PROCEEDINGS OF THE SOCIETY. 363 



8. Medium Carbon Steel. — R. No. : 970. Analysis : c.c. • 53 p.c, 



Mn 0-89 p.c. Treatment: Annealed. Mag.: x 100. 



Deeply- etched specimen. The background is pearlite not well 

 resolved. Surrounding it are membranes of ferrite. 



Eef. : " Metallography" (Sauveur), p. 124, fig. 140. 



9. Medium Carbon Steel. — R.No.: 977. Analysis: c.c. 0*53 p.c, 



Mn • 89 p.c. Treatment : Quenched 820° C. and reheated to 600° C. 

 Mag. : x 100. 



This is a quenched and tempered specimen in which the structure, 

 though resembling the foregoing, is more compact. This has been 

 tempered at a higher temperature than usual, with the result that the 

 effects of hardening have been greatly modified. 



Ref, : "Metallography" (Sauveur), p. 239 et seq. 



10. Saturated Carbon Steel. — R. No. : 2198. Analysis : c.c. • 96 p.c, 



Mn. 0*36 p.c. Treatment: Annealed. Mag. : x 100. 



This is practically entirely pearlite. Small indications of free 

 cementite can be found here and there. At this carbon content 

 (0*89 p.c. accurately) is the boundary between hypo-eutectoid steel 

 (less than 0*89 p.c. C.) and hyper-eutectoid (more than 0*89 p.c. C). 



Ref. : "Metallography" (Sauveur), p. 127, fig. 146. 



11. Saturated Carbon Steel.— i?. No. : 2199. Analysis : c.c. • 96 p.c, 



Mn 0-36 p.c. Treatment : Quenched 800' C. Mag. : x ,100. 



The treatment has resulted in the formation of martensite. A 

 general idea of the structure can be obtained at this temperature, but 

 higher magnification (some 300 diameters) is needed to resolve the 

 martensite. 



Ref. : " Metallography " (Desch), pp. 47 and 225. 



12. Saturated Carbon Steel.— i^. No. : 2200. Analysis : cc 96 p.c, 



Mn 0-36 p.c Treatment : Quenched <soo° C, tempered 400° C. 

 Mag. : x 100. 



The tempering treatment has relaxed the strain present in the 

 quenched specimen. The theory of tempering is beyond the present 

 purpose. A treatise on the subject will give imformation as to the 

 tempering of steels of varying carbon content. 



Ref : " Metallography " (Sauveur), p. 242. 



13. Supersaturated Carbon Seeel. — R. No. : 2195. Analysis: c.c. 1-41 



p.c, Mn 0*38 p.c. Treatment: Annealed. Mag.: x 100. 



Small membranes of cementite surround the pearlitic areas. The 

 above magnification gives a good idea of the general structure. Higher 

 magnification will resolve the aggregate, though the structure is fine- 

 grained. 



Ref. : " Value of Science in the Smithy and Forge " (Cathcart), 

 p. 83, fig. 37. 



