Custom 455 (also written Alloy 455) is a precipitation-hardening martensitic stainless steel registered as UNS S45500 and specified primarily under AMS 5617. It sits in the same broad PH stainless category as 17-4PH and 15-5PH, but its hardening mechanism relies on a different set of precipitates: rather than copper alone, Custom 455 combines roughly 1.5-2.5% copper with 0.80-1.40% titanium (plus a small niobium/tantalum addition) to form fine intermetallic precipitates during a single-stage aging treatment. That gives Custom 455 a distinctively high strength-to-toughness ratio — yield strengths above 1650 MPa (240 ksi) are achievable in the H900 condition while still retaining useful ductility and impact toughness.

Like other PH stainless grades, Custom 455 is supplied and machined in the solution-annealed condition (roughly 30-35 HRC, relatively soft and machinable) and aged afterward to reach its final mechanical properties. Its combination of high strength, good corrosion resistance, and weldability makes it a common choice for aerospace structural fittings, high-strength fasteners, landing gear components, surgical instruments, and springs where 17-4PH's strength ceiling isn't quite enough.

Note: this page's prior content omitted the copper and titanium content entirely — the two elements that actually drive Custom 455's precipitation-hardening response. Both have been added here per AMS 5617 / UNS S45500.

In the solution-annealed condition, Custom 455 machines comparably to 17-4PH — moderate work hardening, low thermal conductivity that keeps heat at the cutting edge, and a chip that stays manageable with sharp, positive-rake tooling and steady feed. The titanium-bearing intermetallics that give this alloy its strength after aging are not yet precipitated in the annealed state, so cutting forces in that condition are relatively modest for a stainless steel of this ultimate strength class.

The gap opens up after aging. Once Custom 455 is heat treated to H900 or H950, it reaches noticeably higher hardness and tensile strength than aged 17-4PH, and tool wear rises accordingly. As with other PH stainless grades, the standard approach is to complete the bulk of roughing and semi-finishing in the annealed condition, hold final critical dimensions for after aging where distortion allowances permit, and expect reduced speeds, more rigid setups, and closer tool-wear monitoring for any machining done post-age.

Figures assume the solution-annealed condition. Reduce speeds once the part is aged to H900-H1050.

Turning

Parting / Grooving

Milling