90 SUMMARY OF CURRENT RESEARCHES RELATING TO 



suitably annealed is much the same whatever may he the direction of the 

 polished face of the section. But in rolled or forged steel the constituents 

 are commonly arranged in parallel bands or strings, and the appearance 

 of a microsection accordingly depends upon the direction of the polished 

 face with respect to the directions of flow of the steel during the 

 mechanical working operations. P. Oberhoffer has studied this lamin- 

 ated structure in a large number of boiler plates, structural steels, and 

 other hot-worked shapes. The laminated structure was found to persist 

 after heating to temperatures not excessively high, followed by slow 

 cooling. The origin of such banded structures probably lies in the action 

 of slag-inclusions as nuclei upon which the ferrite crystallizes during 

 cooling through the critical ranges. 



Cold-rolling of Steel.* — H. Haneinann and C. Land have studied 

 the various properties of a steel strip containing 1*2 p.c. carbon at 

 each stage of the manufacturing process, consisting of successive cold- 

 rollings and annealings. Before the first cold-rolling the material 

 consisted structurally of lamellar pearlite and a cementite network. 

 At an early stage in the process the material had become wholly con- 

 verted into granular pearlite, the excess cementite changing into small 

 granules indistinguishable from the eutectoid cementite. Steel in which 

 the carbide is contained in the form of granular pearlite is in the 

 softest possible condition, capable of enduring without permanent injury 

 severe change of form by cold- working, and is thus peculiarly adapted 

 for cold-rolling. By a suitable final hardening or annealing, the granular 

 pearlite may be replaced by a structure having greater strength. 



Annealing of Steel Castings.! — P. Oberhoffer has studied the effect 

 upon the properties of two steel castings, containing respectively ' 23 

 and 0'66 p.c. carbon, of annealing at different temperatures. The 

 gradual replacement of the coarse casting structure by a fine-grained 

 structure as the annealing temperature is raised, is illustrated by a 

 series of photomicrographs. To remove completely the coarse ferrite 

 network of the casting structure, the annealing temperature must not 

 be lower than the temperature of first separation of ferrite. 



Structure of a Broken Axle. J — M. Piichsel describes the micro- 

 structure of a railway-wagon axle, manufactured about twenty years 

 ago, which broke in use. The ferrite and pearlite ran in parallel 

 1 lands, forming a remarkably well-developed coarse, laminated, or 

 banded structure. Numerous slag-inclusions were present in the ferrite. 

 The individual ferrite grains of which the bands consisted were not 

 elongated in the direction of the length of the bands. Such a struc- 

 ture indicates that the axle was rolled at a high temperature and slowly 

 cooled. Annealing at 850° C, followed by cooling at a moderate speed, 

 completely removed the banded structure, the ferrite and pearlite now 

 being well mixed. A similar fine uniform structure was found in an 



*& 



* Stahl und Eisen, xxxiii. (1913) pp. 551-5 (9 figs.). 



t Stahl und Eisen, xxxiii. (1913) pp. 891-6 (22 figs.). 



* Stahl und Eisen, xxxiii. (1913) pp. 1487-9 (5 figs.). 



