Stainless Steel, Precipitation Hardening
AMS 5629 (13-8)
A precipitation hardenable chromium-nickel-molybdenum martensitic stainless grade.
Precipitation hardening steels are characterised into one of three groups based on their final microstructures after heat treatment. The three types are: martensitic, semi-austenitic and austenitic.
Martensitic precipitation hardening stainless steels have a predominantly austenitic structure at annealing temperatures of around 1040 to 1065°C. Upon cooling to room temperature, they undergo a transformation that changes the austenite to martensite.
AMS5629 (13-8) is a martensitic precipitation hardening stainless steel. Heat treatment provides 13-8 with high strength. It comes in various conditions offering an array of properties. Good transverse toughness properties are achieved by tight chemical composition control, low carbon content, and vacuum melting.
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AMS 5629 (13-8) Related Specifications
| System / Standard | Country / Region | Grade / Designation |
| UNS | International | S13800 |
| Common name | International | 13-8Mo / PH 13-8Mo / 13-8 PH |
| AISI / ASTM | USA | 13-8Mo (Type XM-13) |
| AMS | USA / Aerospace | AMS 5629 (bars, forgings, wire, tubing, rings, extrusions) |
| AMS | USA / Aerospace | AMS 5864 (plate, sheet, strip) |
| EN / W.Nr. | Europe | 1.4534 |
| EN Name | Europe | X3CrNiMoAl13-8-2 |
| JIS | Japan | SUS XM-13 |
| GB | China | 0Cr13Ni8Mo2Al (PH13-8Mo) |
Properties
Chemical Composition
| Chemical Element | % Present |
| Carbon (C) | 0.00 - 0.05 |
| Chromium (Cr) | 12.25 - 13.25 |
| Manganese (Mn) | 0.00 - 0.10 |
| Silicon (Si) | 0.00 - 0.10 |
| Phosphorous (P) | 0.00 - 0.01 |
| Sulphur (S) | 0.00 - 0.01 |
| Nickel (Ni) | 7.50 - 8.50 |
| Molybdenum (Mo) | 2.00 - 2.50 |
| Aluminium (Al) | 0.90 - 1.35 |
| Nitrogen (N) | 0.00 - 0.01 |
| Iron (Fe) | Balance |
Mechanical Properties
Mechanical Properties of AMS 5629 (13-8PH) Stainless Steel
| Condition | Tensile Strength (MPa) | 0.2% Proof Stress (MPa) | Elongation (% on 4D) | Hardness (HRC) |
| H950 | 1,517 | 1,413 | 10 | 45 |
| H1000 | 1,413 | 1,310 | 10 | 43 |
| H1025 | 1,276 | 1,207 | 11 | 41 |
| H1050 | 1,207 | 1,138 | 12 | 40 |
| H1100 | 1,034 | 931 | 14 | 34 |
| H1150 | 931 | 621 | 14 | 30 |
General Physical Properties
| Physical Property | Value |
| Density | 7.75 g/cm³ |
| Thermal Expansion | 10.8 x 10-6/K |
| Modulus of Elasticity | 196 GPa |
| Thermal Conductivity | 18.4 W/m.K |
| Electrical Resistivity | 0.8 x 10-6 Ω .m |
Applications of AMS 5629 (13-8PH) Stainless Steel
AMS 5629 (13-8PH / PH 13-8Mo, UNS S13800) is a high-strength, precipitation-hardening martensitic stainless steel used where a combination of high strength, toughness, corrosion resistance and resistance to stress-corrosion cracking is required, especially up to about 600°F (316°C).
1. Aerospace Structural and Landing Gear Components
Structural airframe parts and large airframe components requiring high transverse toughness
Landing gear components, pins and highly loaded fittings
Engine and control-system components exposed to cyclic loading and moderate temperatures
Hardware requiring high strength with good resistance to stress-corrosion cracking in flight environments
2. High-Strength Shafts, Pins and Power-Transmission Parts
Shafts and rotors used in aerospace and industrial drives
High-strength pins, lockwashers and couplings
Precision power-transmission elements where uniform properties in longitudinal and transverse directions are important
Components that must retain high strength and toughness after low-temperature aging
3. Fasteners, Fittings and Valve Components
Cold-headed and machined fasteners (bolts, screws, studs) requiring very high strength and good corrosion resistance
High-integrity fittings and connectors for aerospace and process industries
Valve parts, stems and seats operating in mildly to moderately corrosive media with high stress levels
4. Petrochemical, Nuclear and Power-Generation Equipment
Components in petrochemical plants where high strength and stress-corrosion cracking resistance are critical
Parts for nuclear reactor and auxiliary systems (valves, fittings, structural elements)High-stress components in power-generation equipment, including pumps, shafts and hardware at moderate temperatures
5. Injection Molding, Tooling and Industrial Machinery
Injection molding equipment components such as tie bars, platens, and high-strength tooling inserts
Waterjet cutting components and slide gates for flow control, where high strength combines with corrosion resistance
Precision parts in industrial machinery that must maintain mechanical properties after aging treatment
6. Defense and High-Integrity Engineering Components
Missile and defence-related components needing high strength and good fracture toughness
Critical hardware in demanding environments where failure is not acceptable and properties must be consistent in all directions
Components where high strength + stress-corrosion cracking resistance are mandatory design requirements
Summary
AMS 5629 (13-8PH) stainless steel is used for high-strength, high-integrity components such as aerospace structural parts and landing gear, shafts and pins, fasteners and fittings, valve and reactor components, injection molding and water-control equipment, and critical defence and industrial hardware, wherever a combination of very high strength, good toughness, corrosion resistance and resistance to stress-corrosion cracking is required up to about 600°F (316°C).
