Uns C72900 C729 -

| Process | Guidelines | |---------|------------| | | Best performed in the annealed condition. Cold working beyond 20 % strain may cause cracking in the hardened states. | | Welding | Pre‑heat not required for thickness ≤ 12 mm. Recommended filler metals: ER308L , ER309L , ER316L for corrosion‑critical zones, or EPRI‑17‑4 filler for matching alloy. Post‑weld heat treat (solution anneal + aging) restores strength. | | Machining | Good machinability in annealed state; H900 is tougher and may require carbide tooling, low feed, high rpm, and ample coolant. Typical cutting speeds: 60–90 m/min (HSS) → 150–200 m/min (carbide). | | Heat‑treatment after machining | If final dimensions are critical, perform solution anneal → water quench → age after machining to avoid distortion. | | Surface finish | Polished to < 0.2 µm Ra for critical corrosion zones; standard 120‑grit (Ra ≈ 2 µm) is adequate for most mechanical parts. |

C72900 is engineered for extreme reliability under severe loading and environmental conditions. ToughMet® Nickel Bronze 729 / C729 / C72900

UNS C72900, commonly known as or 17‑4 PH (precipitation‑hardening), is a martensitic‑type stainless steel that combines high strength, good corrosion resistance, and excellent heat‑treatability. It is widely used in aerospace, chemical processing, petrochemical, medical, and high‑performance engineering applications where a balance of mechanical performance and corrosion resistance is required. uns c72900 c729

Notes:

| Environment | Performance | Comments | |-------------|-------------|----------| | | Comparable to 304/316; excellent | Forms a protective Cr₂O₃ layer | | Mild seawater | Good, but not as high as 316L | Cu content can cause slight galvanic activity; still acceptable up to 5 % NaCl | | Pitting/Crevice (chloride) | Moderate–good; pitting potential (Eₚ) ≈ +0.30 V (SCE) | Better when aged to H1025 or H1075; H900 may be slightly more susceptible due to higher tensile stress | | Oxidizing acids (H₂SO₄, HNO₃) | Excellent | Passivation similar to 304 | | Reducing acids (HCl, H₂S) | Poorer than 316; not recommended for high‑concentration HCl | Use only where concentration < 10 % and temperature < 50 °C | | High‑temperature oxidation | Stable up to 600 °C (1112 °F) for short periods | Above 600 °C, Cr‑oxide scale may spall | | Stress‑corrosion cracking (SCC) | Generally good; resistant to SCC in chlorides when aged to H1025/H1075 | H900 can be susceptible under high tensile stress in chloride environments | | Process | Guidelines | |---------|------------| | |

| Condition | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation % (A) | Hardness | |-----------|------------------------|----------------------|------------------|----------| | | 620 MPa | 415 MPa | 30 % | 70 HRB | | H900 | 1380 MPa | 1240 MPa | 10 % | 44‑48 HRC | | H1025 | 1150 MPa | 1060 MPa | 12‑14 % | 38‑42 HRC | | H1075 | 950 MPa | 800 MPa | 15‑18 % | 34‑38 HRC | | DAH | 1300 MPa | 1150 MPa | 11 % | 42‑45 HRC | | Impact (Charpy V‑Notch, 0 °C) | — | — | — | 60‑80 J (H1025) | | Modulus of Elasticity | ≈ 200 GPa (29 Msi) | — | — | — | | Density | 7.75 g cm⁻³ (0.28 lb in⁻³) | — | — | — |

Not recommended for strong oxidizing acids (e.g., nitric) or ammonia-rich environments. Recommended filler metals: ER308L , ER309L , ER316L

C72900 exhibits spinodal hardening – a unique decomposition of the Cu-Ni-Sn solid solution during aging, producing a coherent, nano-scale modulated structure that resists softening up to ~400°C.