Super Alloy VLX825 (UNS N08825)

Topics Covered

Introduction
Chemical Composition
Physical Properties
Other Designations
Fabrication and Heat Treatment
     Machinability
     Forming
     Welding
     Forging
     Hot Working
     Cold Working
     Annealing
Applications

Introduction

Super alloys have the ability to function at very high temperatures and mechanical stress, and also where high surface stability is required. They have good creep and oxidation resistance, and can be produced in a variety of shapes. They can be strengthened by solid-solution hardening, work hardening, and precipitation hardening.

Super alloy VLX825 is an austenitic nickel-iron-chromium alloy with other alloying elements in small quantities to improve its resistance to chemical corrosion.

The following sections will discuss in detail about super alloy VLX825.

Chemical Composition

The chemical composition of super alloy VLX825 is outlined in the following table.

Element Content (%)
Nickel, Ni 38 - 46
Chromium, Cr 19.5 - 23.5
Manganese, Mn 1 max
Molybdenum, Mo 2.5 - 3.5
Silicon, Si 0.5 max
Copper, Cu 1.5 - 3
Aluminum, Al 0.2 max
Titanium, Ti 0.6 - 1.2
Carbon, C 0.05 max
Sulfur, S 0.03 max
Phosphorus, P 0.03 max
Iron, Fe Remainder

Physical Properties

The physical properties of super alloy VLX825 are tabulated below.

Properties Metric Imperial
Density 8.13 g/cm3 0.294 lb/in3
Melting point 1385°C 2525°F

Other Designations

Equivalent materials to super alloy VLX825 are provided below:

  • ASTM B163
  • ASTM B423
  • ASTM B424
  • ASTM B425
  • ASTM B564
  • ASTM B704
  • ASTM B705
  • DIN 2.4858

Fabrication and Heat Treatment

Machinability

Super alloy VLX825 can be machined using the common processes applied to iron based alloys. This alloy does work-harden during machining and displays higher strength and "gumminess" unlike steels. It is recommended that heavy duty machining equipment and tooling should be used to reduce chatter or work-hardening of the alloy.

Any commercial coolants can be used during the machining operations; however water-based coolants are recommended for high-speed operations such as milling, turning, or grinding. Similarly, heavy lubricants are ideal for tapping, broaching, drilling, or boring.

Forming

Super alloy VLX825 can be formed using any of the conventional methods as it is very ductile. Powerful equipment is required to perform forming operations as this alloy is stronger than regular steel. It is recommended that heavy-duty lubricants be used while performing cold forming. It is important to clean all traces of lubricant after forming.

Welding

Welding of super alloy VLX825 can be performed using all the traditional welding methods. Matching alloy filler metal should be used. In case that is not available, it is advised that the nearest alloy closest to the chemical composition be used. The weld beads should be slightly convex, and preheating is not required. Surfaces to be welded have to be clean and free from oil, paint or crayon marking.

Forging

Forging should be performed in the temperature range of 1093-982°C (2000-1800°F). A final annealing at 954°C (1750°F) is required to regain optimum corrosion properties.

Hot Working

Hot working can be performed on this alloy; however the temperature should be maintained lesser than 926°C (1700°F) so as to provide the alloy with optimum resistance.

Cold Working

Super alloy VLX825 can be cold formed using all the standard tools except for plain carbon tool steels as they produce galling.

Annealing

Super alloy VLX825 can be annealed at 954°C (1750°F) and then rapidly air cooled.

Applications

Super alloy VLX825 is used in the following application areas:

  • Chemical process equipment
  • Pickling
  • Acid production piping and vessels.

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