714 SUMMARY OF CURRENT RESEARCHES RELATING TO 



surfaces when they are brought together under suitable conditions. In 

 a microsectiou of a weld, the crystals along the junction are found to be 

 common to each of the original pieces of metal. The higher the tem- 

 perature at which clean metallic surfaces are in actual contact, the more 

 rapidly do they crystallize together. Upon heating in contact, in hydro- 

 gen, duplicate pieces of steel, welding resulted at as Iowa temperature as 

 800° C. Axial holes were drilled in three steel bars, and closed with 

 steel plugs ; the bars were heated to 800° C. and flattened, then re-heated 

 respectively to 750°, 950°, and 1150° C, and forged into liars of smaller 

 section. The piece forged at 750° C. showed no signs of welding of the 

 artificial cavity, while the bar forged at 950° was partially, and that 

 forged at 1150° C. completely welded. The author discusses the forma- 

 tion of blowholes, of blowhole segregations, and of pipe in steel ingots. 

 It seems certain that blowholes will weld up completely when an ingot 

 is rolled or forged at a temperature of 1000° C. or higher. It is doubt- 

 ful if pipe cavities can be so readily welded, as the surfaces of such 

 cavities are frequently coated with oxide. 



Some Studies of Welds.*— E. F. Law, W. H. Merrett, and W. P. 

 Digby have investigated the strength and the microstructure of steel 

 welded by various processes. A true weld is regarded as involving 

 fusion together of similar or allied metals. Whatever the process used, 

 a more or less sharply defined region of altered structure is produced. 

 Each process develops its own characteristic structural features in this 

 region, so that a microscopical examination of an unannealed weld in- 

 dicates by what process it has been made. Resistance welds and acetylene 

 welds appear to be least, and arc welds most, prone to oxidation. 



Resistance of Steels to Abrasion and to Crushing.j — F. Robin 

 has tested a large number of different steels and cast irons by submitting 

 them to abrasion by emery paper. The test piece, having a surface of 

 given area, was pressed with a given load upon a disc of emery paper 

 rotating at a known speed on a turntable. Usually the loss of weight 

 of the test piece was determined after 1, 2, and 3 minutes' abrasion. 

 Carbon steels show a minimum of resistance to abrasion at about ' 4 p.c. 

 carbon. Steels containing nickel and manganese in high percentages 

 are exceedingly resistant. Another method of testing investigated 

 consists in the determination of the relation between energy of blow 

 and amount of compression in a metal cylinder deformed by the blow of 

 a falling weight. The shock work is the energy of a single blow pro- 

 ducing at a given temperature a crush equal to one-fifth of their depth 

 in normal cylinders at a constant velocity, and is held to characterize 

 the metal tested. The tests were carried out upon a large number of 

 carbon and alloy steels, at temperatures from - 180° to over 1100° C. 

 In connexion with this test, " interstrain," or the hardening resulting 

 from mechanical distortion, was studied. The original paper should be 

 consulted for an account of the great quantity of experimental work 

 performed and the conclusions yielded by it, and for the author's views 

 on the numerous theoretical points raised. 



* Journ. Iron and Steel Inst., lxxxiii. (1911) pp. 103-24 (33 figs.), 

 t Iron and Steel Inst., Carnegie Scholarship Memoirs, ii. (1910) pp. 1-270 

 (94 figs.). 