Characteristics of AMS 5629 (13-8PH) Stainless Steel
AMS 5629 (13-8PH / PH 13-8Mo, UNS S13800, EN 1.4534 / X3CrNiMoAl13-8-2) is a vacuum-melted, precipitation-hardening martensitic stainless steel. It is designed to provide very high strength, excellent toughness (including transverse toughness), good corrosion resistance and outstanding resistance to stress-corrosion cracking, especially in the aged condition up to about 600°F (316°C).
1. Precipitation-Hardening Martensitic Stainless Steel
AMS 5629 specifies a Cr–Ni–Mo–Al precipitation-hardening martensitic stainless steel.
It develops high strength through a combination of martensitic transformation and controlled precipitation hardening (aging).
The nominal composition includes approximately 13% Cr, 8% Ni, 2% Mo and Al additions to form strengthening precipitates.
The grade is supplied as VAR or VIM-VAR remelted bar, wire, forgings and rings for high-integrity applications.
2. Very High Strength in Aged Conditions
After solution treatment and aging (e.g. H950, H1000, H1050, etc.), 13-8PH provides:
Very high tensile strength, typically exceeding 1,300–1,500 MPa in the higher-strength aging conditions (e.g. H950/H1000).
High 0.2% proof (yield) strength, suitable for highly loaded structural and mechanical components.
Strength levels that can be tailored by choosing different aging temperatures, allowing optimisation for either higher strength or higher toughness.
These strength levels make AMS 5629 suitable for critical aerospace and high-performance mechanical parts where weight reduction and compact design are important.
3. Excellent Toughness and Transverse Properties
A key feature of AMS 5629 (13-8PH) is its excellent toughness, including both longitudinal and transverse directions.
The VAR / VIM-VAR remelting route provides very low inclusion levels and high cleanliness.
The alloy is designed to minimise segregation and achieve good isotropy of mechanical properties.
Under appropriate aging conditions, 13-8PH exhibits high Charpy impact energy and good fracture toughness, even at relatively high strength levels.
This combination of high strength and good transverse toughness is a major reason for its extensive use in aerospace structural and landing gear applications.
4. Good Corrosion Resistance and SCC Resistance
Compared with conventional martensitic stainless steels, 13-8PH offers:
Corrosion resistance comparable to or slightly better than 17-4PH in many environments.
Good resistance to general atmospheric and industrial corrosion.
Excellent resistance to stress-corrosion cracking (SCC) in many chloride-containing environments, especially when properly aged.
This makes AMS 5629 suitable for service in mildly to moderately corrosive environments where high stress, cyclic loading and potential SCC are design concerns.
5. Stable Mechanical Properties up to Moderate Temperatures
AMS 5629 (13-8PH) is designed to retain useful mechanical properties at elevated temperatures:
High strength and toughness are maintained up to approximately 600°F (316°C) service temperatures.
Aging treatments are carried out at relatively low temperatures, giving good dimensional stability and predictable property levels.
Over-aging at significantly higher temperatures will gradually reduce strength but can further improve toughness and stress-corrosion resistance, depending on the application.
This balance makes the alloy attractive for components exposed to moderate heat in aerospace and power-generation systems.
6. Controlled Heat Treatment and Aging Response
13-8PH responds strongly and predictably to heat treatment:
Solution treatment (austenitizing) followed by rapid cooling produces a martensitic structure with good baseline strength.
Aging at specific temperatures (e.g. H950, H1000, H1025, H1050, H1100, H1150) allows precise control of tensile strength, yield strength, toughness and hardness.
Lower aging temperatures (e.g. H950) give maximum strength, while higher aging temperatures (e.g. H1100/H1150) provide lower strength but improved toughness and SCC resistance.
This tunable response allows engineers to select the most suitable condition for each component’s performance requirements.
7. Good Fabrication and Machining Characteristics for a High-Strength Alloy
For a very high-strength stainless steel, AMS 5629 has relatively good fabrication characteristics:
It can be hot worked and forged using standard high-alloy practices, followed by solution treatment and aging.
Machinability is generally better than many high-alloy tool steels when machining is performed in the solution-treated or lower-strength aged conditions.
Weldability is possible with appropriate procedures, though—as with other high-strength martensitic PH grades—careful control of heat input and subsequent aging is required to maintain properties and avoid cracking.
Overall, it offers a useful compromise between strength, toughness, corrosion resistance and manufacturability.
8. Aerospace-Grade Quality and Reliability
AMS 5629 is an aerospace material specification, so the alloy is produced under stringent quality controls:
Vacuum remelting and strict cleanliness requirements.
Tight control of chemistry, microstructure and heat treatment.
Consistent mechanical properties within and between heats, including transverse directions.
