Stainless Steel, Precipitation Hardening
15-5PH Stainless Steel (S15500) Bar
A martensitic precipitation hardening chromium-nickel-copper stainless steel.
15-5 stainless steel is a martensitic precipitation-hardening stainless steel with approximately 15% chromium and 5% nickel. It has high strength, high hardness, and excellent corrosion resistance. Strength can be further increased by a single low temperature heat treatment. Compared to 17-4 , it offers better transverse toughness and ductility, better mechanical properties in larger cross-sections, and better forgeability.
It is readily weldable. It can be machined in any of the several thermal conditions available to this grade.
15-5 (AMS 5659) is used in a variety of industries including: Aerospace, chemical, food processing, general metal working, paper industries & petrochemical.
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S15500 Stainless Steel Related Specifications
| System / Standard | Country / Region | Grade / Designation |
| UNS | International | S15500 |
| Common name | International | 15-5PH |
| Trade name | International | XM-12 |
| EN / W.Nr. | Europe | 1.4545 / 1.4548 |
| EN Name | Europe | X5CrNiCu15-5 / X5CrNiCuNb15-5 |
| ASTM A564 | USA | UNS S15500 (XM-12, bars/forgings) |
| ASTM A693 | USA | UNS S15500 (XM-12, plate/sheet) |
| ASTM A705 | USA | UNS S15500 (XM-12, forgings) |
| AMS 5659 | USA / Aerospace | 15-5PH (bars, forgings, rings) |
| AMS 5862 | USA / Aerospace | 15-5PH (sheet, strip, plate) |
| AMS 5826 | USA / Aerospace | 15-5PH (wire) |
| GB (approx.) | China | 0Cr15Ni5Cu4Nb (15-5PH) |
| JIS (usage) | Japan | SUS 15-5PH |
Properties
Chemical Composition
15-5PH
| Chemical Element | % Present |
| Carbon (C) | 0.00 - 0.07 |
| Chromium (Cr) | 14.00 - 15.50 |
| Manganese (Mn) | 0.00 - 1.00 |
| Silicon (Si) | 0.00 - 1.00 |
| Phosphorous (P) | 0.00 - 0.03 |
| Sulphur (S) | 0.00 - 0.02 |
| Nickel (Ni) | 3.50 - 5.50 |
| Copper (Cu) | 2.50 - 4.50 |
| Molybdenum (Mo) | 0.00 - 0.50 |
| Niobium (Columbium) (Nb) | 0.00 - 0.45 |
| Iron (Fe) | Balance |
Mechanical Properties
15-5PH
| Mechanical Property | Value |
| Proof Stress | 700-1170 MPa |
| Tensile Strength | 930-1310 MPa |
| Elongation A50 mm | 10-16 % |
| Hardness Brinell | 277-444 HB |
General Physical Properties
Physical Properties of 15-5PH Stainless Steel
| Property | Metric | Imperial | Notes |
| Density | 7.75–7.80 g/cm³ | ≈ 0.28 lb/in³ | Similar to 17-4PH; used for weight calculations. |
| Modulus of Elasticity (E) | ≈ 200 GPa | ≈ 29 × 10⁶ psi | Longitudinal, room-temperature value. |
| Shear Modulus (G) | ≈ 77 GPa | ≈ 11.2 × 10⁶ psi | Derived from E and ν. |
| Poisson’s Ratio (ν) | ≈ 0.28 | ≈ 0.28 | Typical for martensitic PH stainless steels. |
| Coefficient of Thermal Expansion (20–100°C) | ≈ 10.8 × 10⁻⁶ /°C | ≈ 6.0 × 10⁻⁶ /°F | Similar order to 17-4PH / 13-8PH. |
| Thermal Conductivity | ≈ 18 W/m·K | ≈ 10.4 BTU/hr·ft·°F | At ~20°C. |
| Specific Heat Capacity | ≈ 460 J/kg·K | ≈ 0.11 BTU/lb·°F | Room-temperature value. |
| Electrical Resistivity | ≈ 0.98 μΩ·m | ≈ 38 μΩ·in | Increases somewhat with temperature. |
Applications of 15-5PH Stainless Steel
15-5PH stainless steel (UNS S15500, EN 1.4545, X5CrNiCuNb15-5) is a precipitation-hardening martensitic stainless steel that combines very high strength, good toughness (including transverse toughness) and useful corrosion resistance. It is widely used for high-integrity structural and mechanical parts, especially in aerospace and demanding industrial applications.
