Incoloy 20 Alloy | N08020 | 2.4660 | Cu-Nb H2SO4 Resistant | Fushun Metal

Incoloy 20 / N08020 / 2.4660 — Introduction

Incoloy 20, designated UNS N08020 and Werkstoff Nr. 2.4660 (also widely known as Alloy 20, 20Cb-3, or Carpenter 20), is a niobium-stabilized austenitic nickel-iron-chromium alloy with deliberate additions of copper and molybdenum. Its defining compositional feature—3–4% copper—provides resistance to sulfuric acid that no conventional stainless steel can match, while the 32–38% nickel content renders it virtually immune to chloride stress corrosion cracking. Niobium stabilization (Nb ≥ 8 x C) ties up carbon as stable niobium carbides, preventing chromium carbide precipitation at grain boundaries during welding or elevated-temperature exposure, and eliminating the need for post-weld solution annealing to restore intergranular corrosion resistance—a critical practical advantage in field-fabricated chemical plant equipment.

At Fushun Metal, Incoloy 20 is manufactured through a fully integrated triple-melt route under one roof. VIM primary melting under high vacuum ensures precise recovery of the copper addition—an element prone to segregation in air-melted heats—while maintaining the ultra-low tramp-element levels required for optimal weldability. The VIM electrode then passes to VAR, where controlled directional solidification eliminates macro-segregation and produces chemically homogeneous electrode stock. For the most demanding applications—hot sulfuric acid alkylation units, pharmaceutical reactor vessels, and food-grade processing equipment where pitting cannot be tolerated—we deploy PESR as the final stage, achieving deep desulfurization and inclusion refinement through argon-shielded reactive slag chemistry.

Every heat is processed, forged, rolled, solution-annealed, 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 connects each production lot from melt heat number through remelt sequence, hot-working reduction ratio, and solution-annealing batch. Standard deliverables include intergranular corrosion testing per ASTM A262 Practice C (Huey test), ultrasonic inspection, chemical re-verification by optical emission and LECO combustion analysis, and room-temperature tensile testing. Mill test certificates to EN 10204 3.1 or 3.2 accompany every shipment.

Equivalent Grades of Incoloy 20 Across International Standards

Incoloy 20 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 20

Incoloy 20 is the established workhorse for equipment handling sulfuric acid at concentrations and temperatures that aggressively attack 304/316L stainless steels. Its copper-modified chemistry also provides outstanding resistance to phosphoric acid, nitric-sulfuric mixed acids, and chloride-bearing process streams. Typical maximum continuous service temperature in sulfuric acid environments is ~93°C, with short-term excursions to higher temperatures permissible depending on concentration and flow conditions.

Incoloy 20 — Supply Range by Fushun Metal

Fushun Metal stocks and processes Incoloy 20 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 B463 / B473 (typical 982–1010°C, rapid air cool or water quench), fully recrystallized and verified free of sensitization. Intergranular corrosion testing per ASTM A262 Practice C is performed on each heat. Products are accompanied by mill test certificates to EN 10204 3.1 or 3.2 as required. Welding consumable recommendation: ERNiCrMo-3 (AWS A5.14) filler; ENiCrMo-3 (AWS A5.11) electrode.

Chemical Composition of Incoloy 20 — ASTM B463 / ASTM B473

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 copper (3–4%) and niobium (≥8xC) contents are the alloy’s compositional signatures—copper suppresses active dissolution in hot dilute sulfuric acid, while niobium preferentially forms stable NbC carbides that prevent chromium depletion at grain boundaries during welding and elevated-temperature service.

Mechanical Properties of Incoloy 20 — Per Product Form

Incoloy 20 is a solid-solution-strengthened austenitic alloy; all mechanical properties are developed through solution annealing at 982–1010°C followed by rapid air cooling or water quenching. The alloy is not hardenable by heat treatment. Its fully austenitic microstructure (stabilized by 32–38% nickel) provides exceptional ductility, toughness, and formability in the annealed condition, with cold-working being the only mechanism for increasing strength. The niobium stabilization ensures that mechanical properties at grain boundaries are maintained after welding without the need for post-weld heat treatment.

Fushun Metal performs all solution annealing in-house under calibrated furnace controls. For cold-formed components where residual stresses may promote stress corrosion cracking in service, a stress-relief anneal at 870–900°C for 1–2 hours followed by air cooling can be applied. Higher-temperature annealing must be followed by rapid cooling to avoid sensitization in the 540–815°C range. The recommended maximum continuous service temperature in oxidizing atmospheres is approximately 760°C, though in aggressive sulfuric acid environments the practical limit is determined by corrosion rate rather than mechanical strength and is typically below 100°C.

Physical constants: Density 8.08 g/cm³; Melting range 1370–1420°C; Hardness ≤217 HB (annealed condition, typical 170–200 HB); Modulus of elasticity 195 GPa at 20°C; Thermal conductivity ~12 W/m·K at 20°C; Coefficient of thermal expansion ~15 μm/m·°C (20–100°C). The alloy is non-magnetic due to its fully austenitic structure.