This ensures high reliability and traceability for components used in flight-critical and safety-critical systems.
Summary
AMS 5629 (13-8PH) stainless steel is a high-strength, precipitation-hardening martensitic stainless alloy that combines very high tensile and yield strength with excellent toughness (including transverse toughness), good corrosion and stress-corrosion cracking resistance, stable properties up to about 600°F and reliable aerospace-grade quality, making it ideal for critical structural, landing gear, shaft, fastener and high-integrity mechanical components.
Additional Information
Weldability
Weldability of AMS 5629 (13-8PH) Stainless Steel
AMS 5629 (13-8PH) is weldable, but like other high-strength martensitic precipitation-hardening stainless steels, it is not a “simple” welding grade. Achieving reliable welds requires strict control of procedure, filler selection and post-weld heat treatment to maintain strength, toughness and corrosion resistance.
1. General Weldability Characteristics
13-8PH can be welded by common fusion processes, but it should always be treated as a high-strength, crack-sensitive material, not like 304/316.
Without proper procedure (preheat, controlled heat input, correct aging), welds may suffer from loss of toughness, distortion, or cracking.
For critical aerospace/defence components, qualified welding procedures and testing (WPS/PQR) are essential.
2. Suitable Welding Processes
Typical welding processes for AMS 5629 include:
Gas Tungsten Arc Welding (GTAW / TIG) for high-quality, low-heat-input joints
Gas Metal Arc Welding (GMAW / MIG) for production welding with controlled parameters
Shielded Metal Arc Welding (SMAW) using appropriate low-hydrogen consumables
Electron beam or laser welding for precision joints with minimal distortion
Process choice depends on section thickness, required quality level and access to the joint.
3. Filler Metal Selection
Filler selection must consider required strength, toughness and corrosion performance:
Matching or near-matching fillers (13-8PH / similar PH stainless) are used where matching strength and aging response are required.
Austenitic stainless fillers (such as 300-series) can be used in some cases to improve weld toughness and crack resistance, especially for dissimilar joints or highly restrained welds, but will not match base-metal strength.
For aerospace and high-integrity work, filler must comply with the relevant AMS or equivalent specification and be used with a qualified procedure.
4. Preheat and Interpass Temperature Control
Although 13-8PH is less crack-sensitive than many conventional martensitic steels, good thermal control is still important:
Moderate preheat is often recommended for thicker or highly restrained joints to reduce thermal gradients and hydrogen cracking risk.
Interpass temperature should be controlled to avoid excessive heat input that could coarsen the microstructure or distort the aging response.
Overheating and multiple high-heat passes should be avoided wherever possible.
5. Post-Weld Heat Treatment and Aging
Post-weld heat treatment is a key part of welding 13-8PH:
Welds are usually made in the solution-treated (unaged) condition, followed by aging to bring both weld metal and base metal to the desired condition (H950, H1000, H1050, etc.).
Aging after welding restores high strength and toughness in the heat-affected zone and weld metal, and helps relieve residual stresses.
For some less critical applications, stress-relief or modified aging cycles may be used, but critical aerospace parts generally follow the full specified solution + age sequence.
6. Control of Cracking and Distortion
Even with good weldability for a high-strength alloy, precautions are necessary:
Use low-hydrogen procedures (dry consumables, clean joint surfaces, proper gas shielding).
Minimise joint restraint and avoid sharp transitions or stress concentrators at weld toes.
Design joints and fixtures to control distortion during welding and subsequent aging.
Non-destructive examination (e.g. PT, MT, UT or RT, depending on thickness and criticality) is commonly applied to verify weld soundness.
7. Effect of Welding on Mechanical and Corrosion Properties
Improper welding can significantly reduce performance:
Overheating, incorrect filler or missing PWHT can lead to reduced toughness, inconsistent strength and lower resistance to stress-corrosion cracking.
Correctly welded and aged joints, however, can achieve properties close to those of the base metal, with good transverse toughness and corrosion resistance.
For components in aggressive or chloride-bearing environments, weld quality and surface finishing (smooth, defect-free weld beads) are particularly important.
Summary
AMS 5629 (13-8PH) stainless steel is weldable, but must be treated as a high-strength precipitation-hardening martensitic alloy: successful welding relies on suitable process choice, careful control of heat input, use of appropriate filler metals, and a proper post-weld aging or heat-treatment cycle to deliver welds with the required strength, toughness and corrosion resistance for critical aerospace and high-integrity applications.
Fabrication
Fabrication of AMS 5629 (13-8PH) Stainless Steel
AMS 5629 (13-8PH) is a high-strength precipitation-hardening martensitic stainless steel. It can be forged, machined and welded successfully when its hardenable nature and aging response are properly controlled throughout the fabrication sequence.
1. Forming and Cold Working
Cold formability of 13-8PH is limited compared with austenitic stainless steels.
It is best to perform any bending, straightening or light cold sizing in the solution-treated (unaged) or lower-strength aged condition, where ductility is higher.
Heavy cold deformation, deep drawing or tight-radius bending are generally not recommended; if significant cold work is applied, a subsequent solution treatment and re-aging or at least stress relief is advisable to restore toughness and dimensional stability.
