Chemical composition of nickel - Knowledge

1.What is the nickel content range of Incoloy 825 alloy plate?

The nickel content range of Incoloy 825 alloy plate is strictly defined as 38.0%–46.0% by weight, in accordance with globally recognized industry standards including ASTM B424 (Standard Specification for Nickel-Iron-Chromium-Molybdenum-Columbium Alloy Plate, Sheet, and Strip) and ASME SB424. Nickel is the core alloying element of Incoloy 825; this specific content range endows the alloy with exceptional resistance to general corrosion, pitting, crevice corrosion, and stress corrosion cracking in aggressive media such as sulfuric acid, phosphoric acid, and chloride-containing solutions. Meanwhile, it maintains the alloy's high-temperature mechanical stability and toughness, making it suitable for service in both ambient and elevated temperature environments.

2.What is the carbon content control standard for Incoloy 825?

The carbon content of Incoloy 825 is strictly controlled to a maximum limit of 0.05% by weight, as mandated by standards like ASTM B424 and ASME SB424. The strict limitation of carbon content serves two vital and irreplaceable technical functions:

Prevention of intergranular corrosion: During welding processes or long-term service at medium temperatures (typically between 427°C and 815°C), excessive carbon tends to react with chromium in the alloy to form chromium carbides (e.g., Cr₂₃C₆) and precipitate along the grain boundaries. This precipitation depletes the chromium content in the adjacent matrix, creating a "chromium-depleted zone" that is highly susceptible to corrosion. By limiting carbon to ≤0.05%, the formation of such chromium carbides is effectively inhibited, thus preserving the alloy's uniform corrosion resistance and avoiding catastrophic intergranular corrosion failures in corrosive working conditions.

Enhancement of weldability: Low carbon content reduces the risk of forming brittle phases (such as martensite or other hard and brittle intermetallic compounds) in the weld heat-affected zone (HAZ) during welding. This ensures that the welded joints retain mechanical properties (e.g., tensile strength, ductility, and impact toughness) and corrosion resistance that are comparable to the base metal. It also minimizes the tendency of weld cracking, simplifying the welding operation and improving the reliability of welded structures made of Incoloy 825.