STRENGTH OF STEEL. 369 



HADFIELD'S UNHAMMERED STEEL CASTINGS. 



HADFIELD'S FORGED CAST STEEL. 



192. Effects of Working Iron and Steel at a Blue 

 Heat. In the accompanying table are some results 

 obtained by Mr. Stromeyer from tests of samples of 

 Siemens-Martin steel. It was pointed out by the author 

 of the paper from which these results are taken that it is 

 usually held that steel may be safely worked at a proper 

 red heat or cold, but that the effect of working the steel 

 at a "blue" or, more properly speaking, " black " heat 

 that is to say, a high temperature which is short of render- 

 ing the metal incandescent gives rise to effects veiy 

 Z2 



