Case harden is a term used to describe the process of hardening the surface of metal by heating and then cooling it rapidly. There are several antonyms for case harden, which represent the opposite of the process. These include temper, anneal, soften and malleabilize. Tempering involves heating and then slowly cooling a metal to increase its overall toughness and reduce brittleness. Annealing, on the other hand, is a process of heating and then cooling a metal to relieve stress and make it more ductile. Softening is the process of reducing the hardness of the metal through heating and controlled cooling. Malleabilizing is the process of making metal more ductile and easy to shape through controlled heating and cooling.