Applications and smelting of superalloy A286

I. Overview

The American standard superalloy A286 is an iron-chromium-nickel-based high-temperature alloy, developed through comprehensive strengthening by adding molybdenum, titanium, aluminum, vanadium, and trace amounts of boron. It is equivalent to the domestic grade GH2132 and the French grade ZbNCT25. Depending on the standard to which A286 belongs, there will be certain differences in chemical composition, mechanical properties, and heat treatment regimes.

1. Chemical Composition (Refer to standard SAE J467b) 

2. Mechanical Properties (Refer to standard SAE J467b)

In the solution-treated state, the microstructure of A286 alloy consists of a γ-phase austenite matrix. It is strengthened by the precipitation of the intermetallic compound γ' phase Ni3(Ti, Al) during aging. After solution and aging treatment, it possesses good comprehensive properties, such as high yield strength, good hot hardness, and high creep strength

Mechanical Properties after Heat Treatment per Other Common Standards

4. Heat Treatment Regimes (Heat treatment regimes corresponding to each standard)

II. Application Fields

A286 possesses high yield strength, stress rupture strength, and creep strength below 650°C, as well as good processing plasticity and welding performance. It is suitable for manufacturing components working long-term below 650°C:

1. High-temperature load-bearing parts for aero-engines Such as turbine disks, compressor disks, and rotor blades.

2. Fasteners Such as various bolts, screws, self-locking nuts, aviation rivets, etc. Common material standards for A286 high-temperature alloy used in fasteners include AMS 5726/5731/5732/5734/5737/5853 (Bar and Wire standards). The main types of these products are concentrated in 900MPa class nuts, 1100MPa class aviation HB series bolts, 1300MPa class NAS series high-strength bolts, and test mandrels.

III. Melting Methods 

Most high-quality high-temperature alloys and corrosion-resistant alloy specialty materials both domestically and internationally are not produced using a single process. Instead, they are smelted using duplex or triplex methods, namely Vacuum Induction Melting + Electro-Slag Remelting (VIM+ESR) or Vacuum Induction Melting + Vacuum Arc Remelting (VIM+VAR).

Currently, domestic A286 alloy high-temperature material uses the VIM+VAR process for smelting to improve and guarantee the purity of the alloy, making the alloy's thermal strength and long-term service performance better.

1. Vacuum Induction Melting (VIM) This is a method of smelting in vacuum conditions using electromagnetic induction to generate eddy currents within the metal conductor to heat the charge. VIM provides maximum control over chemical composition and prevents the molten liquid from contacting hydrogen, oxygen, and nitrogen in the atmosphere. Electromagnetic stirring not only homogenizes the melt but also continuously brings reactants to the interface between the melt and the vacuum, thereby facilitating subsequent refining reactions. The volatilization and precipitation of gas content and non-metallic inclusions can greatly improve the mechanical properties of most high-temperature alloys. The VIM furnace is important smelting equipment for the production of nickel-based high-temperature alloys, corrosion-resistant alloys, and other special alloy materials. In particular, for alloys containing large amounts of reactive elements like aluminum and titanium, vacuum induction melting must be used.