. Transactions. -ever, when the surface is slightly polished and then etched, no darkeningresults nor is there left any trace of the pattern developed by material constituting the surface is pure ferrite (Fig. 8a); all thepearlite has been removed to a considerable depth, as is shown inFig. 86, a section of the specimen perpendicular to the polished face,the normal appearance of the material being seen in the lower portion ofthe micrograph. The boundary between the outer, or carbonless, metaland the inner normal material is clearly defined, showing that the changefrom the outer
. Transactions. -ever, when the surface is slightly polished and then etched, no darkeningresults nor is there left any trace of the pattern developed by material constituting the surface is pure ferrite (Fig. 8a); all thepearlite has been removed to a considerable depth, as is shown inFig. 86, a section of the specimen perpendicular to the polished face,the normal appearance of the material being seen in the lower portion ofthe micrograph. The boundary between the outer, or carbonless, metaland the inner normal material is clearly defined, showing that the changefrom the outer zone to the unchanged metal of the interior is very abrupt. »»An alloy of iron and carbon prepared according to the method given by U. of Standards. Sci. Paper 266. HENRY S. RAWDON AND HOWARD SCOTT 423 Fig. 9a illustrates the pattern developed by heat-relief on thepohshed surface by heating above the Ad transformation. The moreclearly defined network, corresponding to the 7 condition, is superimposed. Fig. 7.—Microstrccture of low-carbox steel jdst above the Aci transfor-mation. The polished specimen was heat-etched by heating 30 mix. at 760 ° C. a. Both ferrite and pearlite are clearly shown. X100. b. The boundaries of the ferrite grains extend through the pearlite ISLANDS. X500. upon a less distinct one which shows the characteristic outlines of the acrystals; this is more plainly seen in Fig. 96. The polished specimen inthis instance was etched to reveal its initial structure and then heated for 424 MICROSTRUCTURE OF IRON AND MILD STEEL AT HIGH TEMPERATURES 30 min. at 1000° C, or well above the temperature of the Ac3 roughening of the surface, corresponding to the islands of pearlite
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