2. Hot Working and Forging
AMS 5629 products are usually hot worked and forged at elevated temperatures using standard high-alloy practices.
Forging is carried out in the appropriate hot-working range, followed by air cooling or controlled cooling and then solution treatment to produce a uniform martensitic structure.
After hot working, components are normally solution treated and aged to the required condition (e.g. H950, H1000, H1050), ensuring consistent strength and toughness throughout the section.
3. Machining
Machinability of 13-8PH is moderate for a very high-strength stainless alloy.
Best results are obtained when rough machining is done in the solution-treated or lower-strength aged condition, followed by aging to final properties and light finishing cuts or grinding.
Use rigid setups, sharp carbide tooling, relatively modest cutting speeds and adequate feed rates, together with generous coolant, to control heat and tool wear and to achieve high-quality surfaces on shafts, pins, fittings and precision components.
4. Heat Treatment in the Fabrication Route
Heat treatment is central to the fabrication of AMS 5629 components.
A typical route is: hot working → solution treatment → rough machining → aging to the chosen condition → finish machining and grinding.
The aging temperature (H950, H1000, H1050, etc.) is selected to balance strength, toughness and stress-corrosion resistance; all welded or heavily cold-worked parts should be included in the appropriate solution + aging cycle to ensure uniform properties.
5. Welding in Fabrication
13-8PH can be welded as part of fabrication when suitable procedures are used.
Welds are usually made in the solution-treated condition, then the entire assembly is aged so that weld metal, heat-affected zone and base metal achieve the required mechanical properties.
Low-hydrogen practice, controlled heat input and qualified fillers are important to minimise distortion, avoid cracking and maintain toughness and corrosion resistance in critical aerospace and high-integrity components.
6. Dimensional Stability, Grinding and Finishing
Because 13-8PH develops high strength through martensitic transformation and aging, distortion control is important in fabrication.
Good practice includes: rough machining before final aging, stress-relief or full solution + aging after heavy machining or welding, and finish grinding or machining after the final heat treatment.
The alloy can be ground and polished to very high surface quality, which is essential for shafts, sealing surfaces, bearing fits and precision mechanical parts.
Summary
AMS 5629 (13-8PH) stainless steel can be fabricated into high-strength, high-reliability components by combining controlled hot working, limited cold forming, carefully planned machining, appropriate solution treatment and aging, and properly qualified welding procedures, with particular attention to distortion and stress control so that the final parts achieve the required strength, toughness and corrosion performance.
Hot Working
Hot Working of AMS 5629 (13-8PH) Stainless Steel
AMS 5629 (13-8PH) is a precipitation-hardening martensitic stainless steel that can be forged and hot worked efficiently when temperature, reduction and cooling are carefully controlled. Proper hot working practice is important to achieve a clean, fine-grained structure before solution treatment and aging.
1. Recommended Hot Working Temperature Range
Hot working and forging are normally carried out in a moderate high-temperature range to balance ductility and grain control:
Typical heating/forging range: about 950–1,040°C (1,750–1,900°F)
Start deformation towards the upper end of this range for best plasticity.
Finish working above roughly 815°C (1,500°F) to avoid cracking from low ductility at lower temperatures.
These ranges are approximate and should be aligned with the specific mill or specification recommendations for the product form.
2. Forging and Reheating Practice
During hot working:
Heat uniformly through the section before applying heavy deformation.
Use firm, significant reductions per pass (not light tapping) to promote good grain refinement.
For large forgings or complex shapes, return the part to the furnace as soon as the temperature drops near the lower working limit.
Avoid prolonged soaking at the very top of the range, which can cause grain coarsening and excessive scale formation.
Well-controlled forging sets up the microstructure for subsequent solution treatment and aging.
3. Cooling After Hot Working
After hot working or forging:
Cool in still air or controlled conditions unless a specific procedure requires otherwise.
Follow hot working with a solution treatment (austenitizing) to restore a uniform martensitic structure, then age to the required condition (such as H950, H1000, H1050, etc.).
Avoid very slow furnace cooling through the transformation range if high strength and toughness are needed, as this can lead to non-uniform structures and variable properties.
The typical sequence is: forge → air cool → solution treat → age.
4. Surface Protection and Scale Removal
At forging temperatures, 13-8PH will form oxide scale:
Allow sufficient machining/grinding allowance to remove scale and any decarburised surface layer after hot working.
Where possible, use protective atmospheres or coatings in furnaces to limit scale formation on critical surfaces.
After forging and prior to final machining, apply shot blasting, grinding or machining to restore a clean, sound surface.
Clean, scale-free surfaces are important for both fatigue performance and corrosion resistance.
5. Effect on Microstructure and Subsequent Heat Treatment
The hot working operation strongly influences the final microstructure:
Adequate, properly controlled reductions help produce a fine, uniform grain size, improving strength, toughness and isotropy.
Excessive working at too high temperature or with insufficient reduction can leave a coarse or non-uniform grain structure, which may reduce toughness—especially in the transverse direction.
A full solution treatment after hot working resets the microstructure before aging; aging then develops the required precipitation-hardened martensitic structure and mechanical properties.
Thus, hot working, solution treatment and aging must be viewed as a linked sequence, not isolated steps.
