358 STI;F.N<;TH OF STKI.L. 



(6) The Bessemer basic process, in which the con- 

 verter is provided with a basic lining, which allows of the 

 use of pig iron containing a moderate percentage of 

 phosphorus, which is not possible in the ordinary Bessemer 

 process. 



(c) The Siemens-Martin process, in which scrap 

 wrought iron is fused at a high temperature in a bath of 

 pig iron, the proportions being such that the resultant 

 percentage of carbon is that of a soft steel. 



('/) The Siemens process, in which a quantity of rich 

 haematite ore is added to the bath of molten pig, so as to 

 effect the decarburising of the cast iron. 



These two latter processes are sometimes modified by 

 the use of a basic lining to the furnace, in place of the acid 

 lining usually employed, so as to allow of the use of 

 phosphoric pig. 



No definite line of demarcation can- be laid down 

 between hard and mild steels, the one merging imper- 

 ceptibly into the other. The following may, however, be 

 taken as the most characteristic qualities of the two 

 kinds : 



HARD STEEL. MILD STEEL. 



Percentage of carbon, 6^0 Percentage of carbon, 1'5 



to 1*5. Tensile strength to 0*1. Tensile and crushing 



and crushing strength high ; strength lower ; soft and 



ductility low ; property of very ductile ; without the 



hardening and tempering ; property of hardening or 



working requires consider- being tempered ; requires 



able care as compared with less care in working than 



mild steel. does hard steel, but more 



than wrought iron. 



Typical load-strain diagrams for steel in tension and 

 compression are given on Figs. 178 and 179. 



Mr. Skelton* gives the percentage of carbon in the 

 harder kinds of crucible cast steel as follows : 



* " Economies of Iron and Steel," Skelton. 



