PH 13-8MO Stainless Steel

PH 13-8 Mo is specified wherever high strength, fracture toughness and corrosion resistance must be achieved within a single material. Typical applications include aircraft structural fittings, aerospace fasteners in safety-critical assemblies, landing gear components, helicopter rotor hubs and rotating structural parts, petrochemical valves and fittings operating under sustained load, and structural applications across the defence sector.

PH 13-8 Mo delivers tensile strength up to 1517 MPa in the H950 condition — among the highest available in any wrought stainless steel. Six precipitation hardening conditions (H950 through H1150) allow engineers to select the precise balance of strength and ductility their application demands. Minimum elongation of 10% is maintained even at H950, confirming genuine toughness at maximum strength. Mechanical properties are tested and certified in both longitudinal and transverse orientations per AMS 5629, and the alloy retains its characteristics from cryogenic temperatures through to 316°C (600°F) in service.

Stress corrosion cracking resistance is one of the defining characteristics of PH 13-8 Mo, and a primary reason it is specified over other precipitation hardening grades in aggressive environments. The combination of chromium, nickel and molybdenum within the composition forms a stable passive layer that performs reliably under simultaneous mechanical loading and corrosive exposure. The alloy is well suited to marine, coastal aerospace and chemical processing environments, and to applications where chloride-induced pitting is a concern.

Both AMS 5629 and AMS 5864 mandate production via Vacuum Induction Melting followed by Vacuum Arc Remelting. This dual-melt process eliminates non-metallic inclusions and ensures consistent chemistry across the full cross-section of every bar, plate and forging. It is a specification requirement — not an enhancement — and it underpins the fracture toughness and transverse mechanical properties that make PH 13-8 Mo suitable for the most demanding structural applications. Every heat undergoes macrostructure examination, chemical analysis and tensile property testing prior to certification.

PH 13-8 Mo should be machined in the solution annealed condition, before final age hardening to the required H-condition. In this state the material behaves more predictably than austenitic stainless steels, with a lower work hardening rate that makes toolpath planning more straightforward. Dimensional change during ageing is minimal, meaning complex geometries can be machined to near-final dimensions before heat treatment without significant distortion risk. Where welding is required, this should be carried out in the solution annealed condition; for critical joints, re-solution treatment and re-ageing after welding is recommended. Applicable ageing conditions and temperatures are defined within AMS 5629 and AMS 5864.

Dynamic Metals supplies PH 13-8 Mo to AMS 5629 as bar, wire and forgings, and to AMS 5864 as plate up to 3 inches (76.2 mm) nominal thickness. All material is supplied in the solution heat-treated condition, ready for customer age hardening to the required H-condition. No minimum order quantities apply on stock items, making us equally suited to prototype development programmes and full production contracts.

PH 13-8 Mo occupies a unique position within the stainless steel family — delivering tensile strength levels that rival specialist alloy steels, while retaining the corrosion resistance expected of a stainless grade. The selectable ageing system means a single stock material can be processed to meet a range of application requirements. Consistent transverse mechanical properties — a direct result of the VIM/VAR melting process — make it suitable for components loaded across multiple axes, which eliminates many other high-strength steels from consideration. Machinability in the annealed condition, combined with minimal distortion during ageing, gives manufacturers a practical and reliable processing route even for complex, tight-tolerance parts.

Dynamic Metals has supplied PH 13-8 Mo to aerospace and defence customers since 1997. We hold certified stock to both AMS 5629 and AMS 5864, supplied with full material certification and traceability to the original VIM/VAR melt heat. Our team can advise on ageing conditions, processing routes and specification requirements — and with no minimum order quantities, we can support both development programmes and production contracts alike. AS9100 certified. Fast UK delivery on standard stock sizes.