Austenitization holding time
The duration required at annealing temperatures to ensure complete carbide dissolution and homogeneous carbon distribution in the face-centered cubic lattice.
Austenitizing means: Bring the part completely to annealing or hardening temperature until the structure is fully transformed. Only then does the carbon dissolve properly in the lattice and you get a homogeneous distribution. If you anneal too short, carbides remain, which later causes cracks or an uneven hardening pattern. Too long annealing makes the grain coarse, the part becomes brittle and not tough either. In practice: Get to temperature, then give a proper hold time until the part is heated through. The right time depends on the material and the cross-section, there is no one-size-fits-all recipe. Stick to the material manufacturer's specs or the heat treatment instruction for that steel.