Hastelloy C-4
Introduction to Hastelloy C-4
Hastelloy C-4 is a nickel-chromium-molybdenum alloy developed for exceptional resistance to strong oxidizing and reducing agents, especially in high-temperature environments. Its standout feature is its outstanding stability against grain boundary precipitation in the heat-affected zone (HAZ), making it particularly suitable for welding and thermal cycling operations.
Engineered to resist stress corrosion cracking, pitting, and crevice corrosion in oxidizing and acidic media, Hastelloy C-4 is widely CNC machined into components for chemical reactors, heat exchangers, scrubber systems, and flue gas desulfurization units. The alloy maintains mechanical strength and corrosion resistance at service temperatures up to 1040°C, making it ideal for aggressive chemical processing environments.
Chemical, Physical, and Mechanical Properties of Hastelloy C-4
Hastelloy C-4 (UNS N06455 / ASTM B575 / B564 / B619) is a corrosion-resistant alloy that maintains structural integrity under prolonged thermal exposure. Its low carbon, silicon, and iron contents prevent carbide and other phase formation during welding and heat treatment.
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Nickel (Ni) | Balance (≥65.0) | Base element; enhances corrosion resistance and thermal stability |
Chromium (Cr) | 14.5–16.5 | Provides resistance to oxidizing agents and forms passive oxide films |
Molybdenum (Mo) | 14.0–17.0 | Increases resistance to reducing environments and localized corrosion |
Iron (Fe) | ≤3.0 | Minimizes phase instability |
Cobalt (Co) | ≤2.0 | Limited as an impurity |
Carbon (C) | ≤0.01 | Prevents carbide precipitation in the heat-affected zone |
Manganese (Mn) | ≤1.0 | Improves hot workability |
Silicon (Si) | ≤0.08 | Low to avoid intergranular corrosion |
Phosphorus (P) | ≤0.025 | Controlled for weldability |
Sulfur (S) | ≤0.010 | Prevents hot cracking during machining |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 8.64 g/cm³ | ASTM B311 |
Melting Range | 1325–1370°C | ASTM E1268 |
Thermal Conductivity | 10.8 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 1.21 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 12.4 µm/m·°C (20–300°C) | ASTM E228 |
Specific Heat Capacity | 420 J/kg·K at 20°C | ASTM E1269 |
Elastic Modulus | 200 GPa at 20°C | ASTM E111 |
Mechanical Properties (Annealed Condition)
Property | Value (Typical) | Test Standard |
|---|---|---|
Tensile Strength | 690–760 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 275–345 MPa | ASTM E8/E8M |
Elongation | ≥45% (25mm gauge) | ASTM E8/E8M |
Hardness | 180–220 HB | ASTM E10 |
Impact Toughness | Excellent at ambient and cryogenic temperatures | ASTM E23 |
Key Characteristics of Hastelloy C-4
Thermal Stability: Maintains corrosion resistance after prolonged exposure at 650–1040°C, resisting grain boundary sensitization common in welded components.
Oxidizing Acid Resistance: Corrosion rate <0.02 mm/year in boiling 65% nitric acid, outperforming stainless steel and other nickel alloys.
Low Embrittlement Risk: The alloy remains ductile even after extended service due to controlled carbon and silicon content.
CNC Machining Compatibility: Suitable for tight-tolerance applications (±0.01 mm), offering dimensional stability in both roughing and finishing processes.
CNC Machining Challenges and Solutions for Hastelloy C-4
Machining Challenges
Work Hardening
Cutting zones rapidly harden, increasing tool wear and requiring careful management of feed rates and depth of cut.
Heat Retention
With thermal conductivity <11 W/m·K, excessive heat buildup at the cutting edge can lead to tool failure and surface degradation.
BUE Formation
High alloy content can result in built-up edge (BUE) formation on uncoated tools, affecting part finish and dimensional accuracy.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | Carbide (K20–K30 grade) or ceramic inserts | Maintains hardness at elevated temperatures |
Coating | AlTiN or AlCrN (3–5 µm) | Reduces tool wear and chip adhesion |
Geometry | Positive rake (10–12°), sharp cutting edge (hone radius 0.02–0.05 mm) | Enhances chip evacuation and surface finish |
Cutting Parameters (ISO 3685)
Operation | Speed (m/min) | Feed (mm/rev) | DOC (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 12–20 | 0.20–0.30 | 2.0–3.0 | 90–120 |
Finishing | 25–35 | 0.05–0.10 | 0.5–1.0 | 120–150 |
Surface Treatment for Machined Hastelloy C-4 Parts
Hot Isostatic Pressing (HIP)
HIP at 100–200 MPa and 1150°C for 2–4 hours eliminates internal porosity and enhances fatigue life in cast or AM parts.
Heat Treatment
Heat Treatment involves annealing at 1120–1175°C for 1–2 hours, followed by rapid quenching to prevent grain boundary carbide formation.
Superalloy Welding
Superalloy Welding uses GTAW with ERNiCrMo-4 filler and interpass temperatures <120°C to avoid sensitization, ensuring post-weld corrosion rates remain below 0.02 mm/year.
Thermal Barrier Coating (TBC)
TBC Coating up to 250 µm thick provides insulation for parts exposed to acid vapors and thermal cycling above 800°C.
Electrical Discharge Machining (EDM)
EDM enables precise contouring of intricate parts with tolerances as tight as ±0.005 mm and Ra <0.8 µm.
Deep Hole Drilling
Deep Hole Drilling allows hole depths up to 30× diameter with internal cooling, ideal for heat exchanger baffles and scrubber assemblies.
Material Testing and Analysis
Material Testing includes sensitization (ASTM A262 Practice E), mechanical testing (ASTM E8/E18), and microstructure mapping via SEM/EDS.
Industry Applications of Hastelloy C-4 Components
Flue Gas Desulfurization (FGD) Systems
Ducting, fan housings, and mist eliminators exposed to SO₂, HCl, and acidic condensates up to 180°C.
Chemical Processing Equipment
Reactor liners, agitators, and piping systems in nitric, phosphoric, and sulfuric acid streams.
Pulp and Paper Industry
Digesters and bleach plant components resistant to acidic bleach liquors.
Pharmaceutical and Food-Grade Equipment
Non-contaminating, corrosion-resistant linings and fittings exposed to aggressive cleaning and sterilization agents.
FAQs
What sets Hastelloy C-4 apart from other C-series alloys regarding thermal and corrosion stability?
How should CNC tools and parameters be optimized for Hastelloy C-4 machining?
Does Hastelloy C-4 require post-weld heat treatment to maintain corrosion resistance?
In what chemical environments does Hastelloy C-4 outperform stainless steel?
What industry standards does Hastelloy C-4 meet for high-purity or aggressive applications?
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