Q1: What is UNS N06455 Plate, and what are its core material identity, chemical composition, and global equivalent grades?
UNS N06455 Plate, commonly known as Hastelloy® C4 plate, is a low‑carbon, austenitic nickel‑chromium‑molybdenum (Ni‑Cr‑Mo) corrosion‑resistant alloy plate designed for extreme corrosive environments. It is widely recognized as one of the most thermally stable alloys in the Ni‑Cr‑Mo family, with tightly controlled chemical composition to minimize harmful intermetallic phase precipitation during welding or high‑temperature service.
The typical chemical composition (weight %) is:
Ni: balance (base element)
Cr: 14.5–17.5%
Mo: 15.0–17.0%
C: ≤0.009% (ultra‑low carbon to reduce carbide precipitation)
Fe: ≤3.0%
Si: ≤0.50%
Mn: ≤1.00%
Ti: trace stabilization
P, S: ≤0.020%, ≤0.010% respectively
Global equivalent grades include:
Europe: W.Nr. 2.4610, EN designation NiMo16Cr16Ti
China: NS335
USA: Hastelloy C4, UNS N06455
ASME: SB‑575 / SB‑619 / SB‑622
This material is produced in plate, sheet, strip, pipe, bar, and forging forms. Plates are usually supplied in hot‑rolled, annealed, pickled, and straightened condition, with thickness ranging from 2 mm up to 100 mm or more for heavy industrial equipment. Its unique composition delivers excellent ductility, weldability, and resistance to localized and uniform corrosion, making it irreplaceable in chemical processing, flue gas desulfurization, and waste treatment industries.
Q2: What are the key mechanical and physical properties of UNS N06455 Plate that determine its industrial performance?
UNS N06455 Plate exhibits a well‑balanced combination of mechanical strength, ductility, and thermal stability, which are critical for structural integrity in harsh service conditions.
Key mechanical properties (annealed condition):
Tensile strength: ≥690 MPa
Yield strength (0.2% offset): ≥310 MPa
Elongation: ≥40% (excellent ductility for forming and bending)
Hardness: typically 180–240 HB (soft enough for machining and welding)
Physical properties:
Density: 8.69 g/cm³
Melting range: 1350–1390 °C
Thermal conductivity: ~10.8 W/m·K
Electrical resistivity: ~1.28 μΩ·m
The most outstanding performance feature is excellent thermal stability. Unlike many other Ni‑Cr‑Mo alloys, UNS N06455 retains high ductility and corrosion resistance even after long‑term aging in the temperature range of 650–1040 °C, where other alloys may suffer from severe embrittlement due to intermetallic phase formation. This stability makes it ideal for equipment that operates under cyclic heating and cooling, such as reactors, heat exchangers, and piping systems.
In addition, the alloy shows good workability despite moderate work‑hardening. It can be hot and cold formed, rolled, punched, spun, and deep‑drawn using standard fabrication methods. These properties ensure that UNS N06455 Plate can be reliably manufactured into complex components without cracking or performance degradation.
Q3: What exceptional corrosion resistance does UNS N06455 Plate provide, and in what aggressive media does it excel?
UNS N06455 Plate is engineered for universal corrosion resistance in both oxidizing and reducing environments, making it superior to many 300‑series stainless steels, duplex stainless steels, and even some nickel alloys.
Its main corrosion resistances are:
Pitting and crevice corrosion resistanceHigh chromium and molybdenum content provides outstanding resistance to chloride‑induced pitting and crevice attack, which is critical in seawater, brine, and chloride‑containing chemical processes.
Stress corrosion cracking (SCC) resistanceAs a nickel‑based austenitic alloy, it is essentially immune to chloride SCC that often plagues austenitic stainless steels like 304 and 316L under high temperature and stress.
Uniform corrosion resistancePerforms well in oxidizing acids (e.g., dilute nitric acid), reducing acids (e.g., hydrochloric, sulfuric, phosphoric acids), organic acids, and alkaline solutions.
High‑temperature corrosion resistanceResists oxidation, carburization, and chloride attack at elevated temperatures up to approximately 1040 °C, suitable for flue gas desulfurization (FGD), incineration, and thermal processing systems.
Welded zone corrosion resistanceUltra‑low carbon and titanium stabilization minimize carbide precipitation at grain boundaries during welding, preserving corrosion resistance in heat‑affected zones (HAZ) without post‑weld heat treatment (PWHT).
It is widely used in environments containing chlorides, fluorides, sulfur compounds, and mixed acids, where less corrosion‑resistant materials would fail rapidly.
Q4: What are the main industrial applications of UNS N06455 Plate, and why is it preferred over similar alloys?
UNS N06455 Plate is a high‑performance corrosion‑resistant alloy used in critical sectors where equipment lifespan, safety, and reliability are non‑negotiable.
Major industries and applications:
Chemical processing industryReactors, heat exchangers, columns, tanks, and piping for handling sulfuric acid, hydrochloric acid, organic acids, and intermediate chemicals.
Flue gas desulfurization (FGD) systemsAbsorber vessels, ductwork, and scrubber components in power plants exposed to highly corrosive flue gas and wet limestone slurry.
Pollution control and waste treatmentIncinerator liners, waste liquid treatment tanks, and ventilation systems handling corrosive waste gases and liquids.
Petrochemical and oil & gas
Separation units, pipelines, and pressure vessels in sour gas (H₂S, chloride) environments.
Pharmaceutical and fine chemical manufacturingReactors and storage tanks requiring high purity and corrosion resistance to avoid product contamination.
Why it is preferred over similar alloys (e.g., C276, C22):
Superior thermal stability – less likely to become brittle after long‑term high‑temperature exposure.
Better weldability and HAZ corrosion resistance – ideal for heavily welded structures.
Balanced cost and performance – provides reliable protection at a more controlled cost than some ultra‑high‑grade alloys.
Proven track record – widely certified and used in global industrial standards for critical equipment.
It is often selected when C276 shows excessive aging embrittlement or when post‑weld heat treatment is impractical.
Q5: What are the standard specifications, fabrication guidelines, and quality control requirements for UNS N06455 Plate?
UNS N06455 Plate must comply with strict international standards to ensure material consistency, mechanical performance, and corrosion resistance.
Main applicable standards:
ASTM: B575 (plate, sheet, strip)
ASME: SB‑575, SB‑619, SB‑622
EN: 10028‑7 (Ni alloy plates for pressure purposes)
GB/T: 15002, 20547 (Chinese nickel‑based alloy plates)
Available dimensions:
Thickness: 2 mm – 100+ mm
Width: 1000 mm – 2500 mm
Length: 2000 mm – 6000 mm or customized
Surface: pickled, bright annealed, polished (2B, BA, No.4)
Fabrication guidelines:
Forming: Can be cold formed; tools must be clean to avoid iron contamination.
Welding: Use matching filler metals (e.g., AWS A5.14 ERNiCrMo‑7); clean before welding; no PWHT required.
Machining: Best in annealed condition; use sharp tools and low cutting speeds due to work‑hardening.
Heat treatment: Annealing at 1177–1232 °C followed by rapid cooling to ensure optimal corrosion resistance and ductility.
Quality control requirements:
Mill test certificate (MTC) according to EN 10204 3.1 or 3.2
Chemical composition analysis by OES or XRF
Mechanical property testing (tensile, hardness, bend)
Intergranular corrosion test (e.g., ASTM G28)
Ultrasonic testing (UT) for plate internal defects
Dimensional inspection and surface quality check
Strict quality assurance ensures that UNS N06455 Plate meets design codes for pressure vessels, nuclear‑related components, and chemical equipment.
