68 MODERN SCIENCE READER 



tures. At temperatures above Ar 3 we have the " gamma " 

 iron of Osmond, non-magnetic and a solvent for both ele- 

 mental carbon and iron carbide. Between the Ar 3 and Ar 2 

 temperatures we have iron existing in its "beta" condi- 

 tion, non-magnetic but not a solvent for free or combined 

 carbon. Below Ar 3 iron is in its "alpha" condition, mag- 

 netic but not a solvent for free carbon, but possibly a slight 

 solvent for combined carbon. While some metallurgists 

 do not accept this explanation of the significance of the 

 critical temperatures and ranges, all concede that they do 

 occur, and that other elements added to iron carbon alloys 

 change, obliterate, or modify the temperature ranges, and it 

 is just on account of this that different steels require differ- 

 ent temperatures for forging, annealing and hardening. 



So much for the nature of alloy steels, and now a few 

 suggestions as to their treatment and a few words as to the 

 various kinds of alloys. The constitution of these products, 

 chemical and physical, for generations remained unknown 

 and a matter of speculation. Tremendous progress has 

 been made of late years in clearing up a few of the obscure 

 points. 



The first commercial alloy steel, at least the first to make 

 a great name for itself, was Mushet's air hardening tool 

 steel. The next alloys to attract attention were of the 

 structural types, and may be said to have had a public 

 introduction when Riley presented a paper to the Iron and 

 Steel Institute of Great Britain upon iron and nickel. 

 Shortly afterward Hadfield's famous manganese steel was 

 proclaimed and later he has produced many valuable prod- 

 ucts, especially in the line of armor and projectile steels. 

 Along with the making of the new products has proceeded 

 the study of their properties and methods of heat treat- 

 ment. To-day a host of devotees, skilled in the science of 

 heat treatment, apply their knowledge to the manufacture 

 of tools, automobile parts, and machinery to produce re- 

 sults never dreamed of a generation ago. 



The principal types of alloy steels are those used (1) for 



