requenching

Requenching is a heat treatment practice in which a metal, typically steel, is quenched a second time after an initial quench. The second quench may follow a tempering or aging step, or may occur after a preliminary transformation that did not reach the desired microstructure. In some implementations, the material is re-austenitized between quench steps and then quenched again to obtain a refined martensitic structure or to reduce retained austenite.

The main purpose of requenching is to adjust mechanical properties by promoting a more uniform microstructure. It can help improve hardness, wear resistance, and strength, or to reduce uneven transformation in thick sections where the first quench did not complete the desired phase change. Requenching can also be used to relieve certain internal stresses or to correct issues such as hardness gradients.

Practices vary by alloy and geometry. Typical approaches include re-austenitizing the part between quench cycles and using controlled quench media to minimize distortion. Direct second quenching after an initial quench is also used in some processes, but it can increase the risk of cracking, distortion, and residual stresses if not properly controlled.

Requenching is not universally required or standard for all alloys; it is a specialized step used in select heat-treatment workflows, often in tool steels or other alloys where precise control of the martensitic microstructure is critical. Proper process development and testing are essential to determine whether requenching yields the desired properties for a given material and part.