A heat treatment apparatus includes: a heat treatment chamber that performs heating treatment for a treatment object thereinside; and a thermal insulator disposed inside the heat treatment chamber and surrounding a receiving area for the treatment object. The heat treatment chamber includes a side wall portion and a lid portion configured to be attachable to and detachable from the side wall portion. The thermal insulator includes a ceiling disposed on the inside of the lid portion. The ceiling includes a thermal insulator lid that is at least part of the ceiling and is united to the lid portion.

Multiple temperature-control process for stators (7) and rotors of electric motors and components consisting of materials with different magnetic properties by means of a triplex furnace (1) for the quick, efficient, and uniform heating-up of preferably tubular components such as stators (7), wherein the magnetic parts of a component are primarily heated up by means of induction and at the same time non-magnetic parts of the same component are primarily heated up by means of infrared radiation, and at the same time and subsequently secondary heating takes place by means of convection, in particular by passive heating elements (10), which serves for finely adjusting the target temperature and for maintaining it.

The invention relates to a method for thermally treating chromium steels, in particular high-alloy chromium-x-steels, by gas nitriding, comprising the following process steps: (A) heating a previously hardened component consisting of a chromium steel under a nitrogen atmosphere from an ambient temperature (t.sub.U) to its material-specific pre-oxidation temperature (T.sub.V) for performing a pre-oxidation step; (B) performing at least one tempering step by adding a nitride process gas to the nitrogen atmosphere around the component; (C) further heating the component to its material-specific tempering temperature (t.sub.A) and maintaining it for at least one hour; (D) cooling the component to its material-specific nitriding temperature (t.sub.N) for gas nitriding the component; (E) further cooling the component to the ambient temperature (t.sub.U).