ON THE TREATMENT OF STEEL FOR THE CONSTRUCTION OF ORDNANCE. 401 



tons, and its elongation 20 per cent. Anothei- block of gun steel contain- 

 ing rather more carbon, namely -41 per cent., gave the following results. 

 A test piece cut from the block in its original state began to stretch at 

 14 tons per square inch, broke at 32-5 tons, and elongated 23 per cent. 

 The same cut from a thick lamp of the same material which had been 

 tempered in oil resisted 28 tons before permanent stretch, and 43 tons 

 before breaking, with an elongation of IG per cent., thus showing the 

 much greater effect of the tempering process where the proportion of 

 carbon is increased, but showing also that the loss of ductility by the 

 process becomes more considerable. 



It being important to ascertain whether cylinders which have been 

 tempered in oil could be reheated sufficiently for the purpose of shrinking 

 upon a gun, without destroying the eifect of the tempering, a test piece 

 cut from the same tempered lump of this steel was heated in melted zinc 

 to a temperature of 750°, and then allowed to cool naturally in air. Com- 

 paring its resistance with the piece which had not been reheated, it gave 

 25 tons per square inch against 28 tons before stretching, and 40-2 tons 

 against 43 before breaking, but its ductility was increased from 16 per 

 cent, to 20-5 per cent., so that although rendered slightly inferior in 

 strength, it was rendered more ductile and tougher by the reheating. 

 Similar experiments made with steel rather lower in carbon showed that 

 the effect of reheating to this temperature was almost inappreciable either 

 in the way of improvement or the contrary, and no degree of sudden 

 cooling from so low a temperature had any distinct effect. On carryino- 

 the reheating to still higher degrees the effect of the previous tempering 

 gradually diminished, but was not altogether obliterated even when the 

 temperature was raised to the bright red heat at which the steel had been 

 immersed in the oil for the purpose of tempering. The friability of the 

 steel at a welding temperature became more marked as the percentao-e 

 of carbon was increased. Of the many samples I tried the highest m 

 carbon was the block already mentioned, containing 41 per cent, of 

 carbon. This steel, like the milder samples, suffered very little from 

 being merely heated to the welding temperature, provided that while'so 

 heated it was not disturbed by hammering, but it was so friable at that 

 temperature that it broke into a mass of small crumbs under a moderate 

 blow of the hammer. It was remarkable, however, that the same blow 

 of the hammer which detached them from the block united them in a thin 

 cake on the anvil. 



I Whether this friability at a high temperature can be corrected by 



combming other materials with it, is a point upon which my experience 

 casts no light. If it can be so corrected without detriment to the material, 

 the knowledge of how to do it will be an important acquisition to metal- 

 lurgical science. 



Many of my test pieces were taken from rolled steel hoops containino- 

 from -22 to -35 per cent, of carbon, and all of these showed much greater 

 tenacity than was exhibited by test pieces taken from forged blocks of 

 similar material. It is one of the characteristics of mild steel that it is 

 enormously increased both in strength and toughness by being drawn 

 out either by rolling or hammering, but especially by rolling, which is 

 more uniform in its action than hammering. There can be no doubt that 

 the process of rolling steel tyres may be extended to the production 

 of rolled hoops of great width, and the time may not be distant when 

 we may see a realisation of the prediction made many years ago by Sir 

 1882. D X) 



