710 



STEEL 



which is removable for renewal, is fitted with fire- 

 clay cylinders, erf, cd, erf, erf, and each cylinder ia 

 perforated with several holes i to j inch in dhi- 

 meter. It U thus riddled with sixty to a hundred 

 holes, according to its size. These perforations 



communicate by 



means of an air- 

 chamber, c, e, c, r, 

 with a powerful 

 blowing- machine. 

 The whole converter 

 is mounted on an 

 axis, t, and may be 

 thereby turned as 

 required. 



The lining is first 

 made red-hot by 

 liurning coal within. 

 When thus prepared 

 ready for charging, 

 the converter is 

 turned on the axis, 

 i, so that the line, </. 

 shall be horizontal. 

 Molten pig-iron is 

 then poured in at the 

 mouth, a, and thus 

 tig. 3. it forms a pool lying 



in the belly of the 



converter below the line, ef. The blast i now 

 turned on, and the converter turned over to the 

 position shown in the diagram, the melted metal 

 standing over the hundred open holes. It cannot, 

 however, run down these, as the blast of air 

 rushes upwards with much greater force tliiin 

 that of the downward gravitation of the metal. 

 The streams of air tear through the molten metal, 

 and a huge flame roars furiously from the mouth 

 of the converter. With this flame brilliant cas- 

 cades of coruscating sparks are belched forth 

 at irregular intervals, and the dazzling sprav 

 as it dashes against the wall of the flame-shaft 

 rebounds with redoubled splendour. The blast 

 still roars on monotonously, and the flame steadily 

 increases in size and brilliancy, attaining its maxi- 

 mum at about the end of ten minutes. It con- 

 tinues thus for five or ten minutes longer, then the 

 flame contracts. This indicates that the carlion is 

 becoming exhausted, and that the iron, no longer 

 protected by it, is Mgianing to burn. The con- 

 verter is now turned to the position in which it 

 was charged, ami then the melted spiegeleisen is 

 poured into it. A violent ebullition occurs immedi- 

 ately this mixes with the metal that has lieen 

 blown, and a great waving blue flame of burning 

 carlmnic oxide silently pours out of the mouth of 

 the converter. 



Why this violent agitation, and whence conies 

 this great out|M>uring of gas? The writer studied 

 these questions experimentally when the Bessemer 

 process was young, ami found that the carbon is 

 not all himu'il mil, as was then supposed. There 

 remained from J |H?rcent. to ^ per cent, according 

 to the prolongation of the blowing, and liesides this 

 there was a considerable quantity of black particles 

 of oxide of iron in the Mown metal In-fore the 

 spiegeleisen was added, but after this addition 

 tlicy disappeared. These facts answer the ques- 

 tions. The carl >on of the spicgeleisen reduces the 

 black oxide by combining with its oxygen, nnd this 

 combination with o\ygen produces the carbonic 

 oxide. The manganese assist*, for much of it dis- 

 appears from the metallic product, am) is found in 

 the liquid cinder (or 'slag ) combined with oxygen 

 and sinca. The blown metal, before the addition of 

 the spiegelcisen, is ' rotten ; ' it breaks under the 

 hammer whether hot or cold. If overblown it 

 crumble* like sandstone. 



One of the most remarkable phenomena of the 

 Bessemer process is the intense heat to which the 

 metal is subjected. It far exceeds that obtained 

 in any other melting furnace. At first glance this 

 may appear strange, as nothing but cold air is 

 applied to the melted metal. But this metal is 

 pig-iron containing silicon and carbon. Both of 

 these are effective fuels when heated and supplied 

 with oxygen. The manganese adds a little. In 

 an ordinary charge of six tons of average material 

 these fuel substances amount to about 8 cut. 

 They are all burned in the course of alioul twenty 

 minutes, not outside a melting-pot, but within or 

 amidst the melted metal itself ; and thus the heat 

 of this extraordinary amount of combustion in so 

 small a space is rendered exceptionally effective. 

 After the spiegeleisen is all added and well admixed 

 by the agitation it produces, the liquid steel is 

 poured into ingot moulds of suitable sixes accord- 

 ing to its purpose, and these are wrought by ham- 

 mering, rolling, &c. as required. 



Owing to the phosphorus contained in ordinary 

 Bessemer steel, it will rarely (tear as much as 1 per 

 cent, of carbon without becoming worthlessly 

 brittle, and therefore only mild or low carbon steel 

 is made from it for purposes already stated. Messrs 

 Thomas and Gilchnst have succeeded in removing 

 the most of this residual phosphorus by lining the 

 converter with a basic material, a refractory sub- 

 stance in which lime and magnesia preponderate. 

 These bases eagerly combine with phosphoric acid 

 at high temperatures, and by their predisposing 

 affinities assist the phosphorus in combining \\itii 

 the oxvgen of the blast to become the phosphoric 

 acid which they demand. The phosphates of lime 

 and magnesia thus obtained are valuable manures. 

 The practical value of the basic process depends 

 mainly on its rendering impure pig-iron available. 



The 'Siemens-Martin process is now competing 

 very effectively with the Bessemer process. It 

 consists essentially in first obtaining a bath of 

 melted pig-iron of high quality, and then adding 

 to this pieces of wronght-iron scrap or Bessemer 

 scrap, such as crop ends of rails, shearings of plates, 

 &c. These, though practically infusible in large 

 quantities by themselves, become dissolved or fused 

 in such a bath if added gradually. To the bath of 

 molten metal thus obtained spiegeleisen or ferro- 

 manganese is added to supply the required carbon 

 and to otherwise act as already described in the 

 Bessemer converter. The result is tested by small 

 ladle samples, ami when it is of the desired quality 

 a portion is ran off, leaving sufficient bath for the 

 continuation of the process. 



It is evident that here a high degree of purity is 

 attainable by selection ot the scrap, which may ]>< 

 of high quality wrought -iron from which the 

 impurities nave "been removed by puddling. Very 

 fine samples of ' homogeneous metal ' have thus been 

 obtained, resembling wrought-iron in softness and 

 toughness, with some degree of the high temieity 

 -(steel. Where qualities like t hose of ordinary 

 I'.essemer metal are required, this process supplies 

 an economical method of melting up and utilising 

 sui-h materials as old Bessemer rails, i\c. 



T>III/H-I /;/;/. -The special property upon which 

 the great value of steel depends is that of 

 being capable of acquiring various degrees of hard- 

 ness. These are olitained by what is commonly 

 called 'tempering,' which really includes to 

 processes (1) hardening and (2) tempering pro- 

 perly so called. If a piece of steel containing 

 i percent, of carbon and upwards is made red-hot 

 and then suddenly plunged into cold water, or 

 otherwise rapidly cooled, it becomes hardened in 

 proportion to the quantity of carlion it contains. 

 In this condition it is of very little use, as it 

 becomes brittle in proportion to its hardness; but 



