Material Family

Nickel-Iron-Chromium Austenitic Alloy (High-Temperature Optimized)

Premium bar grades for high-temperature, load-bearing applications.

Primary Distinction

Guaranteed Enhanced Creep Rupture Strength at temperatures above 540°C (1000°F).

This is the primary reason to specify 800H/HT over standard 800 bar for high-temperature designs.

Common Forms (Bar)

Hot Rolled, Forged Rounds, Squares, or as Forging Billet. Also available in other sections.

Often supplied as forging billet for critical components like turbine parts or as bar for machining fixtures.

Chemical Composition (Typical wt.%)

Common: Ni 30.0-35.0, Cr 19.0-23.0, Fe ≥39.5
C: 0.05 - 0.10
Al: 0.15 - 0.60
Ti: 0.15 - 0.60
800HT Specific: (Al + Ti) must be 0.85 - 1.20

Controlled Carbon (C) is key for strength. 800HT's required (Al+Ti) sum ensures optimal precipitation strengthening for the best creep performance.

Mechanical Properties (Annealed, Room Temp)

Tensile Strength (Rm): 450 - 600 MPa (min yield varies by spec)
Yield Strength (Rp0.2): 170 - 240 MPa (min)
Elongation (A): 30% min

Room temperature properties are similar to standard 800. The critical properties are elevated temperature strength and creep data.

Physical Properties

Density: 7.94 g/cm³
Melting Range: 1350 - 1400 °C
Primary Service Range: 600°C - 950°C (1110°F - 1740°F) for maximum benefit of enhanced creep strength.

Optimized for long-term exposure in this high-temperature window.

Mandatory Thermal-Mechanical Processing

Bar must be annealed at a minimum of 1121°C (2050°F) to achieve an ASTM grain size of 5 or coarser (typically ASTM 3-5). This is a non-negotiable requirement per ASTM B407.

This controlled coarse grain structure is essential to develop the specified high-temperature creep strength. It is verified via metallographic examination.

Key Standards (Bar)

ASTM B408 / ASME SB-408 (Rod and Bar)
MANDATORY Supplementary Spec: ASTM B407 (Covers grain size and heat treatment requirements for UNS N08810 & N08811)

Purchasing to ASTM B408 alone is insufficient. Orders must specify compliance with ASTM B407 to guarantee the high-temperature properties.

Machinability

Machinability Rating: ~40%. Similar to standard 800 but can be slightly tougher due to the coarse grain structure. Requires sharp tools and positive rakes.

All machining is performed on the as-supplied annealed bar. The coarse grain structure is not detrimental to machining.

Typical Bar Applications

• Petrochemical: Forgings and machined parts for reformer furnace hangers, pigtails, tube supports, outlet headers.
• Power Generation: Turbine blades, bolts, fasteners, valve components for high-temperature steam service.
• Industrial Furnaces: Machined fixtures, trays, baskets, rollers for heat treating and sintering.
• Heat Exchangers: Header bars, support strips for high-temperature units.

The dominant bar material for high-temperature, load-bearing components in the petrochemical and power industries.