1. Aerospace Structural and Landing Gear Components
Highly stressed airframe fittings, brackets and structural members
Landing gear pins, axles, trunnions, cylinders and actuating components
Flight-control system parts, hinges and linkages requiring high strength-to-weight ratio
Hardware that needs good transverse properties and fracture toughness as well as corrosion resistance
2. High-Strength Shafts, Gears and Power-Transmission Parts
Rotor shafts, drive shafts and pump shafts in aerospace and industrial equipment
High-load gears, splined shafts and couplings operating under cyclic loading
Power-transmission components needing high fatigue strength and dimensional stability after aging
Precision rotating parts where both strength and corrosion resistance are required in compact designs
3. Fasteners, Fittings and Precision Hardware
High-strength bolts, screws, studs and nuts for aerospace, offshore and energy sectors
Pins, clevis pins, bushes and precision fittings in control and actuation systems
Connector bodies, adaptors and high-pressure fittings where leak-tightness and strength are critical
Hardware that must retain preload and resist relaxation in service
4. Valves, Pumps and Fluid-Control Components
Valve stems, seats, discs and internal trim for water, hydraulic fluids and process media
Pump shafts, impellers and wear rings in mildly to moderately corrosive environments
Flow-control components, chokes and regulators in aerospace, oil and gas and power-generation systems
Parts that combine pressure containment, wear resistance and corrosion resistance with high strength
5. Petrochemical, Offshore and Power-Generation Equipment
Components in petrochemical plants where high strength and corrosion resistance are both required
Hardware for offshore platforms and subsea equipment exposed to seawater spray or splash zones
High-stress parts in turbines, compressors and auxiliary power-generation equipment
Structural and rotating components where weight saving and reliability are important design drivers
6. Moulds, Tooling and Industrial Machinery
Injection-moulding machine parts such as tie bars, platens and high-strength tooling inserts
Corrosion-resistant tooling and fixtures exposed to cooling water, hydraulic fluids and shop environments
Precision mechanical parts in packaging, food-processing and industrial machinery that demand high strength and good surface finish
Wear-resistant components where 15-5PH can replace tool steels while offering better corrosion resistance
7. Medical, Instrumentation and High-Precision Components
High-strength, corrosion-resistant parts in medical devices and equipment (where the specific standard allows 15-5PH use)
Instrumentation housings, clamps and structural parts subjected to mechanical loading and corrosive atmospheres
Precision components that benefit from the alloy’s good machinability in the solution-treated state and dimensional stability after aging
Summary
15-5PH stainless steel is widely used for high-strength, high-reliability components such as aerospace structural and landing-gear parts, shafts and gears, fasteners and fittings, valve and pump internals, petrochemical and offshore hardware, tooling and precision mechanical components, wherever a combination of very high strength, good toughness (including transverse), dimensional stability after aging and useful corrosion resistance is required in demanding service environments.
Characteristics of 15-5PH Stainless Steel
15-5PH stainless steel (UNS S15500, EN 1.4545, X5CrNiCuNb15-5) is a precipitation-hardening martensitic stainless steel designed to provide very high strength, good toughness (including transverse toughness) and useful corrosion resistance, with improved property consistency compared to older PH grades like 17-4PH.
1. Precipitation-Hardening Martensitic Stainless Steel
15-5PH is a Cr–Ni–Cu–Nb (Cb) precipitation-hardening martensitic stainless steel.
Strength is developed by solution treatment + aging, which produces a martensitic matrix strengthened by fine copper-rich precipitates and carbides.
The alloy is supplied solution-treated and then aged to conditions such as H900, H1025, H1100, etc., to reach the specified strength and toughness.
2. High Strength and Hardness After Aging
15-5PH can achieve very high tensile and yield strength in the H900–H1025 conditions.
Strength levels are comparable to, or higher than, 17-4PH at similar aging temperatures.
By choosing different aging temperatures, designers can tune:
Yield and tensile strength
Hardness
Toughness and fatigue performance
This allows the same grade to be used for both ultra high-strength and more toughness-critical components.
3. Improved Toughness and Transverse Properties
A key advantage of 15-5PH over 17-4PH is its improved toughness and more uniform properties, especially in the transverse direction.
Cleaner steelmaking practices and controlled composition reduce segregation and non-metallic inclusions.
As a result, 15-5PH offers:
Better through-thickness and transverse toughness
More consistent mechanical properties across large sections and complex shapes
This makes it attractive for aerospace structural parts, landing gear and highly stressed fittings.
4. Good Corrosion Resistance
15-5PH offers corrosion resistance similar to 17-4PH and better than conventional martensitic stainless steels (e.g. 410 / 420).
It performs well in many atmospheric, fresh-water and mildly corrosive industrial environments.
While it does not match molybdenum-bearing austenitic grades (e.g. 316) in very aggressive chloride or chemical media, it provides an excellent balance of strength + corrosion resistance for many mechanical and structural applications.
5. Heat Treatment Flexibility and Dimensional Stability
Like other PH stainless steels, 15-5PH is heat treated by aging at relatively low temperatures after solution treatment.
This gives good dimensional stability, allowing tight tolerances to be achieved after final aging with minimal distortion.
Different aging conditions (e.g. H900, H1025, H1075, H1100) offer a spectrum from maximum strength to higher toughness and better stress-corrosion performance, letting engineers optimise properties for each design.
6. Machinability and Fabrication Behaviour
Machinability of 15-5PH is moderate to good for a high-strength stainless steel:
Rough machining is typically done in the solution-treated or softer aged conditions.
After aging, light finishing cuts and grinding achieve final dimensions and surface finish.
