. The Iron and steel magazine. d, but which partly retainscarbide in the metastable condition. This is, in fact, the funda-mental principle of the production of chilled castings. Manganese would favor the tendency to supercooling. It remains still to be explained why the condition corre-sponding to the two phases, iron and graphite, has been acceptedas stable. If white, that is, metastable solidified iron, be heatedto higher temperatures,— for example to red heat,— and if at thesame time, what practically is very hard to carry out, the heatingis so conducted that the carbon content remains as
. The Iron and steel magazine. d, but which partly retainscarbide in the metastable condition. This is, in fact, the funda-mental principle of the production of chilled castings. Manganese would favor the tendency to supercooling. It remains still to be explained why the condition corre-sponding to the two phases, iron and graphite, has been acceptedas stable. If white, that is, metastable solidified iron, be heatedto higher temperatures,— for example to red heat,— and if at thesame time, what practically is very hard to carry out, the heatingis so conducted that the carbon content remains as far as possibleunchanged, a decomposition takes place in the interior of theiron. Carbon separates out in a form which is known to themetallurgist as temper carbon. This kind of carbon can neithermetallographically nor analytically be distinguished from graph-ite. It is extremely closety related to graphite, possibly evenidentical with it. Figure 20 shows an iron originally white, The Constitution of Iroji-Carbon Alloys 47. tree from graphite, in which this separation has taken iron contained, before tempering, percent carbon, and,indeed, in a form other than graphite. After annealing for 108hours,* it contains per cent total carbon, of which a largeproportion was in the form oftemper carbon. Figure 20 showsto the right the dark tem-per carbon (graphite) imbeddedin a light surrounding of some distance from this, lieswell-defined pearlite, and in thisto the left, cementite. The es-sential point to be noted is thatthe temper carbon lies in theneighborhood of the ferrite. Atthe places, therefore, where thestable condition has been reached,the two phases iron and carbonare in contact with each other,and pearlite still remain unchanged next to each other; there,the stable condition has not yet been reached. The occurrenceof the stable condition, therefore, starts from single centers,nuclei, and spreads gradually out from them. This is a signthat th
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Keywords: ., bo, bookcentury1800, bookdecade1890, booksubjectiron, bookyear1898
