MATERIALS AND THE STRENGTH OF MATERIALS 45 



70. Cast steel. The term cast steel, as usually applied 

 to the material used in the construction of gears, etc., is 

 cast iron which has been deprived^ erf some of its carbon 

 before bejng~c'astV'~ 



7T ' MtlA*ft nd Bessemer steel. It is from this material 

 that agricultural machinery is largely constructed. The 

 hardness and stiffness of Bessemer steel varies and de- 

 pends largely upon the carbon conten^. Steel with a high 

 per cent ot carbon (0.17 per cent) is spoken of as a high- 

 carbon steel, and "steel with a low per cent (0.09 per cent) 

 low-carbon steel. Bessemer steel is difficult to weld. 



72. Wrought iron. Wrought iron is nearly pure iron, 

 and is not as strong nor as stiff as mild steel, but can be 

 welded with greater ease. 



73. Tool steel is a high-carbon steel made by carbon- 

 izing wrought iron, and owing to the carbon content may 

 be hardened by heating and suddenly cooling. Tool steel 

 is used for all places where cutting edges are needed. 



FIG. 27 DRAWING ILLUSTRATING THE CONSTRUCTION OF SOFT-CENTER 



STEEL 



74. Soft-center steel, used in tillage machinery, is made 

 up of a layer of soft steel with a layer of high-carbon 

 steel on each side. The high-carbon steel may be made 

 glass hard, yet the soft center will support the surface 

 and prevent breakage. In making soft-center steel, a slab 

 of high-carbon steel is welded to each side of a soft steel 



