Incoloy 800H Alloy | N08810 | 1.4958 | High-Temp Creep Resistant | Fushun Metal

Incoloy 800H / N08810 / 1.4958 — Introduction

Incoloy 800H, designated UNS N08810 and EN 1.4958, is the controlled high-carbon variant of the Incoloy 800 family—an iron-nickel-chromium austenitic alloy engineered for sustained high-temperature structural service where creep and rupture strength govern design life. The defining “H” designation derives from a deliberately elevated carbon range of 0.05–0.10% (compared with ≤0.10% for standard 800), which, when combined with a high-temperature solution anneal at 1120–1170°C, produces an intentionally coarse-grained microstructure (ASTM 5 or coarser). This coarse grain structure dramatically improves creep-rupture strength and stress-rupture ductility in the 600–870°C range by suppressing grain-boundary sliding—the dominant deformation mechanism in long-term, low-stress elevated-temperature service. With 19–23% chromium and 30–35% nickel, the alloy also provides excellent resistance to oxidation, carburization, and nitriding in combustion and process-gas atmospheres, making it the industry-standard material for ethylene cracking furnace tubes, steam-hydrocarbon reformer pigtails, and nuclear steam generator tubing.

At Fushun Metal, Incoloy 800H is manufactured through a fully integrated triple-melt route under one roof. VIM primary melting under high vacuum ensures precise control of the narrow carbon window (0.05–0.10%) and the Al+Ti balance (target 0.85–1.20%) that governs both precipitation strengthening and oxidation resistance at temperature. The VIM electrode passes to VAR, where controlled directional solidification eliminates macro-segregation and yields chemically homogeneous electrode stock with uniform Al and Ti distribution—essential for consistent precipitation kinetics across large-section products. For mission-critical petrochemical furnace and nuclear steam generator applications, we deploy PESR as the final stage, achieving deep desulfurization and oxide refinement through argon-shielded reactive slag chemistry for maximum creep ductility and microstructural cleanliness.

Every heat is processed, solution-annealed, quenched, and tested within Fushun Metal’s certified quality management system—ISO 9001 for manufacturing process control and AS9120B for aerospace distribution traceability. Full digital traceability links each production lot from melt heat number through remelt sequence, hot-working reduction ratio, and final solution-annealing batch. Grain size verification per ASTM E112, room-temperature and elevated-temperature tensile testing, and creep-rupture testing per ASTM E139 are standard quality assurance deliverables. Mill test certificates to EN 10204 3.1 or 3.2 accompany every shipment.

Equivalent Grades of Incoloy 800H Across International Standards

Incoloy 800H is codified under multiple national and international specification systems. The table below maps its designations and governing standards across major markets. Fushun Metal certifies to all listed specifications and can dual-certify heats where required.

Applications of Incoloy 800H

Incoloy 800H is the default specification for long-term, load-bearing equipment operating in the 600–870°C range in oxidizing, carburizing, or nitriding atmospheres. Its combination of creep strength from controlled coarse-grain structure and surface stability from 19–23% chromium makes it uniquely suited to petrochemical furnace and nuclear steam generator service where design lives extend to 100,000 hours or more.

Incoloy 800H — Supply Range by Fushun Metal

Fushun Metal stocks and processes Incoloy 800H across all major mill forms from a single integrated facility. Our in-house 6000-ton hydraulic open-die press, 1800-ton precision radial forger (GFM), and multi-stand 850/550/350/250 rolling mills enable a broad dimensional envelope without outsourcing—ensuring uninterrupted lot traceability from melt to delivery under ISO 9001 and AS9120B. All material is supplied in the solution-annealed condition per ASTM B407 / B408 / B409 at 1120–1170°C (H-grade specific), producing the coarse ASTM 5+ grain structure required for maximum creep-rupture life. Grain size certification per ASTM E112 is standard. Room-temperature tensile and elevated-temperature creep-rupture testing per ASTM E139 are performed on each heat as applicable. Mill test certificates to EN 10204 3.1 or 3.2 accompany every shipment. Welding consumable: ERNiCr-3 (Inconel 82) or ERNiCrCoMo-1 filler; ENiCrFe-3 electrode.

Chemical Composition of Incoloy 800H — ASTM B407 / ASTM B409

All heats produced by Fushun Metal are melted via VIM+VAR or VIM+PESR and verified against the composition limits below by optical emission spectrometry and LECO combustion analysis. Full chemical certificates are issued with every shipment under ISO 9001 and AS9120B quality management. The carbon range of 0.05–0.10% is the defining H-grade characteristic—sufficient carbon is present to form a controlled distribution of M₂₃C₆ carbides at grain boundaries during high-temperature service, pinning grain boundaries against sliding and dramatically enhancing creep strength without embrittling the matrix. The combined Al+Ti content (typically 0.85–1.20%) also contributes a minor gamma-prime precipitation-strengthening component.

Mechanical Properties of Incoloy 800H — Per Product Form

Incoloy 800H derives its high-temperature creep strength from the coarse-grain austenitic microstructure produced by solution annealing at 1120–1170°C followed by rapid cooling. The elevated carbon content (0.05–0.10%) provides grain-boundary carbide pinning during service. Room-temperature values below represent minimum guarantees per ASTM B407, B408, and B409 in the solution-annealed condition. Elevated-temperature tensile and creep-rupture data are provided as typical values for design reference—exact values depend on grain size, section thickness, and specific heat treatment parameters.

Fushun Metal performs all solution annealing in-house under calibrated furnace controls. The H-grade annealing temperature range (1120–1170°C) is deliberately higher than that of standard Incoloy 800 to promote controlled grain growth to ASTM 5 or coarser. Rapid water quenching follows to suppress unwanted carbide precipitation during cooling. The 800H alloy is readily weldable using ERNiCr-3 (Inconel 82) or ERNiCrCoMo-1 filler metal with standard GTAW or SMAW procedures; post-weld solution annealing is not typically required for service at design temperatures below 600°C where as-welded ductility is adequate.

Physical constants: Density 7.94–8.0 g/cm³; Melting range 1350–1400°C; Hardness ≤200 HB / ≤90 HRB (annealed); Modulus of elasticity 200 GPa at 20°C; Thermal conductivity ~15 W/m·K at 100°C; Coefficient of thermal expansion 14.0–14.4 μm/m·°C (20–100°C). Continuous maximum service temperature in air: 815°C; short-term excursions to 980°C permissible. The alloy is non-magnetic due to its fully austenitic structure.