) | ≤ 1.00 | Deoxidizer, improves hot workability |
| Silicon (Si) | ≤ 1.00 | Deoxidizer |
| Phosphorus (P) | ≤ 0.040 | Controlled impurity |
| Sulfur (S) | ≤ 0.030 | Controlled impurity |
| Iron (Fe) | Balance | Matrix element |
The combination of copper and niobium is what distinguishes 17-4PH from standard martensitic grades such as 410 or 431. Without copper, the alloy could not precipitation-harden to the strength levels that make 17-4PH valuable for aerospace and oil and gas components.
In addition to the elements above, 17-4PH density is approximately 7.78 g/cm³, and its coefficient of thermal expansion is roughly 10.8 × 10⁻⁶ /°C between 20°C and 100°C.
17-4PH Stainless Steel Mechanical Properties by Condition
17-4PH properties are controlled mainly by aging temperature. The grade is almost always supplied in the solution-annealed Condition A and then aged by the user or supplier to the desired H-condition. The aging temperature controls the final strength, hardness, and toughness.
| Condition | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Hardness (HRC) |
|---|---|---|---|---|
| A (solution annealed) | ≥ 930 | ≥ 725 | ≥ 16 | ~28–32 |
| H900 | ≥ 1,310 | ≥ 1,170 | ≥ 10 | 40–47 |
| H1025 | ≥ 1,070 | ≥ 1,000 | ≥ 12 | 35–42 |
| H1075 | ≥ 1,000 | ≥ 860 | ≥ 13 | 31–38 |
| H1100 | ≥ 965 | ≥ 795 | ≥ 14 | 28–37 |
| H1150 | ≥ 930 | ≥ 725 | ≥ 16 | 28–37 |
| H1150D | ≥ 860 | ≥ 655 | ≥ 18 | 24–33 |
Values shown are typical specification minima or common ranges. 17-4PH yield strength and 17-4PH tensile strength both increase as the aging temperature decreases, while ductility moves in the opposite direction. Actual properties vary with product form, section size, and exact heat treatment practice. For design-critical applications, always specify the relevant standard and confirm the minimum values for your product form.
When Acme Aerospace needed landing gear pins with both high fatigue strength and enough toughness to survive impact loading, their materials team specified H1025 rather than H900. The slightly lower hardness gave them a better strength-to-toughness balance, and the pins passed qualification testing without the brittleness risk associated with peak-aged H900.
17-4PH Stainless Steel Hardness Chart by Heat Treatment Condition
The 17-4PH hardness chart below shows that hardness is not a single number, it is a direct result of the aging temperature selected after solution annealing.
| Condition | Aging Temperature | Typical HRC | Typical HB |
|---|---|---|---|
| H900 | 482°C / 900°F | 40–47 | 388–444 |
| H1025 | 552°C / 1,025°F | 35–42 | 331–401 |
| H1075 | 580°C / 1,075°F | 31–38 | 302–375 |
| H1100 | 593°C / 1,100°F | 28–37 | 293–363 |
| H1150 | 621°C / 1,150°F | 28–37 | 277–352 |
| H1150D | Double 621°C | 24–33 | 255–311 |
Lower aging temperatures produce finer copper precipitates and higher hardness. Higher aging temperatures coarsen the precipitates, reducing hardness but improving toughness, ductility, and stress-corrosion resistance. This trade-off is the central design decision when specifying 17-4PH.
For applications requiring maximum wear resistance and strength, such as high-performance fasteners, valve internals, or precision shafts, H900 is the usual choice. For applications where toughness, machinability, or corrosion resistance matters more, H1150 or H1150D is preferred.
17-4PH Stainless Steel Heat Treatment Conditions Explained
The 17-4PH heat treatment process has two stages: solution annealing followed by aging at a temperature that sets the final mechanical properties.
Condition A, Solution Annealed
Solution annealing is performed at approximately 1,020–1,060°C followed by air cool or oil quench. This step dissolves copper and carbides into a homogeneous austenite, which then transforms to soft martensite on cooling. Condition A is the starting point for all subsequent aging and is the best condition for machining and forming.
H900, Maximum Strength
Aging at 482°C (900°F) for approximately one hour produces the highest 17-4PH H900 hardness and tensile strength. H900 is used where wear resistance and static strength are the dominant requirements. The trade-off is lower toughness and reduced corrosion resistance compared to overaged conditions.
H1025 / H1075, Balanced Properties
These intermediate aging temperatures provide a compromise between strength and toughness. H1025 and H1075 are common choices for aerospace structural components, shafts, and fasteners where fatigue life and impact resistance matter.
