ASTM B408
ASTM B408 is the ASTM International standard specification for Incoloy 800 (UNS N08800) and Incoloy 800H (UNS N08810) nickel-iron-chromium alloy rod and bar. The specification covers material in the annealed condition in diameters from 0.188 inch to 8.000 inches, setting requirements for chemical composition (nominal 32% Ni, 21% Cr, balance Fe), mechanical properties, grain size, and test methods for this high-temperature alloy. Incoloy 800 bar to ASTM B408 is the standard commercial-grade form used for machined components in high-temperature process equipment, heat exchangers, furnace hardware, and structural aerospace fittings operating in oxidizing or mildly reducing atmospheres up to 1500°F (816°C).
ASTM B408 covers three distinct variants: UNS N08800 (standard Incoloy 800), UNS N08810 (Incoloy 800H, higher carbon for improved creep resistance), and UNS N08811 (Incoloy 800HT, with titanium and aluminum additions for maximum elevated-temperature properties). Each variant has distinct composition and grain size requirements within the B408 specification.
ASTM B408 Incoloy 800 bar in the annealed condition meets minimum 75,000 psi UTS with minimum 30% elongation. The alloy maintains useful strength to 1500°F and creep resistance to 1200°F (649°C); for applications above 1200°F requiring creep strength, Incoloy 800H or 800HT with their coarser grain size (ASTM 5 or coarser) and higher creep resistance are specified. The austenitic FCC crystal structure of Incoloy 800 provides good ductility and toughness over a wide temperature range including sub-zero temperatures encountered in cryogenic applications.
Applications of ASTM B408
- Industrial furnace heating element supports and shields
- Steam superheater and reheater tube supports
- Heat exchanger channel and header machined components
- Gas turbine exhaust system structural fittings
- Chemical process reactor internal components
- Nuclear steam generator structural members
ASTM B409 — Incoloy 800 Plate
Incoloy 800 plate, sheet, and strip for fabricated high-temperature pressure vessel and heat exchanger components.
AMS 5873 — Incoloy 825 Bar
Incoloy 825 Ni-Fe-Cr-Mo-Cu alloy for corrosion resistance in both oxidizing and reducing acid environments.
Certified Material for Critical Service
ASTM B408 certifications include chemical composition per heat (all elements in the specification table), mechanical properties per lot (tensile, yield, elongation), grain size per heat for Incoloy 800H and 800HT (ASTM 5 or coarser required for H and HT), and solution anneal condition documentation. Mill certifications must explicitly state the UNS designation (N08800, N08810, or N08811) as the three variants have different properties and are not interchangeable in design applications.