Ultra Alloy 825

General characteristics

Outokumpu Ultra Alloy 825 (W.-Nr. 2.4858, UNS N08825,
ISO NW8825) is a titanium stabilized austenitic nickel base alloy with an addition of copper.

Typical applications


  • Components in sour gas service
  • Offshore oil and gas piping systems
  • Equipment in petroleum refineries
  • Heating coils
  • Heat exchangers
  • Tanks
  • Chemical processing equipment


Product forms, available sizes and finishes


Product typeFinishesThicknessWidth
Cold rolled coil and sheet2E1,51-4,50≤ 1500
Quarto plateHot rolled white8,00-40,00≤ 2700
Chemical composition

The typical chemical composition for this grade is given in the table below, together with composition limits given for this grade according to different standards. The required standard will be fully met as specified on the order.

TypicalUltra Alloy 8250.0100.823.039.03.2Si:0.35 Cu:1.7 Ti Al:0.1
Mechanical properties

The mechanical properties of the available products are given in the table below.


StandardGradeRp0.2Rp1.0RmElongationImpact strengthRockwellHBHV
Product type: Cold rolled coil and sheet
Typical (thickness 1 mm)Ultra Alloy 825280620

Outokumpu Ultra Alloy 825 shows good mechanical properties from moderately high temperatures down to cryogenic temperatures. Outokumpu Ultra Alloy 825 shall not be used at temperatures above approximately 540 °C as ductility and impact strength become lowered due to changes in the microstructure. Outokumpu Ultra Alloy 825 is normally not used where creep rupture properties are design factors.

Corrosion resistance

Uniform corrosion
Outokumpu Ultra Alloy 825 shows very good resistance in many acids, e.g. sulphuric acid (see Fig. 1), phosphoric acid, nitric acid as well as organic acids. Alloying with e.g. molybdenum and copper improves the corrosion resistance in reducing acids. Outokumpu Ultra Alloy 825 also shows good resistance in alkaline environments like sodium and potassium hydroxide solutions.


Pitting and crevice corrosion
The resistance to pitting and crevice corrosion is higher than for e.g. Supra 316L/4404 types of stainless steel, but does not reach the level of e.g. Ultra 254 SMO. Typical values in Table 4.


Stress corrosion cracking
The high nickel content of Outokumpu Ultra Alloy 825 contributes to the very high resistance to stress corrosion cracking, both chloride induced as well as in alkaline environments. This is illustrated by the fact that it is expected to pass over 24 hours without cracking when tested according to the very aggressive ASTM G36 (boiling 45% MgCl2).
Outokumpu Ultra Alloy 825 also has excellent resistance to sulphide
stress cracking. In accordance with ISO 15156-3 (NACE MR0175)solution annealed and cold worked Ultra Alloy 825 is acceptable for use for any component or equipment up to 232 °C in sour environments, with no limits on chloride concentration and in situ pH, providing that the partial pressure of hydrogen sulphide (pH2S) does not exceed 2 bar (30 psi). If the temperature does not exceed 132 °C, the material is acceptable for use without restriction on partial pressure.


Intergranular corrosion
Outokumpu Ultra Alloy 825 is stabilized with titanium which in combination with the low carbon content improves the resistance to intergranular corrosion.

Pitting corrosion resistanceCrevice corrosion resistance

PRE Pitting Resistant Equivalent calculated using the formula: PRE = %Cr + 3.3 x %Mo + 16 x %N
CPT Corrosion Pitting Temperature as measured in the Avesta Cell (ASTM G 150), in a 1M NaCl solution (35,000 ppm or mg/l chloride ions).
CCT Critical Crevice Corrosion Temperature is the critical crevice corrosion temperature which is obtained by laboratory tests according to ASTM G 48 Method F



Physical properties



DensityModulus of elasticityThermal exp. at 100 °CThermal conductivityThermal capacityElectrical resistanceMagnetizable

*) Austenitic stainless steel grades may be magnetizable to a certain degree after cold deformation, e.g. in temper rolled condition.


The fabricability of Outokumpu Ultra Alloy 825 is similar to other types of nickel base alloys.


Outokumpu Ultra Alloy 825 has good ductility and can be formed using conventional methods.
Heat treatment
Post fabrication annealing is done at 950°C followed by rapid air cooling or water quenching.


Conventional techniques can be used also with Outokumpu
Ultra Alloy 825. The material work hardens during machining.


Outokumpu Ultra Alloy 825 is readily weldable with conventional welding methods such as:

  • Shielded metal arc welding (SMAW, MMA)
  • Gas tungsten arc welding (GTAW, TIG)
  • Gas metal arc welding (GMAW, MIG/MAG)
  • Submerged Arc Welding (SAW)

Preheating before welding is not necessary.


Outokumpu Ultra Alloy 825 can be welded using matching filler. For e.g. SMAW, covered electrodes of the type 2.4621 or 2.4652 can be used.


Standards & approvals

Outokumpu Ultra Alloy 825 is approved for pressure vessels operating at temperatures up to 538°C, according to ASME Boiler & Pressure Vessel Code, Sections I, III, VIII, IX, Code cases 1936, N-188-1. Material data in Section IID. Some material standards are shown in the table below