H1150 / H1150D, Maximum Toughness and Corrosion Resistance
Aging at 621°C (1,150°F) gives the softest, toughest 17-4PH H1150 properties. H1150D involves a double aging cycle and is frequently specified for NACE MR0175 / ISO 15156 sour service applications because it limits hardness to approximately 33 HRC or below. The lower hardness also improves machinability and resistance to stress-corrosion cracking.
H1150M, Modified Overaging
H1150M uses an initial conditioning treatment near 760°C before final aging at 621°C. This modified cycle is designed to further improve toughness and stress-corrosion resistance in critical oil and gas components.
How to Heat Treat 17-4PH Stainless Steel
- Solution anneal at 1,020–1,060°C, then air cool or oil quench to Condition A.
- Select aging temperature based on required hardness: H900 (482°C), H1025 (552°C), H1075 (580°C), H1100 (593°C), H1150 (621°C), or H1150D (double 621°C).
- Age for the specified time, then cool to room temperature.
- Verify hardness and mechanical properties against the ordered standard.
For a deeper look at each cycle and when to choose each condition, see our dedicated 17-4PH heat treatment guide.
17-4PH Stainless Steel Corrosion Resistance
17-4PH offers good general corrosion resistance, roughly comparable to 304 stainless steel in mild atmospheric, fresh water, and many chemical environments. However, it is not a substitute for 316L stainless steel or duplex stainless steel in chloride-rich or marine immersion service. See our 17-4PH vs 316 comparison for a side-by-side grade review.
Key corrosion considerations:
- Chloride environments: Pitting and crevice corrosion resistance is lower than 316L because 17-4PH contains no molybdenum.
- Heat treatment effect: H1150 and H1150D generally show better corrosion resistance and stress-corrosion cracking resistance than H900.
- Passivation: A nitric acid passivation treatment after machining can improve corrosion performance in mild environments.
- Galvanic coupling: As a martensitic stainless steel, 17-4PH can create galvanic couples with more noble alloys; isolation may be needed in mixed-metal assemblies.
When a chemical processor in Southeast Asia replaced 304 valve stems with 17-4PH H1075, the higher strength allowed a smaller stem diameter and reduced actuator load. However, the plant later discovered that stagnant chloride process water caused localized pitting in the H900 trim of an adjacent valve. Switching the trim to H1150D and adding a passivation step solved the issue without sacrificing mechanical performance.
17-4PH Stainless Steel Applications and Uses
The combination of high strength, moderate corrosion resistance, and heat-treatable hardness makes 17-4PH suitable for a wide range of demanding applications.
Aerospace and Defense
- Aircraft structural fittings and fasteners
- Landing gear components
- Turbine and jet engine hardware
- Actuator assemblies and control surfaces
- Missile and ordnance components
Oil and Gas
- Valve stems, bodies, and trim
- Pump shafts and impellers
- Downhole tools and wellhead components
- Offshore platform fasteners
- Sour service components in H1150D condition
Marine
- Propeller shafts and couplings
- Underwater fasteners and fittings
- Boat hardware requiring high strength
- Ocean instrumentation housings
Chemical and Food Processing
- Reactor parts and pressure vessels
- Mixing shafts and agitators
- Food processing machinery
- Medical instruments and surgical tools
Industrial Manufacturing
- High-strength fasteners, gears, and couplings
- Molds, dies, jigs, and fixtures
- Wear-resistant bushings and precision hardware
- Robotics structural frames and joints
17-4PH is also supplied as stainless steel sheet and plate for tooling, fixtures, and structural panels that require high strength after heat treatment.
The grade is particularly valuable where a component must be machined to tight tolerances and then hardened to final strength, a combination that austenitic stainless steels cannot provide because they cannot be strengthened by heat treatment.
17-4PH Stainless Steel vs Other Stainless Steels
17-4PH vs 316 Stainless Steel
In the 17-4PH vs 316 stainless steel comparison, 316 stainless steel is an austenitic grade with 2–3% molybdenum, giving it superior chloride corrosion resistance and excellent weldability. However, 316 cannot be hardened by heat treatment; its yield strength in the annealed condition is only ~205–240 MPa. In contrast, 17-4PH H900 delivers yield strength above 1,170 MPa, roughly five times higher.
Choose 316 when corrosion resistance, ductility, and weldability are the top priorities. Choose 17-4PH when strength, hardness, and wear resistance are critical and corrosion exposure is moderate. If you are still deciding between austenitic grades, see our 304 vs 316 stainless steel comparison, then weigh whether 17-4PH’s heat-treatable strength is needed.
For a side-by-side comparison, see our 17-4PH vs 316 stainless steel guide.
17-4PH vs 15-5PH
15-5PH (UNS S15500) is also a precipitation-hardening martensitic stainless steel with a similar strengthening mechanism. The main differences are:
- Toughness: 15-5PH generally offers better transverse toughness and more uniform properties because of its cleaner microstructure.
