Photomicrography of Iron and Steel. By W. H. Merrett. 1 I 



occurs in a matrix of martensite or a mixture of martensite and 

 ferrite. Fig. 12 shows a variety of troostite in a matrix of martensite. 

 Steels containing troostite are soft ; they are, however, not so soft as 

 steel containing pearlite. In ordinary steel the pearlite develops at 

 about 700° C. Should a specimen be quenched after the formation of 

 this constituent, it will not harden. In practice, steel is generally 

 quenched at nearly 1000° C, which has the effect of converting the 

 whole mass into martensite. 



If the proportion of carbon in a steel be high, say I ' 5 per cent., and 

 if the cooling be rapidly effected in iced brine, another constituent 

 appears, which may be scratched with a hard needle, and to which 

 M. Osmond, who discovered it, has given the name of " austenite," 

 after Sir W. Roberts-Austen, Its general appearance is shown white 

 in fig. 13, magnified 850 diameters. 



Very rapid advance has lately been made in the metallography of 

 iron and steel, and the effects of elements other than carbon on iron 

 have been carefully studied. Mr. J. E. Stead, of Middlesborough, 

 has recently published a most interesting paper on the alloys of iron 

 and pbo.sphorus.* 



Although the metallography of iron and steel was originally of 

 scientific interest only, it has lately become of the greatest commer- 

 cial importance ; as from a suitable photomicrograph one is able almost 

 to read the life-history of a piece of steel, at any rate as regards the 

 thermal treatment it has received. 



The demonstration was illustrated by a number of lantern slides of 

 the structures of iron and steel, a few of which have been reproduced 

 in this Eeport. 



* See this Journal, 1901, pp. 608, 721; 



