670 SUMMARY OF CUEKENT RESEARCHES RELATING TO 



Hardening and Tempering of Iron and Steel. * — E. Maurer gives 

 an account, previously published elsewhere, of his work on this sub- 

 ject, and adds lengthy and important conclusions drawn by F. Osmond. 

 By quenching from a sufficiently high temperature y-iron may be 

 produced in hypo-eutectic as well as in hyper-eutectic steel. Cold 

 working may also produce a small proportion of y-iron. No causal 

 relation exists between carbon (as hardening carbon), and hardness of 

 steel. The increase of electrical resistance, due to quenching, appears 

 to be a measurement of the amount of carbon which has gone into 

 solution, and the curve connecting electrical resistance, a function of 

 the hardening carbon, with temperature of re-heating of quenched 

 steels, does not follow the hardness curve. Carbon appears to remain 

 in solution because of the y-iron present in martensite. The letting 

 down of quenched steels proceeds in four distinct stages : — (1) from 

 the ordinary temperature to 150° C. ; (2) 150-300° C. ; (3) 300-450° C. ; 

 (4) 450° C. to the recalescence point. For the complete theory of 

 hardening, founded by Osmond on the facts observed by Maurer and 

 others, the original should be consulted. 



Electrolytic Iron.j — A. Midler lias obtained a considerable quantity 

 of electrolytic iron, containing 0*03-0 '05 p.c. fixed impurities and 

 small amounts of hydrogen and nitrogen, and has studied its thermal 

 and other properties. Microscopic examination showed that the iron 

 was deposited in a laminated form and contained numerous blowholes 

 and mechanical inclusions. With high magnification, systems of lines 

 radiating from points were observed. This star-like structure appeared 

 to be related to the crystalline structure of the iron. Several fusions of 

 the iron, in a magnesia crucible, heated in a vacuum electric resistance 

 furnace, were required to drive off hydrogen and nitrogen. The critical 

 points on heating were found at 917° C. and 765-774° C, and on 

 cooling at 894° C. and 766-759° C. Other critical points were found 

 in hydrogen-containing samples, the most marked being at 1210° C. 



Iron-phosphorus System.f — F. Gercke gives an equilibrium diagram, 

 obtained by thermal and microscopical methods, for the range to 22 p.c. 

 phosphorus. Phosphorus is completely soluble in solid iron up to 1 • 7 p.c. 

 From 1 - 7 to 10 ■ 2 p.c. aeutectic line is found at 980° C. The eutectic 

 solidification-point may, however, be lowered to 880° C. by supercooling. 

 The eutectic iron-phosphide of iron contains 10'2 p.c. phosphorus. 



Iron-phosphorus-carbon System.§— P. Goerens and W. Dobbelstein 

 conclude, from a study of sixteen alloys of different carbon and phosphorus 

 content, that, as regards phenomena. of solidification, this system may 

 be considered as a ternary system, the components of which are iron, 

 carbide of iron, Fe 3 C, and phosphide of iron, Fe 3 P. The ternary eutectic 

 solidifies at 953°C, and has the composition C 1 • 90 P 6 • 89 Fe 91 * 15 p.c. 

 The equilibrium diagram is given. Metallographic methods were found 



* Me'tallurgie, vi. (1909) pp. 33-52 (64 figs.). See also Rev. de Metallurgie, v. 

 (1908) pp. 711-50 ; and this Journal, 1908 p. 784. 

 t Tom. cit., pp. 145-60 (15 figs.), 

 t Up. cit., v. (1908) pp. 004 -9 (14 figs.). § Tom. cit., pp. 561-6 (14 figs.) 