6. Distortion and Defect Control
Good practice during hot working helps minimise internal defects and later distortion:
Design preforms with smooth transitions and even section thickness to reduce internal stresses.
Avoid sharp corners and abrupt changes in cross-section that can initiate cracks during forging or cooling.
Inspect forgings for laps, folds, surface cracks and internal defects before committing to expensive machining and heat treatment.
For long shafts or complex shapes, consider intermediate normalising or stress relief before final solution treatment if heavy reductions have been applied.
This reduces scrap risk and improves dimensional control after final aging.
Summary
Hot working of AMS 5629 (13-8PH) stainless steel is best carried out in a controlled range around 950–1,040°C (1,750–1,900°F) 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 achieve a fine, uniform microstructure, minimise defects and ensure high, isotropic mechanical properties in the finished high-strength components.
Heat Resistance
Heat Resistance of AMS 5629 (13-8PH) Stainless Steel
AMS 5629 (13-8PH) stainless steel offers good heat resistance for a high-strength precipitation-hardening (PH) martensitic alloy. It is designed to retain useful strength and toughness at moderately elevated temperatures, but it is not a dedicated high-temperature or creep-resistant alloy.
1. Service Temperature Range
At room temperature and up to moderate temperatures, 13-8PH maintains very high tensile and yield strength with good toughness.
It is commonly used in applications with service temperatures up to about 600°F (≈315–320°C), depending on the selected aging condition.
Above this range, strength and toughness begin to degrade more rapidly, and the alloy is generally not recommended for long-term high-temperature or creep-limited service.
2. Effect of Aging Condition on Heat Resistance
Mechanical properties at elevated temperature depend strongly on the aging condition (H950, H1000, H1050, H1100, H1150, etc.).
Lower aging temperatures (e.g. H950) provide maximum strength at room temperature, but the usable service temperature may be more limited by overaging and loss of toughness.
Higher aging temperatures (e.g. H1100, H1150) give lower strength but improved toughness and stress-corrosion resistance, and they can be more stable under prolonged exposure to moderately elevated temperatures.
Selecting an aging condition that balances strength, toughness and thermal stability is essential for parts exposed to heat.
3. Strength and Toughness at Elevated Temperatures
As temperature increases, 13-8PH—like most steels—shows:
Decreasing tensile and yield strength
Reduced fatigue strength under cyclic loading
Some loss of impact toughness, which may be more pronounced in the highest-strength (lowest aging temperature) conditions
However, within its recommended range (up to around 600°F), 13-8PH retains a favourable combination of high strength and useful toughness, which is one reason it is widely used in aerospace and power-related components that see moderate heat.
4. Oxidation and Surface Behaviour at Temperature
With about 13% chromium and added nickel and molybdenum, 13-8PH has better oxidation resistance than carbon or low-alloy steels at moderate temperatures.
It forms a protective oxide film in air, but its high-temperature oxidation resistance is not as strong as that of fully austenitic heat-resistant stainless steels designed for continuous service at higher temperatures.
For components operating at elevated temperature, maintaining smooth, clean surfaces and avoiding heavy scaling or roughness helps preserve fatigue performance and corrosion/oxidation resistance.
5. Overaging and Property Degradation
Exposure to temperatures near or above the aging temperature for extended periods can gradually:
Over-age the precipitate structure, reducing strength and hardness
Modify the microstructure in ways that affect fatigue and stress-corrosion performance
Change the balance between strength and toughness compared with the original aged condition
In design, it is good practice to keep the continuous service temperature safely below the chosen aging temperature and to consider possible overaging effects when setting allowable stresses and inspection intervals.
6. Comparison with Other Stainless and High-Temperature Alloys
Compared with conventional martensitic stainless steels, 13-8PH offers:
Much higher strength
Better toughness and stress-corrosion resistance
Comparable or better heat resistance in the moderate-temperature range
Compared with austenitic heat-resistant stainless steels and nickel-based superalloys, however, 13-8PH has:
Lower long-term high-temperature strength and creep resistance
Less suitability for continuous service at very high temperatures
It is therefore best regarded as a high-strength structural alloy with good moderate-temperature capability, rather than a primary choice for extreme high-temperature environments.
Summary
AMS 5629 (13-8PH) stainless steel provides reliable heat resistance for structural and mechanical components operating at moderate temperatures—typically up to about 600°F (≈315–320°C)—where it combines high strength, useful toughness and good oxidation performance; however, prolonged exposure above this range leads to overaging and property degradation, so it is not intended as a creep-resistant or very high-temperature alloy like specialised austenitic or nickel-based materials.
Machinability
Machinability of AMS 5629 (13-8PH) Stainless Steel
AMS 5629 (13-8PH) is a very high-strength precipitation-hardening martensitic stainless steel, so its machinability is moderate rather than easy. It machines best in the solution-treated or lower-strength aged conditions, with careful control of tooling, cutting data and cooling.
1. General Machining Behaviour
13-8PH is designed for high strength, so its base hardness is higher than that of 304/316.
It does not work harden as severely as austenitic grades, but cutting forces and tool wear are higher.
Machining should be planned as part of the overall solution treatment → aging → finishing route to minimise difficulty and achieve tight tolerances.
