March 13, 1913] 



NATURE 



47 



found that hardenite was thermally very unstable, and 

 that its cutting powers were greatly limited by the 

 tact that the heat of friction in turning operations 



caused the hardenite to revert largely to relatively 

 soft pearlite at a blue heat, say, 300 C. This pro- 

 perty naturally limited the operations of engineers as 

 i" speed, as to traverse, and as to depth 

 ut cut, and consequi nth, as to the cost 

 and rate of output of all the 1 ngines and 

 appliances necessan modern 



civilisation. 



(A temp ring diagram wis then ex- 

 plained in which the black areas show 

 the evolution of the latent heat of 

 hardening, and. consequently the trans- 

 formation of the quartz-like hardenite to 

 soft pearlite. This change at about 

 250 (_'. ai quires a marked increase in 

 velocity which reaches a maximum at 

 about 300 C. Here the soft pearlite 

 becomes the predominant partner, and 

 the cutting power of the ma-., has 

 practically vanished.) 



About the year 1870 marked the first 

 beginnings of an epoch in cutting-steel 

 metallurgy, which may be called the 

 tungsten-chrome era. Robert Forrester 

 Mushet, at the Clyde Works, Sheffield, 

 began to manufacture on a considerable 

 scale his " self-hardening steel." Mushet 

 had practically discovered that when 

 carbon steel was alloyed with a large 

 percentage of tungsten, it, when cooled 

 from a yellow heat in a draught of air, 

 was not only sufficiently hardened, but, 

 owing to the fortifying action of the 

 tungsten on the carbon, the hardenite 

 was thermally considerably more stable 

 than that of plain carbon steel. 



It is probable that in Mushet's 

 early steels the " letting-down " point 



dge 



learly completed. Temperature 

 about 730" C. 

 , hardenite. Laminated 



IG. 3. — Palem 



NO. 2263, VOL. 91] 



Trdnsformat 

 normal pear] 



half completed. Temperature about Transformation beginning. Temperature 



729° C. about 728 C. 



Dark border*, tro^stitic pearliti. ^CarbonVS? per cent. Magnifiedjjabout 450 diameter 



