Isothermal Tempering

During isothermal annealing, you hold the workpiece at a fixed temperature until the structure has transformed. You do this when you want to specifically set certain properties like toughness without unwanted transformations. If you don't hit the temperature or holding time cleanly, you get the wrong structure and the part becomes either too hard or too soft. In practice, this means: put the workpiece in the furnace, bring it to the right temperature, and leave it there until the transformation is complete – don't take it out early. Work by feel and experience values, not by rigid times.