2. Preferred Condition for Machining
Rough machining is best done in the solution-treated (unaged) condition or in a relatively soft aging condition (e.g. higher aging temperatures).
After roughing, parts are normally aged to the specified condition (H950, H1000, H1050, etc.), then finish-machined or ground with light cuts.
Machining directly in the highest-strength conditions (e.g. H950) is possible but leads to short tool life, higher cutting forces and more heat.
3. Cutting Tools and Parameters
Carbide tooling is generally preferred for turning, milling and drilling.
Good practice includes:
Using insert grades designed for stainless / PH steels
Lower cutting speeds than for 304/316, with moderate to high feed to stay under any work-hardened skin
Positive rake and rigid setups to reduce chatter and edge chipping
Avoiding rubbing cuts and very light feeds that generate heat without removing material
Where tool steels or hardened materials are normally machined, similar tooling philosophy works well for 13-8PH.
4. Coolant Use and Chip Control
Generous use of cutting fluid or coolant is important to:
Remove heat from the cutting zone
Improve surface finish
Extend tool life
13-8PH can produce tough, continuous chips, especially in softer conditions, so:
Use chip breakers on inserts
Adjust feed and depth of cut to encourage chip breaking
Ensure safe chip evacuation in automatic or high-speed operations
Effective chip control reduces the risk of surface damage and machine downtime.
5. Drilling, Tapping and Threading
For drilling operations, use high-quality cobalt HSS or carbide drills with:
Moderate speeds
Steady feed
Pecking cycles for deep holes to clear chips
Tapping and threading need particular care because of the alloy’s strength:
Use strong, premium taps with good lubrication, or
Prefer thread milling for critical or high-strength conditions to reduce the risk of tap breakage
Apply appropriate thread tolerances, allowing for the material’s spring-back and high strength
Pre-drilling and chamfering help guide taps and reduce edge chipping.
6. Surface Finish, Distortion and Dimensional Control
13-8PH can achieve excellent surface finishes by turning, grinding and polishing, which is essential for:
Shafts and bearing seats
Landing gear pins and bush interfaces
Sealing and valve surfaces
To maintain dimensional accuracy:
Plan for rough machining → heat treatment → finish machining/grinding
Avoid overheating surfaces during machining or grinding to prevent local tempering or microcracking
Use light finishing passes with sharp tools after aging, especially on precision diameters and fits
Controlled machining sequences help keep distortion and residual stresses within acceptable limits.
Summary
The machinability of AMS 5629 (13-8PH) stainless steel is moderate for a very high-strength alloy: it machines best in the solution-treated or softer aged conditions using rigid setups, carbide tooling, conservative cutting speeds, generous coolant and careful drilling/tapping strategies, followed by light finishing or grinding after aging to deliver accurate, high-quality surfaces on critical aerospace and high-integrity mechanical components.
Corrosion Resistance
Corrosion Resistance of AMS 5629 (13-8PH) Stainless Steel
AMS 5629 (13-8PH) stainless steel offers good corrosion resistance for a high-strength precipitation-hardening martensitic alloy. It generally performs better than conventional martensitic stainless steels and is comparable to or slightly better than 17-4PH in many environments, while also providing very good resistance to stress-corrosion cracking when properly aged.
1. General Corrosion Behaviour
13-8PH provides a balanced combination of high mechanical strength and stainless corrosion resistance.
Its Cr–Ni–Mo–Al composition gives it:
Good resistance to uniform corrosion in many industrial, atmospheric and mildly marine environments
Better corrosion performance than standard martensitic grades such as 410 and 420
Corrosion resistance somewhat below the best austenitic grades (e.g. 316) in very aggressive chloride or acidic conditions
It is primarily intended for high-strength structural and mechanical service in mildly to moderately corrosive environments.
2. Atmospheric and Fresh-Water Environments
In atmospheric and fresh-water conditions, 13-8PH performs very well:
Good resistance to rusting and staining in rural, urban and light industrial atmospheres
Suitable for fresh water, cooling water and many process waters where chloride levels are moderate
Widely used for shafts, pins, fasteners and structural hardware exposed to weather, condensation and splash
Regular cleaning and sensible design to avoid stagnant pockets further improve long-term appearance and performance.
3. Marine and Chloride-Containing Environments
In marine and chloride-bearing environments, 13-8PH offers:
Better performance than carbon steel and conventional martensitic stainless steels
Useful resistance in marine atmospheres and splash zones for high-strength components
However, lower pitting and crevice corrosion resistance than molybdenum-rich austenitic or duplex stainless steels in hot, concentrated or stagnant chlorides
Continuous immersion in seawater, especially at elevated temperature or in stagnant conditions, is not ideal for the highest reliability applications; more highly alloyed stainless steels are preferred there.
4. Behaviour in Chemical Process Media
13-8PH is suitable for many mild to moderately corrosive chemical environments, including:
Lightly acidic or alkaline solutions at controlled concentrations and temperatures
Oils, fuels and many organic media
Some process plant environments where both high strength and stainless behaviour are needed
It is not recommended for:
Strong mineral acids or strong reducing acids
Hot, concentrated chloride solutions
Environments where maximum pitting, crevice or acid resistance is required and higher-alloyed stainless or nickel-base alloys are more appropriate
Actual medium composition, temperature and concentration should always be checked against available corrosion data for critical designs.
