In many cases the design engineer requires that only part of the component is hardened.
E.g. not threads or bores.
Holt’s specialise in techniques to protect selective areas of components from carburisation and thus from hardening.
Flame and induction hardening are used on medium carbon steels to deliver selective hardening to specific areas of the component’s geometry
Stopping Off – The terminology used to describe protecting areas of a component to prevent Carburising or Nitriding in that area
Although for many case depths, and with current grain-growth-inhibited steels, refining is often considered as not being necessary.
However, because grain growth occurs at the elevated temperatures necessary for carburising, and where the carburising cycles are long (to produce particularly deep cases), or the component would benefit from a finer grain size, then core (grain) refining, can be specified.
Refining increases the deformation strength of the steel at the micro level – (yield strength at the macro level)
Holts offer the same range of furnace types and sizes for refining, as those used for carburising