The alloy can also be forged and hot worked using standard high-alloy practices, then solution treated and aged.
With suitable procedures and fillers, 15-5PH is weldable, though—as with all high-strength martensitic PH grades—post-weld aging and careful heat-input control are important to maintain toughness and corrosion resistance.
7. Magnetic Properties
Because it is a martensitic precipitation-hardening stainless steel, 15-5PH is strongly magnetic in all aged conditions.
This is useful for applications involving magnetic clamping, sensing or assembly and distinguishes it from non-magnetic austenitic grades like 304 / 316 in the annealed state.
Summary
15-5PH stainless steel is a high-strength, precipitation-hardening martensitic alloy that combines very high tensile and yield strength, improved toughness and transverse properties, good corrosion resistance, heat-treatment flexibility, reasonable machinability and strong magnetism, making it a preferred choice for aerospace structural parts, landing-gear components, high-strength shafts, gears, fasteners, valve and pump internals, and other critical mechanical applications where reliability and property consistency are essential.
Additional Information
Weldability
Weldability of 15-5PH Stainless Steel
15-5PH stainless steel (UNS S15500, 1.4545) is weldable, but like all high-strength precipitation-hardening martensitic stainless steels it must be welded with controlled procedures and appropriate post-weld heat treatment to maintain strength, toughness and corrosion resistance.
1. General Weldability Characteristics
15-5PH can be welded by common fusion processes, but it is not as forgiving as austenitic grades such as 304/316.
The alloy should be treated as a high-strength, crack-sensitive material, especially in hardened conditions.
Incorrect procedures (no PWHT, excessive heat input, poor filler choice) can lead to:
Reduced toughness in the weld and HAZ
Local soft spots or over-hard regions
Increased risk of cracking and reduced corrosion resistance
2. Recommended Welding Condition of the Base Metal
Welding is normally done in the solution-treated (unaged) condition.
After welding, the whole part or assembly is aged to the specified condition (e.g. H900, H1025, H1100).
Welding in fully aged, maximum-strength conditions is not recommended except for very minor, non-critical operations, because:
The risk of cold cracking and loss of toughness is higher
Property control across the weld and HAZ is more difficult
3. Suitable Welding Processes
15-5PH can be welded with most standard processes, for example:
GTAW (TIG) – preferred for high-quality, low-heat-input welds and thin sections
GMAW (MIG) – suitable for production welding of thicker sections with good parameter control
SMAW (MMA) – usable for repair and site welding with low-hydrogen electrodes
Laser or electron-beam welding – for precision joints and minimal distortion in critical components
Process selection depends on thickness, joint design, accessibility and quality/inspection requirements.
4. Filler Metal Selection
For matching strength and corrosion behaviour, 15-5PH or 17-4PH-type matching fillers are typically used.
Matching fillers allow weld metal to respond to aging heat treatment in a similar way to the base metal, giving:
Comparable strength
Consistent hardness across weld, HAZ and parent material
In some special cases, austenitic stainless fillers may be used (e.g. for dissimilar joints or to maximise weld toughness), but:
Weld-metal strength will be lower than that of aged 15-5PH
This is usually acceptable only where the weld is not the critical load path
5. Preheat and Interpass Temperature Control
Preheat is generally modest or not required for thin or lightly restrained joints, but for thicker or highly restrained sections a moderate preheat can:
Reduce cooling rate
Lower the risk of hydrogen-assisted cracking
Interpass temperature should be controlled:
Avoid very low interpass temperatures that cause steep thermal gradients
Avoid excessive build-up of heat that can over-temper or coarsen the microstructure
In all cases, aim for consistent, moderate heat input rather than wide swings in temperature.
6. Post-Weld Heat Treatment and Aging
The usual route is:
Weld in the solution-treated state
Then age the entire component to the required condition (H900, H1025, H1100, etc.)
Benefits of post-weld aging:
Restores high strength in weld metal and HAZ
Helps equalise hardness and microstructure across the joint
Relieves a significant portion of residual stresses from welding
For the most critical components, specifications may call for:
Re-solution treatment followed by aging after welding, or
A specific combined PWHT cycle qualified by testing
7. Effect on Mechanical and Corrosion Properties
Properly welded and aged joints can achieve:
Strength levels close to the parent 15-5PH
Good toughness, including acceptable transverse toughness
Corrosion resistance similar to the base metal in the intended environment
Poor welding practice can lead to:
Soft, under-aged or over-aged regions with reduced strength
Brittle zones with low impact toughness
Reduced resistance to stress-corrosion cracking or general corrosion, especially near weld toes
Summary
15-5PH stainless steel is weldable, but must be handled as a high-strength precipitation-hardening martensitic alloy: weld in the solution-treated condition using controlled heat input and suitable matching fillers, then apply an appropriate aging or post-weld heat treatment so that weld metal, HAZ and base material develop uniform strength, toughness and corrosion resistance for demanding aerospace and high-integrity service.
Fabrication
Fabrication of 15-5PH Stainless Steel
15-5PH stainless steel (UNS S15500, 1.4545) is a precipitation-hardening martensitic stainless steel. It can be forged, machined and welded successfully, but all fabrication steps must be coordinated with the solution treatment + aging schedule to control strength, toughness and dimensional stability.