5. Stress-Corrosion Cracking and Hydrogen Effects
A key advantage of 13-8PH is its good resistance to stress-corrosion cracking (SCC) compared with many other high-strength steels:
Properly aged 13-8PH is less prone to chloride SCC than many conventional martensitic and some PH stainless steels
This makes it attractive for high-strength aerospace and process components operating in humid, chloride-bearing environments
Nevertheless, like other high-strength alloys, it can be sensitive to:
Hydrogen embrittlement from processes such as acid pickling, electroplating or excessive cathodic protection
High residual or applied tensile stresses in aggressive environments
Good practice includes controlling hydrogen-charging processes and minimising tensile stress where possible.
6. Influence of Heat Treatment and Aging Condition
Corrosion behaviour is closely linked to heat treatment and aging:
Solution treatment followed by the correct aging condition (H950, H1000, H1050, etc.) gives a refined microstructure and good corrosion resistance
Lower aging temperatures (higher strength) may be somewhat more susceptible to SCC and localized attack than higher-temperature aging with lower strength but improved toughness and environmental resistance
Over- or under-aging, or non-standard thermal histories, can alter microstructure and reduce both toughness and corrosion performance
For critical parts, the aging condition is chosen to give the best balance between strength, toughness, SCC resistance and general corrosion resistance.
7. Surface Condition and Design Considerations
As with all stainless steels, surface condition and design strongly affect corrosion performance:
Smooth, polished surfaces resist pitting and crevice formation better than rough or damaged surfaces
Thorough removal of scale, welding residues, embedded iron and machining contamination is essential
Good design practice avoids:
Tight crevices and water traps
Sharp corners and stagnant regions
Poor weld geometry or undercut where crevice corrosion can initiate
Well-finished welds, proper cleaning and sensible detailing greatly enhance service life in corrosive environments.
Summary
AMS 5629 (13-8PH) stainless steel provides good overall corrosion resistance and excellent stress-corrosion-cracking resistance for a very high-strength alloy: it outperforms conventional martensitic stainless steels and is comparable to or slightly better than 17-4PH in many environments, while remaining below highly alloyed austenitic and duplex grades for the most aggressive chloride or acid conditions, making it well suited for high-strength aerospace and industrial components in mildly to moderately corrosive service.
Heat Treatment
Heat Treatment of AMS 5629 (13-8PH) Stainless Steel
AMS 5629 (13-8PH) is a precipitation-hardening martensitic stainless steel whose final properties are controlled almost entirely by the heat treatment schedule. Correct solution treatment and aging are essential to achieve the specified combinations of strength, toughness and stress-corrosion cracking resistance.
1. Objectives of Heat Treatment
The main goals of heat treatment for AMS 5629 (13-8PH) are to:
Produce a uniform martensitic matrix by solution treatment and rapid cooling
Develop high strength and hardness through controlled precipitation (aging)
Optimise toughness and transverse properties, especially for aerospace structural parts
Minimise residual stresses and distortion introduced by forging, machining or welding
Heat treatment is always planned together with the chosen aging condition (H950, H1000, H1050, H1100, H1150, etc.) specified on the drawing or material standard.
2. Solution Treatment (Austenitizing)
Before aging, AMS 5629 material is solution treated to dissolve alloying elements into the austenite phase:
Material is heated into the austenitizing range (high temperature; exact value defined by the relevant specification or mill datasheet).
It is held long enough for uniform temperature and composition through the section.
The part is then rapidly cooled (typically air or oil, depending on size and specification) to form a mainly martensitic structure.
This solution-treated, unaged condition provides a consistent base for subsequent aging and gives relatively good machinability for roughing operations.
3. Aging / Precipitation Hardening Conditions
After solution treatment, AMS 5629 is aged to develop its final properties. Common aging conditions (examples only, exact times/temperatures must follow the standard or heat-treat spec) include:
Condition H950 – high strength, high hardness, lower toughness
Condition H1000 / H1025 / H1050 – slightly reduced strength with improved toughness and SCC resistance
Condition H1100 / H1150 – lower strength but maximum toughness and stress-corrosion performance
Aging is performed by:
Reheating to the specified aging temperature
Holding for the required time (commonly a few hours)
Cooling in air
During aging, fine intermetallic precipitates form in the martensitic matrix, significantly increasing yield and tensile strength and adjusting toughness and SCC behaviour.
4. Effect of Aging Temperature on Properties
The choice of aging temperature has a strong influence on mechanical and environmental performance:
Lower aging temperature (e.g. H950)
Maximum tensile and yield strength
Higher hardness
Lower but still useful toughness
Often used where strength and weight saving are critical
Intermediate aging (e.g. H1000–H1050)
Slightly reduced strength and hardness
Improved toughness and fatigue resistance
Good balance for many aerospace structural and landing gear parts
Higher aging temperature (e.g. H1100–H1150)
Further reduced strength
Maximum toughness and best stress-corrosion cracking resistance
Used where environmental resistance and damage tolerance are more important than peak strength
Selecting the correct condition is a design decision based on required strength–toughness–environment balance.
