116 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Stead, probably the result of prolonged heating between 600° and 700° C\ 

 In micro-sections taken from a strip annealed at <Sli5° C.^thick bands 

 were observed in the ferrite grains. The bands in any one grain were- 

 parallel, and appeared to have been attacked by the etching solution 

 more strongly than the remainder of the grain. 



Magnetic Changes in Steel.* — H. M. Boylston describes a labora- 

 tory experiment for illustrating the changes in magnetic properties 

 occurring at the thermal critical points in steel. A drilled test-piece, 

 within which is the hot junction of a thermo-couple, is supported just 

 below an electromagnet, and is heated by blast lamps. The critical 

 point is indicated by the test-piece beginning or ceasing to be attracted 

 by the magnet, on cooling or heating. 



Hard Spots in Steel Castings. f — A. P. Scott found that a hard 

 spot in a roll casting consisted of an envelope of metal containing 

 12 p.c. manganese, 1*8 p.c. carbon, sharply differentiated from the 

 steel and surrounding a cavity. Manganese had been added to the 

 molten steel in the ladle only in the form of 80 p.c. ferromanganese. 

 From the results of a number of experiments, in which molten steel was 

 poured into small moulds containing small pyramids of ferromanganese, 

 the author concludes that ferromanganese, when added to molten steel r 

 first melts and then gradually absorbs iron, and probably gas also, fvom 

 the surrounding metal. Complete diffusion does not take place till the 

 liquid manganese alloy has been very considerably diluted. Solidifica- 

 tion of a globule of the manganese alloy results in the formation of a 

 hard spot. 



Methods of obtaining Cooling Curves } — G. K. Burgess gives an 

 outline of the various methods which have been developed for obtaining 

 cooling curves, and briefly describes the apparatus employed. Only those 

 methods of measuring temperature which depend on the use of thermo- 

 couples of the platinum metals are considered. An analytical discussion 

 concludes the paper, and leads to the same result as the examination 

 of the experimental methods : that the most certain and complete data 

 may be obtained by combining temperature-time observations with those 

 given by the differential method. 



Recalescence Curves. § — W. Rosenhain discusses the methods of 

 observing recalescence phenomena, and gives examples of heating and 

 cooling curves obtained by the " time- temperature " and the " differ- 

 ential " methods. The " inverse-rate " and " derived differential " 

 methods of plotting are explained. The author considers that the 

 differential method of obtaining cooling curves is eminently satisfactory r 

 and has important practical advantages over the " inverse-rate" method. 

 The critical point at about 600° C., found by Roberts-Austen in iron, 

 and by Carpenter and Keeling in iron-carbon alloys, is attributed to the 

 presence of crystalline silica in the furnace walls. The author has 

 found a recalescence in crystalline silica at about 580° C. 



* Electrochem. and Met. Industrry, pp. 273-4 (2 figs.). 



t Tom. cit., pp. 281-6, 323-6 (11 figs.). 



% Tom. cit., pp. 366-71, 403-5 (11 figs.). 



§ Proc. Phvs. Soc, xxi. (1908) pp. 180-208 (18 figs.). 



