Metal Heat Treatment-Anhui Zhuoxu New Material Technology Co., Ltd.

Metal Heat Treatment

Bright annealing, powder metallurgy sintering, and carburizing—processes aimed at preventing oxidation and enhancing surface quality—commonly utilize nitrogen with a purity of 99.9% or higher. As an inert, non-oxidizing, non-decarburizing, colorless, and odorless gas, nitrogen serves as the most versatile protective atmosphere in heat treatment applications. Its core functions revolve around preventing oxidation and decarburization, and facilitating bright quenching.

These Benefits Can Be Categorized Into Six Key Areas

Bright Annealing / Bright Quenching (Most Common Application): When steel is heated to high temperatures, exposure to air causes rusting, oxidation, surface decarburization, and insufficient hardness. By introducing nitrogen to displace the air, workpieces emerge from the furnace with a bright, silvery-white finish, free of oxide scale. This completely eliminates surface decarburization while guaranteeing the required hardness and wear resistance. It is an essential process for the annealing of molds, bearing steels, stainless steels, and steel strips.

Carburizing and Carbonitriding Protection: Nitrogen is used to dilute the furnace atmosphere, thereby stabilizing the carbon potential and ensuring a uniform carburized layer. This results in consistent workpiece hardness, minimizes internal oxidation, and enhances the overall metallographic quality.

Tempering and Solution Treatment: For processes such as stainless steel solution treatment and high-temperature tempering, nitrogen purging prevents intergranular corrosion and stabilizes the metallurgical structure, ensuring the material remains free of discoloration or blackening.

Gas Quenching (Common in Vacuum Furnaces): Following vacuum heating, high-pressure nitrogen is rapidly introduced to facilitate rapid cooling. This method minimizes deformation, ensures uniform hardness, and serves as an effective alternative to oil quenching, leaving the workpieces clean and free of oil residue.

Furnace Purging and Atmosphere Displacement: During furnace startup, shutdown, or material loading/unloading, nitrogen is used to purge the air from the furnace chamber. This prevents explosions, protects workpieces from high-temperature oxidative damage, and—through the use of a nitrogen curtain at the furnace door—effectively seals the chamber against the ingress of ambient air.

Heat Treatment of Stainless Steel, Copper, and Aluminum: Since copper and aluminum are highly susceptible to oxidation and blackening at high temperatures, nitrogen protection is critical. This ensures that finished products possess a mirror-like bright finish, eliminating the need for subsequent acid pickling or mechanical polishing. Nitrogen provides high-temperature oxidation prevention, safeguards against decarburization during heating, controls deformation during gas cooling, and prevents combustion hazards within the furnace.

Common Purity Levels: For general heat treatment applications, 99.9% purity is typically used; for precision molds and stainless steel, 99.99% high-purity nitrogen is recommended.

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