5. Stress Relief, Re-Aging and Repair Heat Treatment
In addition to the main hardening sequence, heat treatment may be used to manage stresses or repair parts:
Stress-relief treatments at sub-aging temperatures can reduce residual stresses from heavy machining or straightening without significantly changing strength.
For welded assemblies, a common approach is:
Solution treat the entire assembly (if design permits), then
Age to the required condition so that weld metal, HAZ and base metal all share a consistent microstructure and properties.
In some cases, parts may be re-solution treated and re-aged after significant repair welding or heavy re-work, provided geometry and tolerances allow.
All repair and re-heat-treat routes must respect the limits in the applicable material and component specifications.
6. Typical Production Heat Treatment Sequences
In practice, AMS 5629 components often follow sequences such as:
Forged parts / large sections
Forge / hot work
Solution treat
Rough machining
Age to specified condition (e.g. H1000, H1050)
Finish machining and grinding
Welded structures
Solution treat (or supplied solution-treated)
Weld in the solution-treated state with approved procedures
Re-solution treat if required by spec, or directly age
Age to final condition
Final machining / finishing
These sequences help maintain dimensional control, minimise distortion and ensure uniform properties.
7. Precautions During Heat Treatment
To obtain consistent, specification-compliant results, several precautions are important:
Avoid overheating during solution treatment, which can cause grain growth and reduce toughness.
Ensure uniform furnace loading and adequate soak time for thick sections.
Maintain accurate temperature control and calibration at solution and aging temperatures.
Use appropriate atmospheres or protective measures to limit oxidation and decarburisation, and allow machining allowance to remove any affected surface.
Do not exceed the maximum number of solution or aging cycles allowed by specification, as repeated thermal cycling can degrade properties.
Proper documentation of cycles and traceability is essential for aerospace and high-integrity components.
Summary
Heat treatment of AMS 5629 (13-8PH) stainless steel is based on solution treatment to form a martensitic structure followed by controlled aging (H950, H1000, H1050, H1100, H1150, etc.) to tune strength, toughness and stress-corrosion resistance; with carefully managed temperatures, times and sequences—often combined with stress relief or post-weld aging—the alloy can deliver highly consistent, high-strength properties for critical aerospace and industrial components.
Cold Working
Cold Working of AMS 5629 (13-8PH) Stainless Steel
AMS 5629 (13-8PH) is a high-strength precipitation-hardening martensitic stainless steel with limited ductility compared with austenitic grades. Cold working is possible, but it should generally be kept to light or moderate levels and always coordinated with the heat treatment and aging schedule.
1. General Cold Workability
13-8PH has lower ductility than 304/316, especially in high-strength aged conditions.
It can tolerate modest cold deformation for straightening, sizing and minor shape adjustment.
Heavy cold forming, sharp bending or deep drawing are not recommended, particularly on thicker sections or highly aged material.
2. Preferred Condition for Cold Working
Cold working should be carried out mainly in the solution-treated (unaged) condition or in a higher-temperature aged (softer) condition.
In these states, ductility is higher and the risk of cracking or excessive work hardening is reduced.
Cold working in the highest-strength aging conditions (such as H950) should be restricted to very small adjustments only.
3. Typical Cold Working Operations and Limits
Practical cold working operations include:
Straightening of bars, shafts and pins after heat treatment or machining.
Light bending with generous radii on plates, flats or bars in the solution-treated condition.
Cold sizing, swaging or light reduction of sections where total strain is limited.
Operations generally unsuitable for 13-8PH, except perhaps on very thin sections, include:
Severe cold heading with large upsets.
Tight-radius bending of thick sections.
Complex press-forming or deep drawing.
4. Effects on Mechanical Properties and Microstructure
Cold work increases local strength and hardness, and can reduce toughness and ductility in heavily strained regions.
Residual stresses from cold working can influence fatigue performance, dimensional stability and stress-corrosion behaviour.
Because 13-8PH already relies on a controlled precipitation-hardened martensitic structure, uncontrolled cold deformation can make properties less uniform through the section.
5. Stress Relief and Heat Treatment After Cold Work
After significant cold deformation, a stress-relief treatment or full re-heat-treatment sequence is often advisable.
For critical components, a typical approach is:
Cold work or straightening in the solution-treated condition → re-solution treatment (if allowed by spec) → aging to final condition.
For smaller adjustments after aging, a low-temperature stress-relief may help reduce residual stresses without substantially changing strength.
6. Design and Process Recommendations
Limit the amount of cold strain and avoid abrupt section changes or sharp corners in regions that must be cold worked.
Use larger bend radii and gradual transitions to reduce localised strain and risk of cracking.
Plan the manufacturing route so that major forming operations occur before final aging, with rough machining and cold work followed by solution treatment and aging, and then finish machining and grinding to size.
Summary
Cold working of AMS 5629 (13-8PH) should be restricted to light to moderate operations such as straightening, sizing and gentle bending in the solution-treated or softer aged conditions; heavier deformation can harm toughness and dimensional stability, so any significant cold work should be followed by appropriate stress relief or full solution treatment and aging to restore a uniform, reliable high-strength microstructure for critical components.
