[Illustration: FIG. 68.--A portion of 66 magnified 200 diameters to show that the dark (pearlite) areas are laminated.] [Illustration: FIG. 69.--A portion of 67 magnified 200 diameters, showing that pearlite areas are no longer laminated and providing reason for observed hardness.] [Illustration FIG. 70.--Peg withdrawn at 780 deg.C. (magnified 25 diameters), showing inter-diffusion of transformed pearlite and ferrite areas.] [Illustration: FIG. 71.--Peg withdrawn at 800 deg.C. (magnified 25 diameters), showing inter-diffusion so far advanced that the original outline of the crystals is now only faintly suggested.] [Illustration: FIG. 72.--Peg withdrawn at 850 deg.C. (magnified 100 diameters) after inter-diffusion was completed. Note the regular outlines and the small size of the crystals as compared with 67.] [Illustration: FIG. 73.--To facilitate comparison 67 was enlarged to the same magnification as 62, and the one superimposed on the other. The single large crystal occupied as much space as 8,000 of the smaller ones.] [Illustration: FIG. 74.--The peg withdrawn on cooling at 800 deg.C. (magnified 100 diameters) shows the first reappearance of free ferrite. All pegs withdrawn at higher temperatures were like Fig. 72.] [Illustration: FIG. 75.--Peg withdrawn after cooling to 760 deg.C. The increased amount of free ferrite arranges itself about the crystals as envelopes.] [Illustration: FIG. 76.-Peg withdrawn after cooling to 740 deg.C.] [Illustration: FIG. 77.--Peg withdrawn after cooling to 670 deg.C. (magnified 800 diameters).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.] [Illustration: FIG. 78.--Any peg withdrawn after 670 deg.C. on cooling (magnified 100 diameters).] [Illustration: FIG. 79.--Structure of overheated steel before (left) and after refining (right).] CHAPTER IX HARDENING CARBON STEEL FOR TOOLS For years the toolmaker had full sway in regard to make of steel wanted for shop tools, he generally made his own designs, hardened, tempered, ground and usually set up the machine where it was to be used and tested it. Most of us remember the toolmaker during the sewing machine period when interchangeable tools were beginning to find their way; rather cautiously at first. The bicycle era was the real beginning of tool making from a manufacturing standpoint, when interchangeable tools for rapid production were called for and toolmakers were in great demand. Even then, jigs, and fixtures were of the toolmaker's own design, who practically built every part of it from start to finish.