1. General Fabrication Approach
15-5PH is usually supplied in the solution-treated (annealed) condition.
Major forming, forging and rough machining are best done before final aging.
After aging to the required condition (e.g. H900, H1025, H1100), only light finishing cuts or grinding should be applied.
Because the alloy can reach very high strength, fabrication planning must consider distortion, residual stresses and final tolerances from the beginning.
2. Forming and Cold Working
Cold formability is limited compared with austenitic grades (304/316) but adequate for:
Light bending with generous radii
Straightening, sizing and minor geometry adjustments
Most cold work should be done in the solution-treated or softer aged condition, not in the highest-strength states.
Heavy cold work (e.g. large reductions, tight bends) should be followed by solution treatment and re-aging or at least stress relief to restore toughness and dimensional stability.
3. Hot Working and Forging
15-5PH can be hot worked and forged using standard stainless/high-alloy practices.
Forging is carried out in an appropriate high-temperature range, then:
Air cooled or controlled cooled
Solution treated to produce a uniform martensitic structure
Adequate reductions and proper temperature control help achieve a fine, even grain size, improving toughness and transverse properties.
After hot working and solution treatment, parts are ready for rough machining and later aging.
4. Machining
Machinability is moderate to good for a high-strength stainless steel.
Rough machining is best performed in the solution-treated or lower-strength aged condition.
After aging to final strength, use light finishing cuts or grinding only, to avoid excessive cutting forces and tool wear.
Good practice:
Rigid fixturing and sharp carbide tooling
Moderate speeds with adequate feed
Generous coolant for heat and chip control
5. Heat Treatment in the Fabrication Route
Heat treatment is central to the fabrication sequence:
Hot working (if any) → solution treatment → rough machining → aging (H900 / H1025 / H1100 etc.) → finish machining / grinding.
Aging at relatively low temperatures gives good dimensional stability, allowing tight tolerances after final heat treatment.
Aging condition is chosen to balance strength, toughness and stress-corrosion performance for the target application.
6. Welding as Part of Fabrication
When welding is required, it is normally done in the solution-treated condition.
After welding, the whole assembly is aged so weld metal, HAZ and base metal develop:
Similar strength
Compatible hardness and microstructure
Low-hydrogen procedures, controlled heat input and suitable fillers (15-5PH/17-4PH type or austenitic, depending on design) are important to minimise cracking and preserve toughness and corrosion resistance.
7. Dimensional Stability, Grinding and Surface Finishing
Because 15-5PH hardens by martensitic transformation and aging, distortion control is important:
Rough machine before final aging
Allow for small movements during heat treatment
Finish machine or grind after final aging.
The alloy can be ground and polished to very high surface quality, which is critical for:
Shafts and bearing seats
Valve and pump components
Precision mechanical parts and sealing surfaces
Proper removal of scale, oxides and machining marks also improves fatigue life and corrosion performance.
Summary
15-5PH stainless steel can be fabricated into high-strength, high-reliability components by performing most forming, forging and rough machining in the solution-treated condition, then applying the appropriate aging treatment and finishing with light machining or grinding, while carefully controlling welding procedures, residual stresses, distortion and surface quality to achieve the required mechanical properties and dimensional accuracy.
Hot Working
Hot Working of 15-5PH Stainless Steel
15-5PH stainless steel (UNS S15500, 1.4545) is a precipitation-hardening martensitic stainless steel that can be forged and hot worked successfully when temperature, reduction and cooling are properly controlled. Correct hot-working practice is important to obtain a fine, uniform structure before solution treatment and aging.
1. Recommended Hot Working Temperature Range
Typical hot-working / forging range: about 950–1,050°C (1,740–1,920°F)
Start deformation towards the upper end of this range for best plasticity.
Finish working above roughly 870°C (≈1,600°F) to avoid cracking as ductility decreases at lower temperatures.
Exact temperatures and soak times should follow the relevant mill or product specification.
2. Heating and Forging Practice
Heat the material slowly and uniformly through the section before heavy deformation.
Use firm, substantial reductions per pass (not light tapping) to promote good grain refinement.
For large forgings or complex shapes, reheat as soon as the temperature drops near the lower working limit.
Avoid long holding at the very top of the range to limit grain growth and scaling.
Correct forging practice prepares the microstructure for subsequent solution treatment and aging.
3. Cooling After Hot Working
After forging or hot forming, parts are usually cooled in still air or controlled conditions.
Hot working is normally followed by a full solution treatment to develop a uniform martensitic structure.
After solution treatment, the material is aged to the specified condition (H900, H1025, H1100, etc.) to achieve the required strength and toughness.
Very slow furnace cooling through the transformation range should be avoided when uniform high properties are required.
4. Surface Scale, Decarburisation and Cleanup
At forging temperatures, 15-5PH will develop oxide scale and may suffer some surface roughening.
Allow enough machining/grinding allowance to remove scale and any decarburised or damaged surface layer.
