The purpose of full annealing is similar to that of normalizing, as it aims to reduce hardness, increase ductility, and enhance the material’s homogenization, along with certain metalworking properties such as machinability, formability, and cold workability. The full annealing temperatures depend on the steel’s chemical composition, particularly its carbon content. For hypoeutectoid steels, full annealing temperatures are slightly above the A3 critical temperature, ensuring complete austenization. In the case of hypereutectoid steels, full annealing temperatures are just above the A1 critical line, representing a dual-phase austenite–cementite region.

With full annealing, the steel is subjected to a longer period at a specific temperature (soak time) and undergoes substantially slower cooling compared to normalizing. This process produces a softer structure that is virtually stress-free.

Once the required thermal conditions are met, the steel can be either slowly cooled at a controlled rate or rapidly cooled to a specific elevated temperature and held there for isothermal transformation.

An associated process with full annealing is homogenization, primarily aimed at achieving a homogeneous structure by eliminating alloy segregation. Homogenization is usually performed at higher temperatures than full annealing, creating favorable conditions for diffusion-driven processes needed to homogenize and dissolve carbides. The temperature range for homogenization typically falls between 1000°C and 1150°C.

Due to the extended holding times required for processes like full annealing and homogenization (often spanning many hours), controlled cooling at a low rate, or maintaining the workpiece at an elevated temperature for isothermal transformation, the cost-effectiveness of using induction heaters for these purposes is significantly reduced. As a result, induction heating is rarely employed in these applications. Other heat sources like gas furnaces and resistive furnaces are typically more suitable choices.

However, there are specific applications for long products where induction heating can be effectively utilized. This includes the heat treatment of wires or thin-walled tubular products, such as the “black,” “dull,” and “bright” annealing of stainless steels.

Stainless steel tubing finds use in decorative hardware, food processing, and various applications where a shiny, corrosion-resistant surface is desirable. In this process, stainless steel tubing is heated using electromagnetic induction to temperatures around 1050°C–1150°C and is subsequently passed through a gas quench tunnel filled with a hydrogen–nitrogen atmosphere to prevent surface oxidation and achieve a bright appearance. Safety precautions should be taken, as the gas mixture can become explosive due to the presence of hydrogen in concentrations greater than 4% or so.

In cases where only a nitrogen atmosphere is used, the surface of the tubes will appear dull, and this process is referred to as “dull annealing.” Without a special atmosphere, the tubing’s surface will oxidize, leading to what is often called “black” annealing.

is similar to that of normalizing, as it aims to reduce hardness, increase ductility, and enhance the material’s homogenization, along with certain metalworking properties such as machinability, formability, and cold workability. The full annealing temperatures depend on the steel’s chemical composition, particularly its carbon content. For hypoeutectoid steels, full annealing temperatures are slightly above the A3 critical temperature, ensuring complete austenization. In the case of hypereutectoid steels, full annealing temperatures are just above the A1 critical line, representing a dual-phase austenite–cementite region.

With full annealing, the steel is subjected to a longer period at a specific temperature (soak time) and undergoes substantially slower cooling compared to normalizing. This process produces a softer structure that is virtually stress-free.

Once the required thermal conditions are met, the steel can be either slowly cooled at a controlled rate or rapidly cooled to a specific elevated temperature and held there for isothermal transformation.

Typically, full annealing is carried out in gas or electric furnaces, falling into two basic categories: batch furnaces or continuous furnaces.

An associated process with full annealing is homogenization, primarily aimed at achieving a homogeneous structure by eliminating alloy segregation. Homogenization is usually performed at higher temperatures than full annealing, creating favorable conditions for diffusion-driven processes needed to homogenize and dissolve carbides. The temperature range for homogenization typically falls between 1000°C and 1150°C.

Due to the extended holding times required for processes like full annealing and homogenization (often spanning many hours), controlled cooling at a low rate, or maintaining the workpiece at an elevated temperature for isothermal transformation, the cost-effectiveness of using induction heaters for these purposes is significantly reduced. As a result, induction heating is rarely employed in these applications. Other heat sources like gas furnaces and resistive furnaces are typically more suitable choices.

However, there are specific applications for long products where induction heating can be effectively utilized. This includes the heat treatment of wires or thin-walled tubular products, such as the “black,” “dull,” and “bright” annealing of stainless steels.

Stainless steel tubing finds use in decorative hardware, food processing, and various applications where a shiny, corrosion-resistant surface is desirable. In this process, stainless steel tubing is heated using electromagnetic induction to temperatures around 1050°C–1150°C and is subsequently passed through a gas quench tunnel filled with a hydrogen–nitrogen atmosphere to prevent surface oxidation and achieve a bright appearance. Safety precautions should be taken, as the gas mixture can become explosive due to the presence of hydrogen in concentrations greater than 4% or so.

In cases where only a nitrogen atmosphere is used, the surface of the tubes will appear dull, and this process is referred to as “dull annealing.” Without a special atmosphere, the tubing’s surface will oxidize, leading to what is often called “black” annealing.