Which annealing process is used to reduce internal stresses without reaching the austenite transformation temperature?

The annealing process that is used to reduce internal stresses without reaching the austenite transformation temperature is stress relief annealing. This specific technique involves heating a material, typically steel, to a temperature below its transformation point. The purpose of this process is to relieve residual stresses that may have been introduced during manufacturing processes such as welding, casting, or machining.

By carefully controlling the temperature during stress relief annealing, the material can achieve a more uniform microstructure without altering its phase significantly. This process enhances material performance by increasing ductility and reducing the risk of deformation or failure during subsequent use.

In contrast, sub-critical annealing might not specifically denote a controlled method designed only for stress relief, as it is a broader term that often encompasses any annealing process that occurs below the transformation range. Full annealing typically involves heating a material above the transformation point to achieve a complete phase change and then allowing it to cool slowly, which is not suitable for merely relieving stresses. Temperature controlled annealing might imply an attempt to maintain specific characteristics under controlled conditions, but it does not emphasize the goal of stress relief as clearly as stress relief annealing does.