After hot working and solution treatment, use pickling, blasting or machining to restore a clean metallic surface.
Clean, sound surfaces are important for fatigue performance and corrosion resistance.
5. Influence on Microstructure and Mechanical Properties
Proper hot working in the correct temperature range produces a fine, uniform grain size.
A refined grain structure improves toughness, fatigue strength and transverse properties.
Insufficient reduction, overheating or working over too wide a temperature range can leave coarse or non-uniform grains, reducing toughness and consistency.
A subsequent solution treatment + aging is essential to reset the microstructure and fully develop the precipitation-hardening response.
6. Distortion, Cracking Control and Design Considerations
Design preforms and forgings with smooth transitions and uniform section thickness to reduce internal stresses.
Avoid sharp corners, abrupt section changes and heavy local reductions that can cause cracking during forging or cooling.
For long shafts or complex shapes, consider intermediate stress relief if very heavy reductions are applied.
Inspect forgings for laps, folds and surface cracks before committing to final heat treatment and machining to minimise scrap and rework.
Summary
Hot working of 15-5PH stainless steel is best carried out around 950–1,050°C with uniform heating, substantial reductions and air cooling, followed by solution treatment and aging; careful control of temperature, deformation and post-forging cleanup is essential to obtain a fine, consistent microstructure, minimise defects and deliver reliable high-strength properties in the finished components.
Heat Resistance
Heat Resistance of 15-5PH Stainless Steel
15-5PH stainless steel (UNS S15500, 1.4545) offers good heat resistance for a high-strength precipitation-hardening martensitic stainless steel. It is designed to retain useful strength and toughness at moderately elevated temperatures, but it is not a dedicated creep-resistant or high-temperature alloy.
1. Service Temperature Range
15-5PH is typically used in continuous service up to about 300–315°C (≈570–600°F).
Within this range it maintains a favourable combination of high tensile/yield strength and useful toughness.
Short-term or intermittent exposure to somewhat higher temperatures may be acceptable, but long-term operation much above this band is not recommended where strength is critical.
2. Effect of Aging Condition on Heat Resistance
Elevated-temperature behaviour depends strongly on the aging condition (H900, H1025, H1075, H1100, etc.):
Lower aging temperatures (e.g. H900)
Maximum room-temperature strength and hardness
More sensitive to toughness loss and overaging at elevated temperature
Intermediate aging (e.g. H1025 / H1075)
Slightly lower strength
Improved toughness and fatigue behaviour
Often a better compromise for parts that see both load and temperature
Higher aging temperatures (e.g. H1100 and above)
Lowest strength
Highest toughness and best stress-corrosion cracking resistance
More tolerant of moderate temperature exposure over time
In design, the continuous service temperature should be kept comfortably below the chosen aging temperature.
3. Strength and Toughness at Elevated Temperatures
As temperature rises, 15-5PH behaves like other steels:
Tensile and yield strength decrease with increasing temperature
Fatigue strength under cyclic loading is reduced
Impact toughness may fall, especially in the highest-strength conditions
Within its recommended temperature range, however, 15-5PH still provides significantly higher strength than standard austenitic grades and many conventional martensitic stainless steels.
4. Oxidation and Surface Behaviour
With about 15% Cr, 5% Ni and additions of Cu and Nb, 15-5PH has:
Better oxidation resistance than carbon and low-alloy steels at moderate temperatures
A stable chromium-rich oxide film in air and combustion gases within its normal service range
Its oxidation behaviour is not as strong as dedicated heat-resistant austenitic or nickel alloys at very high temperature, so it is best used where oxidation demands are moderate rather than extreme. Smooth, clean surfaces and avoidance of heavy scaling help maintain performance.
5. Overaging and Property Degradation
Prolonged exposure to temperatures near or above the aging temperature can:
Over-age the precipitate structure, lowering strength and hardness
Modify the martensitic/precipitate balance and reduce fatigue performance
Shift the strength–toughness balance away from the originally specified condition
For critical components, allowable stresses should take possible overaging into account if service temperatures approach the aging temperature for long periods.
6. Comparison with Other Stainless and High-Temperature Alloys
Compared with other steels:
Versus conventional martensitic stainless steels (410/420)
Much higher strength
Better toughness and similar or better heat resistance at moderate temperatures
Versus austenitic stainless steels (304/316)
Much higher room-temperature strength
Lower suitability for long-term, very high-temperature or creep-limited service
Versus dedicated heat-resistant austenitic or nickel alloys
15-5PH is not a substitute where continuous service at very high temperature and creep/oxidation resistance are primary requirements
It is best classed as a high-strength structural stainless steel with good moderate-temperature capability, not as a primary high-temperature alloy.
Summary
15-5PH stainless steel provides reliable heat resistance for structural and mechanical components operating at moderate temperatures (typically up to about 300–315°C / 570–600°F), retaining high strength and useful toughness with acceptable oxidation behaviour; however, prolonged exposure near or above its aging temperature leads to overaging and strength loss, so it should be used as a high-strength stainless steel with limited high-temperature capability rather than a dedicated creep- or scale-resistant alloy.
