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[Chris [Stockport]]

Can anybody help me out with this one? ANNEAL when softening copper (heat to cherry red and cool etc) and aluminium (NOT too hot!!) BUT what about steel? Can it be ANNEALED or just hardened and tempered? (Been in discussion with a German friend who's a jeweller.) Any thoughts welcome. Ta, Chris

[p]

Copper will be softened by annealing, either cooling slowly or plunging in cooling agent - water usually. Steel wil be more maleable if heated and cooled slowly, but will be hardened by plunging, tempering is the process of reducing this hardening to the required point by plunging at predetermined temperature, usually determined by colour change.

[simon]

If I remember correctly from school metal work annealing aluminium is best achieved by covering the piece in acetylene soot and then burning it off with a hot flame. Shows you where you've been and keeps you moving was the theory I believe. Steel you anneal by allowing it to cool slowly with the amount of carbon in the steel dictating how hard it can be tempered. (Lead bright not really at all silver steel to glass hard) Quenching for tempering is usually done in oil and the temper can be measured by the colour you heat it to prior to the quench blue being the hardest.

[MadMike]

Chris, annealing is the softening of metals usually to their softest condition. Annealing copper or aluminium is relatively simple dueto the low temperatures involved and the fact that both are already "soft" materials. Temperatures are controllable by looking at the colour of the material and then quenching. Simples so far. Now we turn to steels and the problem becomes much more complex. For instance the the higher the temperature to which the steel is heated to produce an austenitic structure, the greater the greater the tendency of the dtructure to become lamellar (pearlitic) in cooling.On the other hand the closer the austenitic temperature to the critical temperature, the greater is the tendency of the annealed steel to become spheroidal. Temperature is critical and is deopendent on the carbon conent of the steel. Temperatures between 1000F and 1700F are normal but in narrow tolerance bands depending upon the carbon. Slow cooling is also essential. Sorry but there is no easy answer except that yes steels can be annealed, but not simply I am afraid. I could provide a much more detailed treatise on this if you like, but...... HTH.

[Chris [Stockport]]

Many thanks for the replies. Gave me and my German friend something to try and translate between. I think we've got there! -C