Alloy 825

Introduction

Incoloy 825 is highly resistant to corrosion. It has a high nickel content, sufficient to resist chloride ion stress corrosion cracking, and a very stable austenite structure. The levels of molybdenum and copper enable the alloy to resist reducing agents and acids. Chromium gives resistance to oxidising conditions, such as nitric acid solutions, nitrates and oxidising salts. The alloy is titanium stabilised to resist pitting and intergranular attack after fabrication, particularly welding, which includes heating in the critical sensitisation temperature range (650°C – 760°C). Alloy 825 offers exceptional resistance to corrosion by sulphuric and phosphoric acids and is often the most cost effective alloy in sulphuric acid service.

Equivalent Grades Of Alloy 825

Zeon Grade Alloy Name UNS EN / DIN / W Nr. Trademarks
Zeon825 Alloy 825 UNS N08825 2.4858 Incoloy 825

Chemical Composition Of Alloy 825

Elements %
Nickel 38.0 – 46.0
Chromium 19.5 – 23.5
Molybdenum 2.5 – 3.5
Copper 1.5 – 3.0
Titanium 0.6 – 1.2
Iron 22.0 min (~33%)
Carbon 0.05 max
Manganese 1.0 max
Sulfur 0.03 max
Silicon 0.5 max
Aluminium 0.2 max

Physical Properties Of Alloy 825

Density Melting Point Tensile Strength Yield Strength (0.2% Offset) Elongation
8.14g/cm3 1400°C (2550°F) Psi - 80,000 , MPa - 550 Psi - 32,000 , MPa - 220 30%
Corrosion Resistance Properties of Alloy 825
UNS N08825 is a versatile engineering alloy with resistance to corrosion in acids and alkalis under both oxidizing and reducing conditions. The high nickel content gives the alloy virtual immunity to stress corrosion cracking. The corrosion resistance in various media like sulfuric, phosphoric, nitric and organic acids is good, as well as the corrosion resistance in alkalis or ammoniac, sea water and caustic chloride. The versatility of UNS N08825 is illustrated by its use in nuclear fuel element dissolvers where a variety of corrosive media, e. g. sulfuric and nitric acids and sodium hydroxide, are handled in the same equipment.

Processing Alloy 825

Fabrication Incoloy 825 can be readily hot or cold worked. Hot working should be in the range 870 – 1180°C, finishing at 870 – 980°C. For maximum corrosion resistance hot worked parts should be stabilise annealed before use. The alloy is easier to cold form than stainless steels.
Machinability Machining Alloy 825 should be machined in the annealed temper. As the alloy is prone to work-hardening, low cutting speeds and appropriate feed rates should be used and the tool should be engaged at all times. Sufficient chip depths are important to get below the work-hardened surface layer. The optimum dissipation of heat through the use of large amounts of appropriate, preferably water containing cooling lubricants is crucial for a stable machining process.
Welding: The alloy is readily weldable by the normal processes (GMAW (MIG), GTAW (TIG), SMAW (manual), SAW). The joint must be clean to avoid contamination of the weld pool.
Heat Treatment Incoloy 825 is stabilise annealed at 940°C. The softest structure is obtained at 980°C. Sections heavier than sheet, strip and wire should be quenched to avoid sensitisation.
Hot working UNS N08825 may be hot-worked in the temperature range 1,150 to 900 °C (2,100 to 1,650 °F) with subsequent rapid cooling down in water or by using air. The workpieces should be placed in the furnace heated to hot working temperature in order to heat up. Once the temperature has equalised, a retention time of 60 minutes for each 100 mm (4 in) of workpiece thickness is recommended. After this, the workpieces should be removed immediately and formed during the stated temperature window. If the material temperature falls below the minimum hot working temperature, the workpiece must be reheated. Heat treatment after hot working is recommended in order to achieve optimum properties and corrosion resistance.
Cold working Cold working should be carried out on annealed material. UNS N08825 has a higher work hardening rate than austenitic stainless steels. This must be taken into account during design and selection of forming tools and equipment and during the planning of the forming processes. Intermediate annealing may be necessary at high degrees of cold working deformation. After cold working with more than 15 % of deformation the material should be soft annealed.
Applications Applications of Alloy 825 include chemical processing, pollution control, oil and gas recovery, acid production, pickling operations, nuclear fuel reprocessing, and handling of radioactive wastes.