Machinability
Machinability of 15-5PH Stainless Steel
15-5PH stainless steel (UNS S15500, 1.4545) is a high-strength precipitation-hardening martensitic stainless steel with moderate machinability. It is generally more difficult to machine than 304/316, but easier than many tool steels when machined in the correct condition with suitable tooling and parameters.
1. General Machining Behaviour
15-5PH machines similarly to other PH martensitic stainless steels (e.g. 17-4PH).
It does not work harden as aggressively as austenitic grades, but its higher base strength means higher cutting forces and faster tool wear.
Machining should be planned as part of a route that uses the solution-treated or softer aged condition for roughing, and reserves high-strength conditions mainly for service, not heavy machining.
2. Preferred Conditions for Machining
Best machinability is achieved in the solution-treated (annealed) condition or in a relatively soft aging condition (e.g. higher aging temperature such as H1100).
Typical route:
Solution treatment → rough machining → aging to required condition (H900, H1025, H1100, etc.) → light finishing or grinding.
Machining directly in the highest-strength condition (e.g. H900) should be limited to light finishing passes, because cutting forces and tool wear are significantly higher.
3. Tooling and Cutting Parameters
Carbide tooling is recommended for most turning, milling and drilling operations.
Good practice includes:
Using insert grades designed for stainless / PH steels.
Applying moderate cutting speeds with sufficient feed to avoid rubbing.
Using positive rake, rigid toolholders and stiff setups to minimise chatter and edge chipping.
Avoiding very light “polishing” cuts that only generate heat and accelerate tool wear.
For small-batch or manual work, high-quality HSS or cobalt HSS tools can be used at appropriately reduced speeds.
4. Coolant Use and Chip Control
Effective coolant and chip management are important for tool life and surface quality:
Use plenty of cutting fluid or coolant to control temperature, improve surface finish and reduce built-up edge.
In milling and drilling, ensure coolant reaches the cutting zone, especially for deep holes.
15-5PH can produce relatively tough, continuous chips; use chip-breaker inserts and adjust feed and depth of cut to promote chip breaking.
Good chip control reduces the risk of surface damage, improves reliability of automatic operations and helps maintain dimensional accuracy.
5. Drilling, Tapping and Threading
For drilling operations:
Use carbide or cobalt HSS drills with steady feed and appropriate point geometry.
Apply peck cycles for deep holes to clear chips and maintain cooling.
For tapping and threading:
Use strong, premium taps with abundant lubrication in higher-strength conditions.
Where possible, consider thread milling for critical or large threads to reduce risk of tap breakage and to better control thread fit.
Allow for some elastic recovery (spring-back) due to high strength when setting thread and bore tolerances.
6. Surface Finish, Distortion and Dimensional Control
15-5PH can be finished to very high surface quality by turning, grinding and polishing, which is important for:
Shafts and bearing seats
Valve stems and sealing surfaces
Precision mechanical components and fits
To maintain dimensional control:
Use a route such as rough machining → aging → finish machining / grinding with light cuts.
Avoid overheating during machining or grinding to prevent local tempering, microcracking or unwanted residual tensile stresses.
Use balanced machining and rigid fixturing, especially for long or slender parts, to minimise distortion when the material is aged to high strength.
Summary
The machinability of 15-5PH stainless steel is moderate: it machines best in the solution-treated or softer aged conditions using rigid setups, carbide tooling, conservative speeds with adequate feed, effective coolant and good chip control, followed by light finishing or grinding after aging to achieve accurate dimensions and high-quality surfaces on high-strength shafts, gears, fasteners, valve components and other precision parts.
Corrosion Resistance
Corrosion Resistance of 15-5PH Stainless Steel
15-5PH stainless steel (UNS S15500, 1.4545) offers good corrosion resistance for a high-strength martensitic precipitation-hardening stainless steel, broadly similar to 17-4PH and clearly better than conventional martensitic grades such as 410 / 420, though generally below 316 in very aggressive chloride or chemical environments.
1. General Corrosion Behaviour
Designed to combine high strength and stainless corrosion resistance in one alloy.
Performs well in many atmospheric, fresh-water and mildly corrosive industrial environments.
Compared with carbon and low-alloy steels, 15-5PH shows much lower rusting and staining under the same conditions.
2. Atmospheric and Fresh-Water Environments
Good resistance to rusting and discoloration in rural, urban and light industrial atmospheres.
Suitable for fresh water, cooling water and many industrial waters with moderate chloride levels.
Commonly used for shafts, fasteners, valve/pump parts and structural hardware exposed to humidity, splash, wash-down and condensation.
3. Marine and Chloride-Containing Service
In marine atmospheres and splash zones, 15-5PH performs better than carbon steel and standard martensitic stainless.
However, its pitting/crevice corrosion resistance in chlorides is roughly comparable to 17-4PH and generally below molybdenum-bearing austenitic grades such as 316.
For continuous immersion in seawater, hot concentrated brines or stagnant chloride crevices, more highly alloyed austenitic or duplex stainless steels are usually preferred.
