UNS N08028 / W.Nr. 1.4563 / Nic28 / NiCro 31/27
Alloy 28 is a nickel-iron-chromium alloy with additions of molybdenum and copper. It has excellent resistance to both reducing and oxidizing acids, to stress-corrosion cracking, and to localise attack such as pitting and crevice corrosion. The alloy are especially resistant to sulphuric and phosphoric acid. Used for chemical processing, pollution control equipment, oil and gas well piping, nuclear fuel reprocessing, acid production and pickling equipment.
• Production, concentration and use of phosphoric acid reactors tanks, impellers, piping systems, cyclone evaporators, surface coolers, circulation pumps, agitators, superphosphoric acid storage, shell/tubes for heat exchangers
• Production and use of sulphuric acid: heating equipment, reactor tanks, agitators, inlet pipe in reactors...
• Oil and gas production : sour gas application, tubing, separators...
• Several offshore platform equipment
• Chemical industry (acetic acid, vinyl chlorides)
|
Grade |
C |
Si |
Mn |
P |
Cr |
Mo |
Ni |
N |
|
Alloy 28 |
0.02 max |
0.70 max |
2.00 max |
0.03 max |
26.00 – 28.00 |
30.00 – 32.00 |
19.00 – 21.00 |
0.11 max |
|
Element |
Hardness |
Yield Strength (0.2%Offset) |
Tensile Strength |
Elongation |
|
Alloy 28 |
230 |
220 |
500 – 750 |
30 % |
Alloy 28 has excellent resistance to strong acids, including phosphoric, hydrochloric, nitric, formic, and sulfuric acids. Its resistance to pitting and corrosion resistance makes it suitable for seawater piping and heat exchangers.
Recommended working and heat treatment parameters for alloy 28:
Forging: 1150-850 ℃
Rolling: 1150-850 ℃
Solutioning: 1050-1150 ℃
Solution Annealing: Solution annealing is a heat treatment process that involves heating the material to a specific temperature range to dissolve any precipitates or impurities in the material. For N08028, the solution annealing temperature typically ranges from about 1050°C to 1150°C (1922°F to 2102°F).
Stress Relieving: Stress relieving is another heat treatment process used to reduce internal stresses in the material that may have been introduced during fabrication processes such as welding or forming. The stress relieving temperature for N08028 stainless steel is usually in the range of 550°C to 650°C (1022°F to 1202°F).
Pickling Temperature: Pickling, which is a chemical treatment to remove scale and impurities from the surface of the material, is typically done at lower temperatures. The pickling temperature for N08028 stainless steel is usually around room temperature or slightly elevated, depending on the specific pickling solution being used.
Pickling is a common process used to remove surface impurities and oxide layers from Nitronic 32 stainless steel. It involves immersing the material in a pickling solution, typically an acid-based solution, to dissolve contaminants and restore the material's corrosion resistance. During the pickling process, it is crucial to control the concentration and temperature of the pickling solution to prevent excessive etching or corrosion of the stainless steel surface.
Hot Forming Temperature: The hot forming temperature for N08028 typically ranges from around 1100°C to 1250°C (2012°F to 2282°F).
Forming Process: Hot forming involves heating the material to high temperatures to make it more malleable and easier to shape. It is important to maintain the appropriate temperature range to prevent work hardening and cracking during forming.
Equipment: Hot forming of N08028 may involve processes such as hot rolling, hot forging, or extrusion, depending on the desired shape and properties of the final product.
Post-Forming Treatment: After hot forming, the material may require further heat treatment processes such as annealing or stress relieving to optimize its properties.
The machining of alloy 28, as with other stainless steels, requires an adjustment of tooling data and machining method, in order to achieve satisfactory results. Compared to 316/316L, the cutting speed must be reduced by approximately 50-55% when turning alloy 28 with coated, cemented carbide tools. Much the same applies to other operations. Feeds should only be reduced slightly and with care.
The weldability of alloy 28 is good. Suitable methods of fusion welding are manual metal-arc welding (MMA/SMAW) and gas-shielded arc welding, with the TIG/GTAW method as first choice.
In common with all fully austenitic stainless steels, alloy 28 has low thermal conductivity and high thermal expansion. Welding plans should therefore be carefully selected in advance, so that distortions of the welded joint are minimized. If residual stresses are a concern, solution annealing can be performed after welding.
For alloy 28, heat-input of <1.0 kJ/mm and interpass temperature of <150°C (300°F) are recommended. A string bead welding technique should be used.
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