TPT September 2014

Furnaces & heat treatment

No one who has ever stood close to a roaring fire, however well contained, will need convincing that absolute control of the blaze for heating purposes would be a heavy assignment. Yet the literature on furnaces and heat treatment insists on the primacy of that control. Warnings abound of the metallurgical problems that can be confidently expected from the smallest inaccuracy as to temperature or timing. Even with a

perfectly functioning furnace, complex heating cycles designed to optimise mechanical properties can all too easily slip into inducing more or less than what was wanted. Annealing, case hardening, precipitation strengthening, tempering, quenching: each imposes a separate set of heating and cooling requirements. An alloy whose constituents have different melting points presents its own challenge. So does a tube needing to be treated for maximum hardness- minimum brittleness.