4. Behaviour in Chemical and Process Environments
Suitable for many mild to moderately corrosive chemical media, including:
Light acids and alkalis at controlled concentration and temperature
Fuels, oils and many organic fluids
Process plant environments where both strength and moderate corrosion resistance are required
Not recommended for:
Strong mineral acids or strong reducing acid environments
Hot, concentrated chloride solutions
Service where maximum pitting/crevice or acid resistance is required (nickel alloys or highly alloyed stainless grades are more appropriate).
5. Stress-Corrosion Cracking and Hydrogen Effects
As a high-strength precipitation-hardening steel, 15-5PH is more sensitive to chloride stress-corrosion cracking (SCC) than low-strength austenitic grades.
SCC risk increases with:
High tensile stress (residual + applied)
Elevated temperature
Chloride-bearing environments
Processes that introduce hydrogen (e.g. acid pickling, electroplating, excessive cathodic protection) can promote hydrogen embrittlement if not properly controlled.
Good practice: limit unnecessary high-strength conditions in severe environments, control residual stress, and manage any hydrogen-charging operations carefully.
6. Influence of Heat Treatment and Microstructure
Corrosion performance is closely tied to the solution treatment + aging condition:
Proper solution treatment and standard aging give a uniform martensitic + precipitate structure with consistent behaviour.
Very low-temperature, maximum-strength aging conditions may slightly increase susceptibility to SCC compared with softer conditions that provide higher toughness.
Non-standard or badly controlled heat treatments (overaging, mixed structures, local overheating) can reduce both toughness and corrosion performance, especially near welds or heavily worked areas.
7. Surface Finish, Cleanliness and Design
As with all stainless steels, surface condition strongly affects corrosion resistance:
Smooth, ground or polished surfaces resist pitting and crevice attack better than rough, damaged or heavily machined surfaces.
Weld heat tint, scale, slag and embedded iron should be removed by pickling, grinding or blasting and followed by proper cleaning/passivation.
Good design reduces corrosion risk by:
Avoiding tight crevices, stagnant pockets and water traps
Providing smooth weld profiles and transitions
Ensuring drainage and ease of cleaning in service
Summary
15-5PH stainless steel provides good general corrosion resistance and clearly superior performance to conventional martensitic steels, with behaviour broadly comparable to 17-4PH: it works well in atmospheric, fresh-water and many industrial environments, and in moderate marine or chemical service, but does not match the chloride or acid resistance of highly alloyed austenitic or duplex stainless steels, so it is best used where a high-strength, moderately corrosion-resistant structural alloy is required rather than as a primary material for the most aggressive corrosive conditions.
Heat Treatment
Heat Treatment of 15-5PH Stainless Steel
15-5PH stainless steel (UNS S15500, 1.4545) is a precipitation-hardening martensitic stainless steel. Its final mechanical properties are controlled almost entirely by the solution treatment + aging (“H”) condition, so the heat-treat schedule is a core part of component design and fabrication.
1. Objectives of Heat Treatment
Produce a uniform martensitic structure suitable for precipitation hardening
Develop high tensile and yield strength with controlled hardness
Adjust toughness, fatigue performance and stress-corrosion behaviour via aging temperature
Minimise residual stress and distortion from forging, machining and welding
2. Solution Treatment (Austenitizing / Annealing)
Purpose:
Dissolve alloying elements into austenite
Homogenise the structure before martensitic transformation and aging
Typical practice (exact temperature/time must follow the applicable spec, e.g. AMS 5659):
Heat into the austenitizing range (high temperature, around the 15-5PH solution-treat band)
Hold long enough for through-heating of the section
Cool rapidly (usually air cool, sometimes oil/quench-gas depending on section and spec) to form a martensitic matrix
After solution treatment, 15-5PH is:
At moderate strength and hardness
Reasonably machinable for roughing
Ready for welding, straightening and subsequent aging
3. Aging / Precipitation-Hardening Conditions
After solution treatment, 15-5PH is aged to develop final properties. Common “H” conditions include, for example:
H900 – low aging temperature, maximum strength and hardness
H1025 / H1075 – intermediate strength with improved toughness
H1100 (and higher) – lower strength, maximum toughness and better stress-corrosion performance
General procedure:
Reheat to the specified aging temperature
Hold for the specified time (typically a few hours)
Cool in still air
During aging, fine copper-rich precipitates and carbides form in the martensitic matrix, greatly increasing yield/tensile strength and tuning toughness.
4. Effect of Aging Temperature on Properties
Low-temperature aging (H900)
Very high yield and tensile strength
High hardness
Lower but still useful toughness and damage tolerance
Intermediate aging (H1025 / H1075)
Slightly reduced strength and hardness
Better toughness and fatigue performance
Often chosen for high-integrity structural and landing-gear parts
High-temperature aging (H1100 and above)
Further reduction in strength
Maximum toughness and best stress-corrosion cracking resistance
Used where environment and damage tolerance dominate over peak strength
The designer selects the condition according to the required strength–toughness–environment balance.
