What is the difference between nickel-based materials and stainless steel?

This post was last edited by realben on 2011-2-16 09:07. Nickel-based alloys are based on nickel, with a nickel content of over 50%; in contrast, the nickel content in 300-grade stainless steel is only a little over 20%. Naturally, nickel-based alloys have better resistance to acids, alkalis, and degradation due to high temperatures. They are also more expensive. Here is a recommendation for a related material: http://bbs.hcbbs.com/viewthread.php?tid=739765. There’s also this article: http://bbs.hcbbs.com/thread-780730-1-1.html

Nickel-based alloys are superior to three-metal alloys, both in terms of corrosion resistance and high-temperature tolerance. Generally, nickel-based alloys are divided into two categories: nickel-chromium-iron (high-temperature resistant alloys) and nickel-chromium-molybdenum (corrosion-resistant alloys). Alloys like 625 belong to the nickel-chromium-molybdenum-niobium category; they possess excellent corrosion resistance and high-temperature resistance. At temperatures as low as 1093 degrees Celsius, these alloys maintain good strength, toughness, and outstanding fatigue resistance. As mentioned earlier, the key difference lies in the elements used – nickel is a rare and valuable element that confers strong corrosion resistance to steel. Typically, its price is much higher than that of three-metal alloys

Inconel 625 (UNS N06625/W.Nr.2.4856) Chemical composition of Inconel 625: Alloy % Nickel Chromium Molybdenum Niobium Tantalum Iron Aluminum Titanium Carbon Manganese Silicon Copper Phosphorus Sulfur – Minimum 58, 20, 83.15; Maximum 23, 10, 4.15, 50.40, 0.40, 0.10, 0.50, 0.50, 0.50, 0.015, 0.015. Physical properties of Inconel 625: Density 8.4 g/cm3; Melting point 1290–1350°C. Minimum mechanical properties of the alloy at room temperature: Tensile strength Rm in N/mm2, Yield strength RP0.2 in N/mm2, Elongation A5 in %, Brinell hardness HB – 625, 760, 345, 30; ≤220. This alloy possesses the following characteristics: 1. Excellent corrosion resistance against various corrosive agents in both oxidizing and reducing environments. 2. Good resistance to pitting and crevice corrosion, without susceptibility to stress corrosion cracking caused by chlorides. 3. Excellent resistance to corrosion by inorganic acids such as nitric acid, phosphoric acid, sulfuric acid, hydrochloric acid, and mixed acids of sulfuric and hydrochloric acids. 4. Good resistance to corrosion in various mixed solutions of inorganic acids. 5. It maintains good corrosion resistance in hydrochloric acid solutions of various concentrations at temperatures up to 40°C. 6. Good workability and weldability, with no sensitivity to crack formation after welding. 7. It is approved for use in pressure vessels with wall temperatures ranging from -196 to 450°C. 8. It meets the highest standard grade VIII for use in acidic gas environments, as certified by the American Society of Corrosion Engineers’ NACE standard (MR-01-75). Microstructural structure of Inconel 625: Inconel 625 has a face-centered cubic crystal structure. After being held at about 650°C for a sufficient length of time, the precipitated carbon particles and unstable tetragonal phases will transform into the stable Ni3(Nb,Ti) rhombohedral lattice phase. After solution strengthening, the molybdenum and niobium contents in the nickel-chromium matrix improve the mechanical properties of the material, but its plasticity decreases. Corrosion resistance of Inconel 625: The 625 alloy exhibits excellent corrosion resistance in many media. It exhibits excellent resistance to pitting corrosion, crevice corrosion, intergranular corrosion, and erosion in chloride media. It exhibits excellent resistance to corrosion by inorganic acids such as nitric acid, phosphoric acid, sulfuric acid, and hydrochloric acid, and it also shows resistance to corrosion by alkalis and organic acids in both oxidizing and reducing environments. Effective resistance to chloride-induced reduction stress corrosion cracking. It exhibits almost no corrosion in seawater and industrial gas environments, showing high corrosion resistance to seawater and salt solutions, as well as at high temperatures. No sensitivity during welding. It exhibits resistance to carburization and oxidation in both static and cyclic environments, as well as resistance to corrosion by chlorinated gases. Applications of Inconel 625: The low-carbon alloy 625, after soft annealing, is widely used in the chemical processing industry. Its good corrosion resistance and high strength enable it to be used as thin structural components. 625 alloy can be used in applications that are exposed to seawater and subject to high mechanical stresses. Typical application areas: 1. Components in organic chemical processes involving chlorides, especially in cases where acidic chloride catalysts are used. 2. Cookers and bleaching tanks in the pulp and paper industry. 3. Absorption towers, reheaters, flue gas inlet dampers, fans (wet type), agitators, guide vanes, and flues in flue gas desulfurization systems. 4. Equipment and components designed for use in environments with acidic gases. 5. Reactors for the reaction between acetic acid and acetic anhydride. 6. Sulfuric acid condensers