- Corrosion resistance: 15-5PH is often slightly better than 17-4PH in chloride environments.
- Availability: 17-4PH is more widely stocked and typically less expensive.
- Applications: 15-5PH is preferred for aerospace structural components and applications requiring high toughness in transverse directions; 17-4PH is the default choice for general high-strength components.
17-4PH vs 304 Stainless Steel
304 stainless steel is the most common austenitic grade. It is non-magnetic, easy to form and weld, and cost-effective. However, its yield strength is only ~215 MPa, and it cannot be heat-treated for higher strength. 17-4PH is magnetic, harder to form, and more expensive, but it delivers far higher strength and hardness after aging.
For applications such as high-strength fasteners, valve internals, or precision shafts, 17-4PH is the clear choice over 304. For general fabrication, food equipment, or architectural applications, 304 remains the standard.
17-4PH Stainless Steel Machining
17-4PH machinability is best in the Condition A (solution-annealed) state. Once aged, particularly to H900, the material becomes abrasive and work-hardens rapidly. The standard production strategy is therefore:
- Order bar or plate in Condition A.
- Machine to near-net shape using carbide tooling.
- Perform final aging to the required H-condition.
Recommended machining practice:
- Tooling: Use sharp, positive-rake carbide inserts coated with TiAlN or AlCrN. Cobalt HSS is acceptable for Condition A but wears quickly on aged material.
- Speeds and feeds: For Condition A turning with carbide, cutting speeds of 115–190 m/min are typical. Reduce speed by 20–30% for aged conditions.
- Depth of cut: Use aggressive depths and feeds to cut beneath the work-hardened layer. Light scratching cuts cause rapid tool wear.
- Coolant: Apply high-pressure coolant for heat removal and chip evacuation.
- Finishing: H900 precision features are often finished by grinding rather than cutting.
For detailed speeds, feeds, and tooling recommendations, see our 17-4PH machining guide.
17-4PH Stainless Steel Welding
A sound 17-4PH welding procedure uses GTAW (TIG), GMAW (MIG), or SMAW processes, with proper procedure control and post-weld heat treatment to restore properties and corrosion resistance. The principles are similar to those covered in our general stainless steel welding guide, though 17-4PH requires matching ER630 filler and post-weld aging.
Filler Metal Selection
| Application | Recommended Filler |
|---|---|
| Matching 17-4PH to 17-4PH | AWS A5.9 ER630 (UNS S17480) |
| Dissimilar welding to austenitic grades | 309L or 312L |
| Lower-strength, non-critical welds | 308L |
ER630 filler provides the closest match to the base metal in strength, hardness, and aging response. For welds that must match the base metal properties, ER630 is the correct choice.
Welding Procedure
- Preheat: Generally not required for sections under ~100 mm thickness.
- Interpass temperature: Keep below 150°C to avoid overheating and loss of properties.
- Shielding gas: Use 100% argon for GTAW with adequate gas coverage and back purging.
- Hydrogen control: Clean surfaces thoroughly and use low-hydrogen consumables to minimize cracking risk.
Post-Weld Heat Treatment
After welding, the component should be solution-annealed and re-aged to restore uniform properties throughout the weld metal and heat-affected zone. For some repairs, direct aging may be acceptable, but full re-solution and aging is preferred for critical applications.
For a full welding procedure discussion, see our 17-4PH welding guide.
17-4PH Stainless Steel Standards and Specifications
17-4PH is covered by several international standards. The most commonly referenced are:
| Standard | Scope |
|---|---|
| ASTM A564 | Hot-rolled and cold-finished age-hardening stainless steel bars and shapes |
| ASTM A693 | Precipitation-hardening stainless and heat-resisting steel plate, sheet, and strip |
| ASME SA693 | Boiler and pressure vessel code equivalent of ASTM A693 |
| AMS 5643 | Bars, forgings, and rings, corrosion and heat-resistant |
| AMS 5604 | Sheet, strip, and plate, corrosion and heat-resistant |
| AMS 5622 | Bars and forgings, premium aircraft quality |
For oil and gas sour service, NACE MR0175 / ISO 15156 places hardness limits on materials exposed to hydrogen sulfide environments. Depending on product form and clause, 17-4PH may qualify at hardness levels up to approximately 33 HRC when supplied in H1150D or similar overaged conditions. Always consult the latest NACE standard for your specific component and application.
For comparison, Inconel 718 is often specified for higher-temperature or more severely corrosive sour service conditions where 17-4PH reaches its limits. Our Inconel 718 complete technical guide covers that grade in detail. For additional property data, see the Sandmeyer 17-4PH technical datasheet.