5. Stress Relief and Post-Weld Heat Treatment
Stress relief
May be applied after heavy machining, straightening or forming
For corrosion-critical parts, a full solution + aging schedule is usually preferred over low-temperature stress relief alone
Post-weld heat treatment (PWHT)
Welding is normally done in the solution-treated condition
After welding, the entire assembly is aged to the specified “H” condition
PWHT/aging:
Restores high strength in weld metal and HAZ
Helps equalise hardness and microstructure across the joint
Reduces residual stresses from welding
Some critical specifications may call for re-solution + aging after welding; others allow direct aging from the as-welded solution-treated state.
6. Typical Production Heat-Treatment Sequences
Common practical routes are:
Forged parts / large sections
Forge / hot work
Air cool
Solution treat
Rough machining
Age (H900 / H1025 / H1100 etc.)
Finish machining / grinding
Welded fabrications
Solution-treated material
Weld with approved procedure
Age entire assembly to required condition
Final machining, sizing and surface finishing
Precision high-tolerance components
Solution treat
Rough machine
Age to final condition
Light finish machining / grinding to final size and surface finish
7. Precautions During Heat Treatment
Avoid overheating during solution treatment to prevent grain coarsening and toughness loss
Ensure accurate furnace control and adequate soak time for heavy sections
Do not exceed specification limits on the number of solution/aging cycles
Support and fixture long or thin parts carefully during heating and cooling to minimise distortion
Summary
Heat treatment of 15-5PH stainless steel is based on solution treatment to form a martensitic matrix, followed by controlled aging (H900, H1025, H1075, H1100, etc.) to tune strength, hardness, toughness and stress-corrosion behaviour; by integrating welding, stress relief and machining with this solution-plus-aging schedule, engineers can produce high-strength, dimensionally stable components with properties matched to demanding aerospace and high-integrity mechanical applications.
Cold Working
Cold Working of 15-5PH Stainless Steel
15-5PH stainless steel (UNS S15500, 1.4545) is a high-strength precipitation-hardening martensitic stainless steel with limited cold workability compared with austenitic grades such as 304/316. Cold working is possible but should be kept to light or moderate deformation and always coordinated with the heat-treatment and aging schedule.
1. General Cold Workability
15-5PH has lower ductility than austenitic stainless steels, especially in high-strength aged conditions (e.g. H900).
It can tolerate modest cold deformation for straightening, sizing and minor shape adjustment.
Heavy cold forming, tight-radius bending or deep drawing are generally not recommended, particularly on thick or fully hardened sections.
2. Preferred Condition for Cold Working
Cold working should primarily be carried out in the:
Solution-treated (annealed) condition, or
A softer, higher-temperature aged condition (e.g. H1100), where ductility is better.
In these states, the risk of cracking and excessive work hardening is reduced.
In maximum-strength conditions (H900, H1025), cold work should be restricted to very small corrections only (slight straightening, minor tweaking).
3. Typical Cold Working Operations
Suitable cold-working operations for 15-5PH include:
Straightening of bars, shafts and pins after heat treatment or machining
Light bending with generous radii on plates, flats or bars
Cold sizing, light swaging or small diameter reductions where total strain is limited
Generally unsuitable (except perhaps in very thin sections) are:
Severe cold heading with large upset ratios
Tight-radius bending of thick sections
Complex deep drawing or heavy press-forming operations
4. Effects on Mechanical Properties and Residual Stresses
Cold work in 15-5PH:
Increases local strength and hardness
Reduces ductility and toughness in heavily strained regions
Introduces residual stresses, which can affect:
Fatigue performance
Dimensional stability
Stress-corrosion cracking behaviour
Because 15-5PH already relies on a controlled precipitation-hardened martensitic structure, uncontrolled or heavy cold deformation can make properties non-uniform through the section.
5. Stress Relief and Heat Treatment After Cold Work
After significant cold deformation, some form of heat treatment is usually advisable:
For major cold work, best practice is often:
Cold form → solution treat → age to final condition
to restore a uniform microstructure and consistent properties.For moderate adjustments in an already aged condition, a low-temperature stress-relief treatment may help reduce residual stresses without fully resetting strength, if allowed by specification.
Critical, highly loaded components should not rely on heavily cold-worked, unrelieved material in service.
6. Design and Process Recommendations
To use cold working safely and effectively on 15-5PH:
Plan for most forming operations to occur before final aging.
Use large bend radii and gradual transitions to reduce local strain and avoid cracking.
Avoid sharp corners, notches and abrupt section changes in areas that will be cold worked.
For tight tolerances and critical parts, a typical route is:
Rough shaping / light cold work → solution treatment → aging → finish machining / grinding.
Summary
Cold working of 15-5PH stainless steel should be limited to light to moderate operations such as straightening, sizing and gentle bending, carried out mainly in the solution-treated or softer aged conditions; heavier deformation can harm toughness and introduce detrimental residual stresses, so any significant cold work should be followed by appropriate stress relief or full solution treatment and aging to recover a uniform, reliable high-strength microstructure for demanding aerospace and high-integrity mechanical applications.
