FIG. 75.—Peg withdrawn after cooling to 760°C. The increased amount of free ferrite arranges itself about the crystals as envelopes.
FIG. 76.-Peg withdrawn after cooling to 740°C.
FIG. 77.—Peg withdrawn after cooling to 670°C. (magnified 800 diameters). Just at this moment the lamination of pearlite, which now occupied its original area, was taking place. In some parts the lamination was perfect, in other parts the iron and iron-carbide were still dissolved in each other.
The center piece Fig. 65 represents a block of steel weighing about 25 lb. The central hole accommodated a thermo-couple which was attached to an autographic recorder. The curve is a copy of the temperature record during heating and cooling. Into the holes in the side of the block small pegs of overheated mild steel were inserted. One peg was withdrawn and quenched at each of the temperatures indicated by the numbered arrows, and after suitable preparation these pegs were photographed in order to show the changes in structure taking place during heating and cooling operations. The illustrations here reproduced are selected from those photographs with the object of presenting pictorially the changes involved in the refining of overheated steel or steel castings. Figures 66 to 79 with their captions show much that is of value to steel users.
FIG. 78.—Any peg withdrawn after 670°C. on cooling (magnified 100 diameters).