Nov 21 2012
Topics Covered
IntroductionChemical CompositionPhysical PropertiesOther DesignationsFabrication and Heat Treatment Machinability Forming Welding Heat Treatment Cold Working AnnealingApplications
Introduction
Super alloys or high performance alloys are used in environments with very high temperature above 540ºC (1000ºF) where deformation resistance and high surface stability are chiefly required. They have good oxidation and creep resistance. Cobalt-base, nickel-base and iron-base alloys are the three major types of super alloys. The iron-base super alloys are generally wrought alloys provided with stainless steel technology. Nickel-base and cobalt-base super alloys may be cast or wrought based on its composition or application. Super alloys can be generally forged, rolled to sheet or produced in different shapes. Highly alloyed compositions are formed as castings. They can be strengthened using hardening techniques like work hardening, solid-solution hardening and precipitation hardening.
The following section explains in detail about Inconel 722™, which is a nickel-chromium alloy with high corrosion resistance at high temperature.
Chemical Composition
The following table shows the chemical composition of Inconel 722™.
| Element |
Content (%) |
| Carbon, C |
0.08 max |
| Silicon, Si |
0.07 max |
| Sulfur, S |
0.01 max |
| Chromium, Cr |
14 - 17 |
| Iron, Fe |
5 - 9 |
| Titanium, Ti |
2 - 2.75 |
| Manganese, Mn |
1 max |
| Copper, Cu |
0.5 max |
| Aluminum, Al |
0.4 - 1 |
| Nickel, Ni |
Remainder |
Physical Properties
The physical properties of Inconel 722™ are given in the following table.
| Properties |
Metric |
Imperial |
| Density |
8.23 g/cm³ |
0.297 lb/in³ |
| Melting point |
1399ºC |
2550ºF |
Other Designations
Other designations that are equivalent to Inconel 722™ include the following:
- AMS 5541
- AMS 5714
- GE B50T1233
Fabrication and Heat Treatment
Machinability
Inconel 722™ can be machined using conventional techniques employed for iron based alloys. High-speed operations like milling, grinding or turning can be performed using water-base coolants. Heavy lubricants are recommended for operations such as boring, broaching, tapping or drilling. Heavy duty machining tools and equipment can be used prior to cutting in order to reduce chattering or work-hardening of the alloy.
Forming
Inconel 722™ can be formed by conventional means. This alloy can be cold formed using heavy-duty lubricants.
Welding
Welding of Inconel 722™ is performed through commonly used welding techniques like gas tungsten arc welding, shielded metal-arc welding, metal-arc welding and submerged-arc welding. However, an alloy filler metal that suits this alloy should be used.
Heat Treatment
Inconel 722™ is heat treated at 982ºC (1800ºF). The alloy is age-hardened at 760ºC (1400ºF) and then furnace cooled at 621ºC (1150ºF).
Cold Working
Inconel 722™ can be cold worked using standard tooling methods. As plain carbon steels have an ability to produce galling, they are not preferred for forming this alloy. Galling can be minimized with the help of soft die materials.
Annealing
Inconel 722™ can be annealed at 982°C (1800°F) and then rapidly cooled.
Applications
Inconel 722™ is widely used for manufacturing gas turbine structural components like turbine section frames.