Other treatments

Sub-Zero Treatment. Sometimes known as Cryogenic Treatment or metal freezing. This involves freezing components down to temperatures as low as -195°C. with certain materials this can be advantageous as part of the tempering process. The process is also used to aid shrink fitting of components when heating of the larger component is restricted.

Martempering or Marquenching. This is the term used to describe the treatment of a through hardening steel in which the cooling is interrupted just above the martensite transformation temperature, and held until the surface and the core of the component are at the same temperature, the cooling is then resumed. As the surface and the core transform at the same time, the residual stress is lower which in turn minimises distortion and the risk of cracking. It is a more expensive process than conventional quenching and may not be possible on certain metals.

Austempering. This is the term used to describe the treatment of a through hardening ferrous metal in which the cooling is interrupted above the martensite transformation temperature and held until the transformation is completed at that temperature. This produces a bainitic structure which when compared to conventional quenching results in a softer, more ductile component with distortion minimised which usually requires no further tempering treatments.

This process has been applied very successfully to hardenable cast irons often referred to as Austempered Ductile Iron (ADI).

Precipitation Hardening or Age Hardening. There are certain alloys [commonly some types of stainless steels and copper-based alloys] that will through harden by this method. The treatment typically involves a “solution treatment” which is carried out at high temperature followed by one or more “ageing” Treatments at progressively lower temperatures to achieve the correct hardness [note. The material only hardens after the age hardening treatment]

This material is usually available in the normalised state, [lowest price but requires full heat treatment] the solution treated state, [only requires ageing treatment so distortion is minimised] and the over aged condition [no further heat treatment required but the metal is soft enough for machining operations]. Care should be taken in specifying the ageing condition as this can often effect the corrosion resistance.

Shrink Fitting. This is the term used when one component is fixed to another by means of an interference fit. It usually involves heating one component and/or cooling the other before assembling them. The Wallwork group have extensive experience in this field & can give advice in fit tolerance etc.