Precipitation Hardened Stainless Steel Pipe and Tube

Precipitation Hardening Stainless Steel Tube is a special steel pipe that achieves a balance between high strength, high toughness, and corrosion resistance by precipitating intermetallic compounds through heat treatment. Its core value lies in obtaining ultra-high strength without cold processing, while maintaining the corrosion resistance gene of austenitic stainless steel. It is a key material for aerospace, nuclear energy, and precision instruments.

Performance advantages and mechanisms

|* * Characteristics * * | Numerical/Performance | * * Implementation Principle * *|

|Ultra high strength | Tensile strength after aging ≥ 1500 MPa (such as 17-4PH) | Cu/NiAl/Ti precipitates nanoscale strengthening phases (ε - Cu, Ni ∝ Ti)|

|Corrosion resistance | Neutral salt spray test>500h (better than 304 stainless steel) | Cr content ≥ 15% forms passive film+Mo/Cu auxiliary protection|

|Process adaptability | Solid solution state machinable, directly used after aging | Martensitic/Semi austenitic matrix+low-temperature aging strengthening|

|Dimensional stability | Heat treatment deformation<0.05% | Low temperature aging (480 ° C ± 10 ° C) to avoid phase transition stress|

Note: The strength can reach three times that of ordinary 304 stainless steel, while avoiding the welding brittleness problem of martensitic stainless steel.

Three major alloy systems and representative grades

1. Martensitic precipitation hardening steel (dominated by high strength)

- 17-4PH (S17400)： 

-Composition: Cr 16%/Ni 4%/Cu 4%

-Aging process: H900 (480 ° C × 1h) → Strength increased to 1310 MPa

-*Application: Nuclear power valve stem, aviation hydraulic pipe

2. Semi austenitic body type (high toughness+weldable)

- 17-7PH (S17700)： 

-Composition * *: Cr 17%/Ni 7%/Al 1.2%

-Process * *: RH950 (955 ° C solid solution+cold treatment+510 ° C aging)

-*Feature * *: Direct aging after welding, used for thin-walled sensor tubes

3. Austenitic type (corrosion resistance priority)

- A-286 (S66286)： 

-Composition: Fe-25Ni-15Cr-2Ti-1Mo (belonging to iron nickel based)

-Strength: Yield strength after aging ≥ 800 MPa (maintained at 550 MPa at 704 ° C)

-Scenario * *: High temperature fuel tube for rocket engine.

Heat treatment process determines performance

Key four steps:

1.  Solid solution treatment * * (1020-1100 ° C water quenching):

-Dissolve and separate phases → obtain supersaturated solid solution (hardness ≤ 32 HRC, easy to machine)

2. Adjustment treatment * * (only required for semi austenitic body types):

-17-7PH is kept at 760 ° C for 90 minutes to promote carbide precipitation and increase the Ms point (martensitic transformation temperature)

3. Cryogenic treatment(-73 ° C × 8h):

-Drive austenite → martensite transformation (a necessary step for semi austenitic steel)

4. Age hardening (480-620 ° C × 1-4 hours):

-Precipitation of nanoscale strengthening phase (such as 17-4PH precipitation of ε - Cu particles with a diameter of 3-10nm)

>Warning: A temperature deviation of ± 15 ° C during aging will result in a strength fluctuation of ± 10%! Accurate temperature control is required.

Adaptability to corrosion scenarios

|Corrosion Types | PH Stainless Steel Countermeasures | Failure Case Avoidance|

|Stress Corrosion Cracking | Control Ni Content ≥ 4% (17-4PH) | 304 Stainless Steel Bolt in a Chemical Plant Breaks Half a Year → Replace 17-4PH, Life>5 Years|

|* * Pitting corrosion * * | Adding Mo (such as Custom 450 containing Mo 0.5%) | After upgrading the seawater pipeline, the pitting corrosion rate is ↓ 80%|

|Hydrogen embrittlement * * | Limiting hardness ≤ 33 HRC (nuclear power standard ASME III) | Adopting H1150 state (aging temperature 620 ° C)|

Manufacturing process difficulties

1. Seamless pipe forming:

-Hot extrusion (1150 ° C) → cold rolling → solution treatment to ensure a wall thickness tolerance of ± 0.05mm (medical grade requirement)

2.Welding Control:

-Select ultra-low carbon welding wire (ER630) with interlayer temperature<100 ° C to prevent sensitization

3. Surface Treatment:

-Electrolytic polishing (Ra ≤ 0.1 μ m) reduces the starting point of corrosion and is used for semiconductor gas delivery pipes

6、 Application scenarios and selection logic

|* * Domain * * | * * Component Case * * | * * Brand Selection * * | * * Core Requirements * *|

|Aerospace hydraulic actuator | 15-5PH (15% higher toughness than 17-4PH) | Anti vibration fatigue+5000psi high-pressure seal|

|Nuclear Power | Control Rod Drive Mechanism Sleeve | 17-4PH H1100 | Resistance to Neutron Radiation+350 ° C Creep Resistance|

|Medical equipment | Surgical robot precision shaft tube | 17-7PH RH950 | Non magnetic+zero corrosion in body fluid environment|

|Energy and Chemical Industry | Supercritical CO ₂ Extraction Device Tube | Custom 450 | Resistant to 200 ° C/30MPa Acidic Medium|

Technological frontiers

1. Additive Manufacturing:

-Laser powder bed melting (LPBF) forming 17-4PH pipe fittings, with a tensile strength exceeding 1450 MPa (density>99.5%)

2. Intelligent Heat Treatment:

-Electromagnetic induction aging technology accurately controls temperature by ± 3 ° C, reducing energy consumption by 40%

3. Corrosion prediction model:

-Machine learning analysis of Cl ⁻/pH/stress three factors to predict the service life of 17-4PH pipes (error<10%)

Steel selection rules

>- Choose martensitic type for strength (17-4PH) : suitable for high stress structural components;

>- Choose a semi austenitic shape (17-7PH) for formability: Suitable for complex bent pipes;

>- Choose austenitic type (A-286) for high temperature corrosion resistance: Suitable for environments above 600 ° C.

Failure Warning

A satellite support tube experienced stress fracture in orbit due to the use of solid solution 17-4PH that was not aged. * * Precipitation hardening steel without heat treatment is equivalent to performance scrap