Inconel 800H
Introduction to Inconel 800H
Inconel 800H is a high-performance variation of the Inconel 800 series, engineered for enhanced high-temperature mechanical properties. It maintains the core chemical composition of Inconel 800—nickel, iron, and chromium—but is modified with controlled carbon (0.05–0.10%) and aluminum + titanium content to improve creep-rupture strength and structural integrity during long-term exposure at 650–1000°C.
This alloy excels in thermal stress environments such as hydrocarbon reformers, heat exchangers, and power boiler tubing. Its increased grain size and stress relaxation properties make it suitable for pressure-bound components operating under cyclic thermal loads. CNC machining is typically applied after solution annealing and stabilization to ensure precision and mechanical reliability.
Chemical, Physical, and Mechanical Properties of Inconel 800H
Inconel 800H (UNS N08810 / ASTM B409 / ASME SB409 / DIN 1.4958) is supplied in solution-annealed condition and used in code-stamped pressure applications requiring elevated temperature performance.
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Nickel (Ni) | 30.0–35.0 | Base metal providing oxidation and carburization resistance |
Chromium (Cr) | 19.0–23.0 | Promotes stable oxide formation for high-temperature protection |
Iron (Fe) | Balance (≥39.5%) | Enhances structural matrix and strength |
Carbon (C) | 0.05–0.10 | Increases creep and rupture resistance |
Manganese (Mn) | ≤1.5 | Supports hot workability |
Silicon (Si) | ≤1.0 | Enhances oxidation behavior |
Aluminum (Al) | 0.15–0.60 | γ′ formation and oxidation resistance |
Titanium (Ti) | 0.15–0.60 | Stabilizes the microstructure |
Sulfur (S) | ≤0.015 | Minimized for improved weldability |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 7.94 g/cm³ | ASTM B311 |
Melting Range | 1357–1385°C | ASTM E1268 |
Thermal Conductivity | 11.2 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 1.18 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 14.4 µm/m·°C (20–1000°C) | ASTM E228 |
Specific Heat Capacity | 460 J/kg·K at 20°C | ASTM E1269 |
Elastic Modulus | 190 GPa at 20°C | ASTM E111 |
Mechanical Properties (Solution Annealed Condition)
Property | Value (Typical) | Test Standard |
|---|---|---|
Tensile Strength | 520–620 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 210–310 MPa | ASTM E8/E8M |
Elongation | ≥30% (25mm gauge) | ASTM E8/E8M |
Hardness | 150–180 HB | ASTM E10 |
Creep Rupture Strength | ≥95 MPa @ 815°C, 1000h | ASTM E139 |
Key Characteristics of Inconel 800H
High Creep-Rupture Strength: Carbon level (0.05–0.10%) ensures superior resistance to long-term thermal deformation and rupture at ≥800°C.
Thermal Stability: Retains metallurgical integrity during stress relaxation in cyclic or base-load thermal environments.
Superior Weldability: Titanium and aluminum additions reduce the risk of sensitization and grain boundary attack during joining.
CNC Machinability: Machined in solution-annealed condition to achieve dimensional tolerance of ±0.01 mm and surface finish Ra ≤ 0.8 µm.
CNC Machining Challenges and Solutions for Inconel 800H
Machining Challenges
Work Hardening Tendency
The high nickel and iron content increase the strain hardening exponent, requiring consistent depth of cut to prevent tool chatter and BUE.
Tool Wear at Elevated Cutting Temperatures
Local heat accumulation at the tool-workpiece interface accelerates flank and crater wear, especially in interrupted cuts.
Sulfur-Free Tooling Environment
Due to the alloy's sensitivity to sulfur, cutting fluids must be carefully selected to prevent surface embrittlement or chemical attack.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | Carbide tools with PVD coatings (TiAlN, AlCrN) | Excellent hot hardness and oxidation resistance |
Coating | 3–5 µm TiAlN or AlTiN | Reduces friction and prevents built-up edge |
Geometry | Positive rake angle (10–12°) with honed edges | Promotes chip flow and lowers cutting resistance |
Cutting Parameters (ISO 3685)
Operation | Speed (m/min) | Feed (mm/rev) | DOC (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 30–50 | 0.20–0.30 | 2.0–3.0 | 80–100 |
Finishing | 60–90 | 0.05–0.10 | 0.3–0.8 | 100–150 |
Surface Treatment for Machined Inconel 800H Parts
Hot Isostatic Pressing (HIP)
HIP improves structural density and creep strength by eliminating porosity in cast or fabricated parts, critical for long-term pressure vessel performance.
Heat Treatment
Heat Treatment includes solution annealing at 1100–1150°C followed by rapid air cooling to stabilize grain size and optimize creep performance.
Superalloy Welding
Superalloy Welding uses low-heat-input GTAW with matching filler metals to minimize hot cracking and intergranular corrosion.
Thermal Barrier Coating (TBC)
TBC Coating applies 125–250 µm of YSZ to resist radiative heat and extend component lifespan in reformer and furnace environments.
Electrical Discharge Machining (EDM)
EDM allows for the creation of fine slots, grooves, and tight-tolerance features with an accuracy of up to ±0.01 mm.
Deep Hole Drilling
Deep Hole Drilling enables the creation of precise L/D > 40:1 flow channels in the heat exchanger and reformer components.
Material Testing and Analysis
Material Testing includes grain size analysis (ASTM E112), tensile/corrosion testing, and non-destructive examination per ASME standards.
Industry Applications of Inconel 800H Components
Petrochemical Furnaces
Reformer outlet headers, ethylene cracking tubes, and manifold systems.
Maintains creep strength and corrosion resistance at 800–1000°C in mixed gas environments.
Power Generation (Boiler Systems)
Superheater/reheater tubing, waterwall headers, and pressure boundaries.
Long service life under creep and thermal fatigue conditions.
Nuclear Steam Generators
Core support structures, fuel cladding, and secondary loop piping.
Excellent stress corrosion cracking resistance in chloride-rich and radiative conditions.
Heat-Treating Equipment
Fixtures, muffles, baskets, and trays.
Resists carburization, scaling, and dimensional drift during repeated cycling.
FAQs
What advantages does Inconel 800H offer over Inconel 800 in creep resistance?
How can machining-induced work hardening in Inconel 800H be minimized?
Is Inconel 800H suitable for pressure vessel applications in petrochemical plants?
What quality control steps does Neway use for Inconel 800H CNC and welded parts?
Can Neway deliver HIP-treated and heat-stabilized Inconel 800H components?
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