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The Effect Of Tempering On Water-quenched GagesCategory: HARDENING CARBON STEEL FOR TOOLS The following information has been supplied by Automatic and Electric Furnaces, Ltd., 6, Queenstreet, London, S. W.: Two gages of 3/4 in. diameter, 12 threads per inch, were heated in a Wild-Barfield furnace, using the pyroscopic detector, and were quenched in cold water. They were subsequently tempered in a salt bath at various increasing temperatures, the effective diameter of each thread and the scleroscope hardness being measured at each stage. The figures are in 10,000ths of an inch, and indicate the change + or - with reference to the original effective diameter of the gages. The results for the two gages have been averaged. TABLE 24.--CHANGES DUE TO QUENCHING ---------------------------------------------------------------- After Tempering temperature, degrees Centigrade Thread quenching----------------------------------------- 220 260 300 340 380 420 --------------------------------------------------------- 1 +25 +19 +17 +15 +13 +11 +11 2 +18 +12 +11 + 9 + 6 + 5 + 5 3 +12 + 6 + 5 + 3 0 0 0 4 +10 + 4 + 4 + 2 ... 0 - 1 5 + 9 + 4 + 4 + 2 0 0 0 6 + 9 + 4 + 3 + 2 0 0 0 7 +10 + 5 + 5 + 3 + 2 + 1 + 2 8 + 8 + 4 + 3 + 2 0 0 + 1 9 + 9 + 4 + 3 + 2 + 1 + 1 + 1 10 + 9 + 5 + 5 + 3 + 2 + 2 + 2 11 + 7 + 4 + 4 + 2 + 1 + 1 + 1 12 + 9 + 5 + 5 + 5 + 4 + 4 + 3 Scleroscope 80 70 70 62 56 53 52 ---------------------------------------------------------------- Had these gages been formed with a plain cylindrical end projecting in front of the screw, the first two threads would have been prevented from increasing more than the rest. The gages would then have been fairly easily corrected by lapping after tempering at 220 deg.C. Practically no lapping would be required if they were tempered at 340 deg.C. There seems to be no advantage in going to a higher temperature than this. The same degree of hardness could have been obtained with considerably less distortion by quenching directly in fused salt. It is interesting to note that when the swelling after water quenching does not exceed 0.0012 in., practically the whole of it may be recovered by tempering at a sufficiently high temperature, but when the swelling exceeds this amount the steel assumes a permanently strained condition, and at the most only 0.0014 in. can be recovered by tempering. Next: Tempering Colors On Carbon Steels Previous: Tempering Round Dies
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