Hastelloy C-4 Alloy | N06455 | 2.4610 | W-Free Thermal Stable | Fushun Metal

Hastelloy C-4 / N06455 / 2.4610 — Introduction

Hastelloy C-4, designated UNS N06455 and Werkstoff Nr. 2.4610, is a nickel-chromium-molybdenum corrosion-resistant alloy engineered specifically to overcome the thermal instability that limits the C-276 and C-22 variants. By eliminating tungsten and tightly restricting iron, C-4 achieves virtual immunity to intergranular precipitation of embrittling mu-phase and carbide phases across the 650–1040°C temperature range—the critical window where most Ni-Cr-Mo alloys suffer catastrophic loss of ductility and corrosion resistance after thermal exposure. It retains essentially the same outstanding resistance to hydrochloric acid, sulfuric acid, chlorides, and stress corrosion cracking as C-276, but with the decisive advantage that it can be welded, hot-formed, and operated at sustained elevated temperatures without requiring post-fabrication solution annealing. This thermal stability makes C-4 the alloy of choice for chemical plant equipment subjected to upset conditions, nuclear fuel reprocessing dissolvers and evaporators, and pesticide/agrochemical reactor systems operating continuously above 400°C in corrosive halogenated environments.

At Fushun Metal, Hastelloy C-4 is manufactured through a fully integrated triple-melt route under one roof. VIM primary melting under high vacuum ensures the ultra-low carbon level (≤0.015%) and precise titanium recovery essential for tying up residual carbon as stable TiC rather than chromium carbides. The VIM electrode undergoes VAR, where controlled directional solidification produces chemically homogeneous, low-inclusion material with minimal segregation of molybdenum—a heavy element prone to micro-banding in less controlled solidification. For nuclear, agrochemical, and critical chemical plant applications where long-term microstructural integrity under thermal cycling is the overriding specification requirement, we deploy PESR as the final stage, achieving deep desulfurization and oxide refinement through argon-shielded reactive slag chemistry.

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 connects each production lot from melt heat number through remelt sequence, hot-working reduction ratio, and final annealing batch. Standard deliverables include intergranular corrosion testing per ASTM G28 Method A and B, ultrasonic inspection, chemical re-verification by optical emission and LECO combustion, and room-temperature tensile testing. Mill test certificates to EN 10204 3.1 or 3.2 accompany every shipment.

Equivalent Grades of Hastelloy C-4 Across International Standards

Hastelloy C-4 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 Hastelloy C-4

Hastelloy C-4 is specified where the process environment demands both the broad-spectrum corrosion resistance of the C-family alloys and sustained thermal stability at temperatures where C-276 and C-22 embrittle. It is the alloy of choice for welded or hot-formed components that must retain full ductility and intergranular corrosion resistance in the as-fabricated condition—without post-weld solution annealing—and for equipment exposed to prolonged thermal cycling between ambient and process temperatures exceeding 400°C in corrosive service.

Hastelloy C-4 — Supply Range by Fushun Metal

Fushun Metal stocks and processes Hastelloy C-4 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 B574 / B575 (typically 1065°C, rapid water quench). Due to C-4’s superior thermal stability, welded fabrications can be placed in service without post-weld solution annealing in most chemical environments—a significant cost and lead-time advantage. Intergranular corrosion testing per ASTM G28 Method A and B is standard on every heat. Mill test certificates to EN 10204 3.1 or 3.2 accompany every shipment.

Chemical Composition of Hastelloy C-4 — ASTM B574 / ASTM B575

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 defining compositional feature of C-4 is the deliberate exclusion of tungsten—the element responsible for mu-phase embrittlement in C-276 during exposure to the 650–1040°C range. The controlled titanium addition (≤0.70%) preferentially forms stable TiC carbides, suppressing chromium carbide precipitation at grain boundaries and further enhancing thermal stability during welding and elevated-temperature service.

Mechanical Properties of Hastelloy C-4 — Per Product Form

Hastelloy C-4 is a solid-solution-strengthened nickel alloy; all mechanical properties are developed through hot-working and final solution annealing at approximately 1065°C followed by rapid water quenching. The alloy is not hardenable by heat treatment. Its tungsten-free composition ensures that mechanical properties—particularly elongation and impact toughness—are retained after prolonged exposure to the 650–1040°C sensitization range, a performance characteristic that distinguishes it from C-276 and C-22 in thermal processing, nuclear, and high-temperature chemical plant applications operating above 400°C.

Fushun Metal performs all solution annealing in-house under calibrated furnace controls with rapid water-quench capability. Post-weld solution annealing is generally not required—the alloy’s superior thermal stability permits as-welded service in most chemical environments. This eliminates a major fabrication bottleneck and reduces equipment delivery lead times compared to C-276 fabrications that demand PWHT. Where welding is performed, matching ERNiCrMo-7 filler metal (GTAW) or ENiCrMo-7 electrodes (SMAW) are recommended, with standard Ni-Cr-Mo welding practices: low heat input, interpass temperature control below 100°C, and argon back-purge.

Physical constants: Density 8.64 g/cm³; Melting range 1335–1380°C; Hardness ≤100 HRB (annealed condition); Modulus of elasticity 211 GPa at 20°C; Thermal conductivity 10.1 W/m·K at 20°C; Coefficient of thermal expansion 13.3 μm/m·°C (20–538°C). The alloy is non-magnetic and retains full ductility after 100+ hours of aging at 700°C.