Introduction to GH2747 High-Temperature Alloy

GH2747 is an age-strengthened deformation high-temperature alloy from the Fe-Ni-Cr-Al system, with a maximum service temperature of up to 1,300°C. Due to its excellent high-temperature strength, high-temperature oxidation resistance, corrosion resistance, and microstructural stability, as well as its ease of forming and welding, it is widely used in the manufacturing of high-temperature oxidation-resistant components in aerospace, nuclear power, petrochemical, metallurgical, and other fields. Currently, there is limited research on GH2747 high-temperature alloy both domestically and internationally, primarily focused on seamless tube manufacturing, microstructure, and performance studies. However, there are no reported studies on the effects of heat treatment temperature and holding time on the microstructure and hardness of GH2747 alloy. This paper investigates the impact of heat treatment regimes on the metallographic structure and hardness of GH2747 cold-rolled seamless tubes produced using industrial production equipment, aiming to provide a theoretical basis for establishing industrial heat treatment specifications for this alloy.

The GH2747 alloy was smelted in a 12-ton vacuum induction furnace and cast into a Φ360 mm × 2,800 mm ingot. It was then refined using the Φ430 mm electroslag remelting process, forged into a 200 mm octagonal billet, and further radial forged into a Φ70 mm round tube billet. Subsequent processes included peeling, cutting, and drilling center holes, followed by hot piercing to produce a rough tube of Φ70 mm × 7 mm. The specific chemical composition is shown in Table 1. The hot-pierced GH2747 rough tube was cold-rolled in two passes to a finished tube size of Φ25 mm × 3 mm, followed by degreasing.

Chemical composition of GH2747 is shown in the table

At a heat treatment temperature of 1,000°C, the grains of the GH2747 alloy are fine and uniform. As the heat treatment temperature increases, the grains gradually grow. When the heat treatment temperature is between 1,000°C and 1,050°C, the grains of the GH2747 alloy remain relatively uniform. Beyond 1,050°C, individual grains grow significantly.

Under different holding times, the average grain size of the GH2747 alloy follows the same trend with increasing heat treatment temperature, with grains gradually growing as the temperature rises. In the temperature range of 1,000°C to 1,075°C, grain growth in the GH2747 alloy is slow. Beyond 1,075°C, grain growth accelerates slightly. The apparent activation energy for grain boundary migration in the GH2747 alloy is 234.9 kJ/mol.

At different heat treatment temperatures, the average grain size of the GH2747 alloy increases with prolonged holding time. After a holding time exceeding 20 minutes, the rate of grain growth slows. The variation of average grain size with holding time follows Beck's formula. In the temperature range of 1,000°C to 1,075°C, the kinetic time exponent η for the GH2747 alloy is approximately 0.39. It decreases when the temperature exceeds 1,075°C. Material introduction.

Various specifications of plates, bars, strips, wires, discs, ring blanks, and ring forgings are available. Bars are supplied in forged or rolled condition, with surfaces ground or turned; discs and ring blanks are supplied in as-forged condition; rings are supplied in solution-treated condition; plates are supplied after solution treatment, alkali pickling, leveling, and edge trimming; strips are delivered after cold rolling, solution treatment, and descaling; wires are supplied in solution-pickled coil or straight form, or in solution-treated straight finely ground condition.