How strong is Inconel 625?
Description
Alloy 625 is a non-magnetic, corrosion- and oxidation-resistant nickel-based alloy. Its excellent strength and toughness in the cryogenic to 2000°F (1093°C) temperature range is primarily due to the solid solution effect of the refractory metals niobium and molybdenum in a nickel-chromium matrix. The alloy has excellent fatigue strength and resistance to chloride stress corrosion cracking. Some typical applications for Alloy 625 include heat shields, furnace hardware, gas turbine engine ducting, combustion liners and spray bars, chemical plant hardware, and special seawater applications.
Corrosion Resistance
Alloy 625 withstands a wide range of corrosive environments. Corrosion is virtually nonexistent in alkaline, saltwater, freshwater, neutral salts, and air. Nickel and chromium resist oxidizing environments. Nickel and molybdenum resist non-oxidizing atmospheres. Molybdenum protects against pitting and crevice corrosion. Niobium stabilizes the alloy against sensitization during welding. Resistance to chloride stress corrosion cracking is excellent. The alloy resists scaling and oxidation at elevated temperatures.
Pickling
A sodium hydride bath is required to remove scale from this alloy. After the sodium hydride treatment, the material should be immersed in a sulfuric acid bath at 165°F (74°C) for approximately 3 minutes. This is followed by a 25 minute soak in a nitric-hydrofluoric acid bath at 145°F (63°C). Rinse. Sulfuric acid solution: 16% H2SO4 by weight. Nitric acid solution: 8% HNO3 by weight and 3% HF by weight. Acid etching for macroscopic examination - electrolytically expose the material to a 3:1 solution of HCl and HNO3, saturated with CuCl2, at a current density of 0.645 A/in2 (25.4 A/m)
