THE AGE OF STEEL 



1.50 per cent, of carbon, and about 12 per cent, of 

 manganese. If a small quantity of manganese, that 

 is, i or 2 per cent., is used the steel is very brittle, 

 and becomes more so as greater quantities of the man- 

 ganese are used, up to about 5 per cent. From that 

 point, however, it becomes more ductile as the quan- 

 tity of manganese is increased, until at about 12 per 

 cent, it reaches an ideal state. When used for safes 

 and money vaults this steel has one great advantage 

 over chrome steel it is not affected by heat. By using 

 a blow-pipe and heating a limited area of steel, the 

 burglar is able to "draw the temper" of ordinary steel 

 to a sufficient depth so that he can drill a hole to admit 

 a charge of dynamite; but manganese steel retains its 

 temper under the blow-pipe no matter how long it 

 may be applied. Against attacks of the sledge, how- 

 ever, it is probably inferior to chrome steel. 



Like manganese steel, tungsten steel retains its 

 temper even when heated to high temperatures. For 

 this reason it is used frequently in making tools for 

 metal-lathe work where thick slices of iron are to be 

 cut, as even at red heat such a tool continues to cut 

 off metal chips as readily as when kept at a lower tem- 

 perature. This steel contains from 6 to 10 per cent, 

 of tungsten, a metallic element with which we have 

 previously made acquaintance in our studies of the 

 incandescent lamp. 



[297] 



