398 REPOKT— 1882. 



Ooi the Treatment of Steel for the Construction of Ordnance, and 

 other purposes. By Sir William Armstrong, G.B., F.R.S. 



[A communication ordered by the General Committee to be printed in extenso 



among the Keports.] 



The improvement whicli of late years has been effected in the manufacture 

 of steel, and the control which has been attained over the quality produced, 

 now seem to justify its exclusive employment in the construction of ord- 

 nance. We have, therefore, to consider what are the conditions under 

 which it can be most favourably used for that and other purposes. 



There is at present much want of a proper definition of steel. The 

 term was formerly confined to iron containing a much higher proportion 

 of combined carbon than is to be found in the so-called mild steels of the 

 present day. Where steel ends in the downward scale of carbonisation, 

 and where iron begins, it is impossible to say, for not even wrought iron 

 is absolutely free from carbon. The chief distinction between iron and 

 steel now seems to lie in the process of manufacture — steel being operated 

 upon in a state of fusion, while iron is dealt with in a state of agglutination. 

 But, even in the mild state, steel, as thus defined, contains more carbon 

 than is generally to be found in wrought iron, and this excess, small as it 

 is, appears to exercise a very important influence upon its qualities. These 

 qualities have been very distinctly brought out in some investigations 

 I have recently had occasion to make on the welding, tempering, drawing, 

 and annealing of steel, and as the results possess a general interest inde- 

 pendently of gun-making I shall now place the substance of them before 

 this Section. 



First, as to the adaptation of steel for welding. As a matter of every- 

 day pi'actice, we know that steel very low in carbon is capable of welding, 

 and it has frequently been maintained that, without departing from the 

 system of constructing ordnance known as the ' coil system,' great ad- 

 vantage Avould be realised by substituting mild steel for wrought iron in 

 the makino- of welded coils. Our distinguished President, Dr. Siemens, 

 who has taken such a leading part in the modern development of steel 

 manufacture, and whose knowledge of the metallurgy of the subject is not 

 surpassed by that of any other person, has held this opinion, and a few 

 years ago he supplied to my firm a sample of mild steel specially prepared 

 for this purpose. It was very low in carbon, containing only about yV^^i 

 per cent. A test piece cut from the bar as it came from the maker 

 showed the limit of elasticity, or point at which permanent stretch com- 

 menced to be 13'5 tons per square inch, being not much greater than that 

 of wrouo-ht iron ; and it broke at 23'3 tons, showing that its ultimate 

 strength was also very similar to that of iron, but its ductility was so 

 great that it stretched to the extent of 37'5 per cent, on a length of two 

 inches before breaking. A similar test piece tempered in oil had its 

 elastic limit raised to 24 tons per square inch, and it broke at 286 tons 

 per square inch, while its ductility remained nearly the same as before, 

 the elongation being 36 per cent, instead of 37'5. It will be perceived, 

 therefore, that the material was of a very fine quality, and if the results 

 attained with the tempered specimen could have been realised in a welded 

 coil, its superiority over wi'ought iron would have been very marked 



