The Effect Of Tempering On Water-quenched Gages





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

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After Tempering temperature, degrees Centigrade

Thread quenching-----------------------------------------

220 260 300 340 380 420

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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

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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.





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