How is MONEL 400 Alloy Heat Treated? What are the Temperature and Processes for Heat Treatment and Cold Working?

MONEL 400 alloy, also known as Nickel Alloy N04400, is accurately described as a nickel-copper alloy primarily composed of nickel and copper. Let's follow the ASTM alloy guidelines to delve into its heat treatment process!

• Annealing Heat Treatment: Generally, the annealing heat treatment of MONEL 400 alloy should be carried out in the temperature range of 700 to 900°C (1300 to 1650°F), with a recommended temperature of approximately 825°C (1510°F). Rapid air cooling or water quenching is recommended to achieve better corrosion resistance. For example, a batch of hot-rolled plates from Japan was designed to be heat-treated at 850°C and quenched in water for 6 minutes. The temperature and holding time are crucial for the subsequent grain size, so these parameters need to be carefully considered when determining the annealing parameters.
• Hot Working: MONEL 400 alloy can be hot worked in the temperature range of 1200 to 800°C (2200 to 1470°F), but only light hot working can be performed below 925°C (1700°F). Hot bending should be carried out between 1200 and 1000°C (2200 to 1830°F). For heating, the workpiece can be placed in the furnace at the operating temperature. After the furnace returns to temperature, the workpiece should be held at this temperature for 60 minutes per 100 mm (4 inches) of thickness. At the end of this period, it should be removed immediately and worked within the aforementioned temperature range. If the metal temperature drops below the minimum working temperature, it must be reheated.

It is recommended to anneal the alloy after hot working to achieve better performance and ensure excellent corrosion resistance.

• Cold Working: Cold working should be performed on annealed material. The work-hardening rate of MONEL 400 alloy is slightly higher than that of carbon steel, so forming equipment must be adjusted accordingly. Intermediate annealing may be required for heavy cold forming. Stress relief or annealing is needed after more than 5% cold work.

In some cases, the enhanced strength from cold working can be utilized. However, in such cases, stress in the alloy should be relieved by heating between 550 and 650°C (1020 to 1200°F). Cold rolling is sometimes used to improve mechanical properties. Under conditions where stress corrosion cracking may occur, such as in mercury or moist acidic hydrofluoric acid vapor, subsequent stress relief is recommended.

It is important to note that regardless of the type of heat treatment, the material should be placed in the heat treatment furnace and held at the heating operating temperature.