58 Mr. Gill on softening and hardening Steel. [July, 



Article VIII. 



On softening Steel by heating and quenching it, and on the hard- 

 ening and tempering it at one Operation. By. Thomas Gill, Esq. 



(To the Editors of the Annals of Philosophy.) 



No. 1 1 , Covent Garden Chambers, 

 GENTLEMEN, June 15, 1818. 



I have now the pleasure of communicating for insertion in 

 your Annals, the above two processes on steel ; and which, to 

 artisans in general, may seem to be impossibilities, being so very 

 different to the general practices ; but which, nevertheless, can 

 be readily performed under proper management, and possess 

 very considerable advantages over the ordinary methods. 



It is well known that unless steel be heated to the proper 

 degree, it will not harden on being quenched in water, or other 

 proper fluid ; but it has escaped the general observation, that 

 steel heated rather below the hardening point and quenched will be 

 softened thereby, and in a much superior manner than by the 

 usual methods of annealing it, insomuch that it can be more 

 readily filed, turned, &c. and is entirely free from pins or hard 

 spots ; and as it is not at all liable to be injured by this process, 

 and can be softened thereby in a much shorter time than by 

 annealing it, so it ought to be universally adopted. 



Steel springs are usually hardened and tempered by two 

 distinct operations, being first heated to the proper degree, and 

 hardened by quenching in water, oil, &c. and then tempered, 

 either by rubbing them bright and heating them till they acquire 

 a pale blue or grey colour, or by burning or blazing off the 

 oil, &c. 



It is, however, now found that both operations may be advan- 

 tageously performed at once, in the following manner : 



The steel being heated to the proper degree, is to be plunged 

 into a metallic bath composed of a mixture of lead and tin, such 

 for instance as plumbers' solder, and which is heated by a proper 

 furnace, to the tempering degree, as indicated by a pyrometer 

 or thermometer placed in the bath, when the steel wilt be at once 

 hardened and tempered, and with much less danger of warping or 

 cracking in the process than if treated in the usual way. 



It would be a further improvement to heat the steel in a bath 

 of red-hot lead to the proper degree for hardening, previous to 

 quenching and tempering it in the other metallic bath, as it 

 would thereby be more uniformly heated, and be in less danger 

 of oxidation ; and, indeed, it is an excellent method of heating 

 steel, either for softening it, as in the first described process, or 

 for hardening and tempering it at once, as in the last mentioned 

 one, or even for hardening it in the usual method. 



