rJ13] on Recent Advances in Scientific Steel Metallurgy G05 



centuries, this material has naturally had its name branded on inferior 

 kinds of steel. Indeed, bars of steel up to 6 inches in diameter have 

 been sold as " shear steel," at 18.s. per cwt., the price of the raw 

 material from which shear steel is manufactured. Probably a bar 

 1^ inch in diameter marks the advisable hmit of size for genuine 

 shear steel, and its average market price is about 45s. per cwt. 



The year 1740 marked for Sheffield, and indeed for the world, 

 the beginning of an epoch of great metallurgical importance. Benja- 

 min Huntsman, a well-known clock-maker of Doncaster, found that 

 shear steel, on account of its sometimes varying temper and of its 

 weld-lines, often presented uneven hardness and exasperating flaws 

 when made into clock springs. He consequently determined to 

 make a steel even in texture and free from weld flaws. He experi- 

 mented successfully and worked out a method for the production of 

 sound steel ingots by the fluid or crucible process, and so founded in 

 Sheffield an industry destined to become world-wide, and which soon 

 extended the fame of Sheffield steel throughout the civilized world. 

 The next slide shows a composition typical of crucible cast steel. 

 It is less pure than shear steel, but sounder, being free from weld lines. 

 It is said that the famous American General Sherman when asked to 

 " spare the good Indians," replied that the only good Indians he had 

 ever met were dead Indians. Be this as it may, it is certain that 

 no steel can be good unless it is properly " killed," or in other words 

 " dead melted." The slide on the screen (Fig. 2) shows sections of two 

 crucible steel ingots of identical composition and weight, when poured 

 in a " lively " and in a " killed " condition. Ignoring the " pipe " or 

 central contraction cavity, the killed steel is quite solid, whilst the 

 unkilled metal is riddled from end to end with gas cavities or 

 " blowholes " containing under pressure hydrogen, carbonic oxide and 

 nitrogen gases, evolved in the plastic steel during solidification, and 

 thus rendering the ingot commercially worthless. The sound, and 

 hence apparently much smaller, ingot has been " killed " by the 

 presence of a trace (say O'Ol per cent) of metallic aluminium. 

 The scientific explanation of this, the most remarkable phenomenon in 

 the whole range of steel metallurgy, may be found in text-books or in 

 reports of metallurgical lectures, but the present lecturer must con- 

 fess that he is no nearer a convincing solution of this problem than 

 when he began his researches twenty-five years ago. 



It is next necessary to correlate the chemical and mierographic 

 analyses of the plain carbon steel upon which the world depended 

 for its cutting implements from the time of Homer to 1870. 



The slide on the screen shows the structure of pure Swedish iron, 

 contaminated with a little slag. Ignoring this, the mass consists of 

 white allotrimorphic crystals of iron with optically black boundaries. 

 The next slide (Fig. 3) is a micrograph of nearly pure iron, containing 

 about 0*4 per cent of carbon. Nearly half the mass consists of the 

 dark-etching compound constituent pearlite. The next slide (Fig. 4) 