Sourcing 17-4PH Stainless Steel from China
What to Specify in Your RFQ
A complete RFQ for 17-4PH stainless steel should include:
- Grade and standard: 17-4PH / UNS S17400 / AISI 630, or Chinese 0Cr17Ni4Cu4Nb / SUS630 per GB/T 1220
- Heat treatment condition: Condition A, H900, H1025, H1075, H1100, H1150, or H1150D
- Hardness requirement: Minimum, maximum, or target range
- Product form: stainless steel bar, plate, sheet, pipe, tube, wire, forging, or fastener
- Dimensions: Diameter, thickness, width, length, and tolerance
- Quantity: Weight or number of pieces
- Certification: MTR, EN 10204 3.1/3.2, third-party inspection, NACE compliance if required
- End use: Helps confirm condition selection and testing requirements
- Delivery terms: Incoterm, destination, and required delivery date
17-4PH stainless steel price depends on product form, condition, certification level, and order quantity. Requesting a complete RFQ with the details above helps suppliers quote accurately and reduces lead time.
What to Check on the MTR
Before accepting material, verify the material test report contains:
- Heat number and full chemical analysis
- Mechanical test results for the ordered condition
- Hardness value with test method and scale
- Heat treatment chart
- Melt practice statement
- EN 10204 3.1 or 3.2 certificate as required
- NDT reports if specified
When evaluating 17-4PH stainless steel suppliers, confirm that they can provide the ordered condition, heat treatment chart, hardness test method, and full MTR documentation.
Zhonggongte Capability
Jiangsu Zhonggongte Metallurgical Technology Co., Ltd. supplies 17-4PH stainless steel (UNS S17400 / AISI 630 / 0Cr17Ni4Cu4Nb) from Wuxi in bar, plate, sheet, pipe, tube, wire, and forged forms. Our in-house testing capability includes direct-reading spectrometry, tensile testing, and hardness testing by Rockwell, Brinell, and Vickers methods.
Every order ships with a material test report, and we can provide EN 10204 3.1/3.2 certification and third-party inspection on request. For customers with critical applications, we support witness testing and independent laboratory verification of hardness and mechanical properties.
Our metallurgical engineers review each RFQ to confirm that the proposed condition, hardness range, test method, and certification match the application. Submit your specification and we will respond within 24 hours with availability, pricing, and a clear certification pathway.
17-4PH Stainless Steel FAQ
What does PH stand for in 17-4PH?
PH stands for precipitation hardening. The alloy is strengthened by heat treatment that forms copper-rich precipitates in the martensitic matrix.
What is the hardness of 17-4PH stainless steel?
Typical hardness ranges from 28–32 HRC in Condition A, 40–47 HRC in H900, and 24–33 HRC in H1150D. The exact value depends on the aging temperature and time.
Is 17-4PH magnetic?
Yes. 17-4PH has a martensitic microstructure, so it is magnetic in all conditions.
Can 17-4PH be welded?
Yes, but welding usually requires post-weld solution treatment and aging to restore properties. ER630 filler metal is recommended for matching welds.
What is the difference between H900 and H1150?
H900 is aged at 482°C and gives maximum strength and hardness. H1150 is aged at 621°C and gives lower hardness but better toughness, ductility, and corrosion resistance.
How does 17-4PH compare to 316 stainless steel?
17-4PH is much stronger and harder than 316 but has lower corrosion resistance in chloride environments. 316 is non-magnetic, easier to weld, and better for aggressive chemical or marine service.
What is the Chinese equivalent of 17-4PH?
The Chinese equivalent is 0Cr17Ni4Cu4Nb or SUS630, covered by GB/T 1220. It has the same composition and heat treatment response as 17-4PH.
What is the maximum service temperature for 17-4PH?
For prolonged service, 17-4PH is generally limited to approximately 300°C (572°F). Above this temperature, over-aging reduces strength.
Can 17-4PH be used in sour service?
Yes, in the overaged H1150 or H1150D condition, 17-4PH can meet NACE MR0175 hardness requirements for sour (H₂S) service. Always confirm the specific NACE clause for your product form.
Conclusion
17-4PH stainless steel is a versatile, high-strength material whose value lies in its ability to be heat-treated to a precise balance of strength, hardness, and toughness. From the peak strength of H900 to the sour-service toughness of H1150D, the same alloy chemistry can be tailored to very different engineering requirements.
The key to specifying 17-4PH successfully is to match the heat treatment condition to the application. Order Condition A for machining, then age to final hardness. Choose H900 for maximum strength, H1025 or H1075 for balanced aerospace properties, and H1150D for NACE-compliant toughness and improved corrosion resistance.
Zhonggongte manufactures and supplies certified 17-4PH / UNS S17400 / 0Cr17Ni4Cu4Nb from Wuxi with in-house heat treatment, hardness testing, full material traceability, and export documentation. Whether your drawing calls for Condition A, H900, H1150D, or hardness-verified material, our team will confirm the certification pathway and deliver a quote within 24 hours.
