What is Incoloy 825 alloy steel?

 　　A newcomer asked: nickel based alloys Incoloy 825, Inconel 600, Monel 400, Hastelloy C-276, etc. What is nickel based alloy?

　　In fact, Incoloy825 alloy is an iron nickel based corrosion-resistant alloy. Iron nickel based alloys are some grades between high nickel austenitic stainless steel and nickel based corrosion-resistant alloys. General regulations: Ni content ≥ 30%, Ni+Fe content ≥ 60%. Compared with nickel based alloys, this type of alloy can save nearly 40% to 50% of nickel. On the premise of ensuring that the alloy matrix has a face centered cubic structure of austenite structure, iron nickel based corrosion resistant alloys can accommodate more chromium that is conducive to improving the corrosion resistance of the alloy compared to chromium nickel austenitic stainless steel. The content of molybdenum and other elements, and the thermal stability of the alloy is generally still better than high chromium. Chromium nickel austenitic stainless steel with molybdenum content.

　　The newcomer finally understands that Incoloy 825 alloy is an iron nickel based corrosion-resistant alloy. So today we can talk about Incoloy 825 alloy knowledge.

　　It is called 0Cr21Ni42Mo3Cu2Ti domestically. It is only called Incoloy 825 in foreign countries, also known as Ni-O-Nel 825 or Ni-O-Nel alloy. Secondary alloy is a titanium stabilized Ni Fe Cr Mo Cu corrosion-resistant alloy with good overall and local corrosion resistance, and good process performance.

　　Oh, what are the structural characteristics of Incoloy 825 alloy?

　　The equilibrium relationship between nickel equivalent and chromium equivalent in the composition of Incoloy 825 alloy determines that this alloy has a pure austenite structure under solid solution conditions. However, during medium temperature aging, carbides and intermetallic compounds will precipitate on the austenitic matrix and intergranular surfaces, which can harm the mechanical and corrosion resistance of the alloy.

　　How about the corrosion resistance of Incoloy 825 alloy?

　　1. Comprehensive corrosion: In the atmosphere, this alloy is resistant to atmospheric corrosion in rural, industrial, and marine environments. However, in atmospheres with high chloride content, especially in humid atmospheres, this alloy can produce very shallow pitting corrosion. In freshwater, this alloy is resistant to freshwater corrosion, including the most corrosive chlorides containing free CO ₂ and iron compounds, natural water, and various industrial cooling water containing impurities. Its corrosion rate is usually lower than 0.0025mm/a. In seawater, this alloy is resistant to corrosion in high-speed seawater, and can produce certain corrosion in static and low-speed seawater or polluted seawater conditions.

　　In sulfuric acid, the corrosion resistance of this alloy is roughly equivalent to 0Cr22Ni47Mo6.5Cu2Nb2, but the usage temperature is slightly lower. In sulfuric acid filled with air at 65 ℃, when the concentration is less than 20%, there is no significant effect on the corrosion resistance of the alloy with the increase of concentration. In sulfuric acid above 40%, the corrosion of the alloy intensifies with the increase of concentration. In practical applications, sulfuric acid often contains various impurities. In addition to chloride impurities, HNO Å, Fe ₂ (SO4) Å, CuSO4, nitrate, persulfate, permanganate, etc. can promote alloy passivation and reduce corrosion. In this environment, the temperature of alloy use can be correspondingly increased compared to pure H ₂ SO4.

　　In phosphoric acid, in reagent grade phosphoric acid, this alloy is corrosion-resistant in H Å PO4 below 85% until boiling temperature. The on-site test data of this alloy in a wet process phosphoric acid factory shows that Incoloy 825 also has good corrosion resistance in slurry containing F - and other impurities, but it is not as good as the high chromium Ni Fe Cr Mo Cu alloy.

　　In hydrochloric acid, Incoloy 825 alloy was tested in different concentrations of hydrochloric acid, and this alloy can only be used in dilute acid solutions at room temperature.

　　In hydrofluoric acid and fluorosilicic acid, this alloy has poor corrosion resistance in hydrofluoric acid and only has moderate corrosion resistance under a few conditions, and is generally not recommended for use in pure hydrofluoric acid. The corrosion resistance of fluorosilicic acid is lighter than that of hydrofluoric acid. In fluorosilicic acid containing impurities, this alloy has good corrosion resistance and can be used at 60 ℃.

　　In sulfite, 0Cr21Ni42Mo3Cu2Ti is resistant to wet SO ₂ and sulfite solutions, and has a wide range of applications, especially in sulfite solutions containing H ₂ SO4. This alloy has better corrosion resistance than alloys containing the same chromium and molybdenum without copper.

　　In nitric acid, Incoloy alloy exhibits good corrosion resistance in all concentrations of nitric acid at boiling temperature. In dilute nitric acid, it can be used up to temperatures above the boiling point. It also exhibits good corrosion resistance in room temperature fuming nitric acid and 70 ℃ fuming nitric acid with corrosion inhibitors. In organic acids and compounds, this alloy exhibits high corrosion resistance and can be applied over a wide temperature range. At boiling temperature, except for 10% oxalic acid, it is resistant to corrosion in most 10% organic acids and exhibits excellent corrosion resistance during organic processing.

　　Below will be intergranular corrosion, which is not sensitive to solid solution treatment at 1150~1204 ℃. When subjected to intermediate temperature sensitization treatment for 1 hour, such as 760 ℃, chromium rich M23C6 precipitates will appear at grain boundaries, leading to intergranular corrosion in boiling 65% HNO. However, stabilizing at 940 ℃ for 1 hour before sensitization can prevent intergranular corrosion caused by sensitization.

　　Spot corrosion, the corrosion resistance of Incoloy 825 alloy in oxidizing acidic chlorides is obviously poor in such media.

　　Stress corrosion cracking resistance of Incoloy 825 alloy in alkali and MgCl ₂ is good.

　　What are the hot and cold working and forming properties of Incoloy 825 alloy steel?

　　The hot forming temperature of this alloy is 927~1065 ℃, and it is not suitable to perform forming operations at a temperature sensitive to intergranular corrosion of 650 ℃. If formed above 1065 ℃, the final forming should be carried out in the range of 870~980 ℃ to achieve good intergranular corrosion resistance. This alloy is also suitable for cold working forming.

　　How about the heat treatment process?

　　This alloy is suitable for stabilization treatment at 940 ℃ during the hottest treatment. The intermediate annealing temperature should be higher than the solution softening annealing temperature of 1050 ℃.

　　How about the welding performance?

　　The usual welding method can be used for welding.

　　Which fields are commonly used?

　　Mainly used in the chemical industry, hot seawater, and water treatment plants. Mainly used for treating heat exchangers, pipelines, valves, pumps, etc. in environments such as hot sulfuric acid, chloride containing solutions, and sulfite. It is also used in the paper industry.