Heat treating and inspection of metals Page: 19
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HEAT TREATING AND INSPECTION OF METALS
generally sufficient. The temperatures required for this treatment
are listed in table III.
(c) A final tempering operation is necessary to relieve the harden-
ing strains produced by the previous treatments. This is accom-
plished by heating to the temperatures specified in table III, soaking
until uniformly heated, and cooling in still air. When extreme hard-
ness is desired the temperature should be carefully held to the lower
limit of the range.
TABLE III.-Carburizing heat treatment for steels
SAE steel Carburizing tempera- Grain refinement tem- Hardening temperature drawing tem-
ture ( F.) 1 perature core 2 case 3 perature
1020 . _ 1, 650 to 1, 700 1, 575 to 1, 625 a 1, 400 to 1, 425 350 to 400
2320 -_____ a 1, 600 to 1, 650 1, 500 to 1, 550 b 1, 350 to 1, 400 350 to 400
2512 ...... b 1, 600 to 1, 650 1, 450 to 1, 500 b 1, 300 to 1, 350 300 to 350
3312----- b 1, 600 to 1, 650 1, 425 to 1, 475 b 1, 350 to 1, 400 300 to 350
4615 ..... b1,650to 1,700 1, 450 to 1, 500 b 1, 335 to 1, 400 300 to 400
6115... a1,625to 1,675 1,550tol, 600 a1,450to 1,500 350 to 400
1 Carburize to desired depth of case, including allowance for grinding.
a Cool in air or quench in oil.
b Cool in box to 1,0000 to 1,1000 F. and then in air.
2 Quench in oil. This treatment may be omitted for 1020 steel on low stressed parts.
* Water or brine.
b. Cyaniding.-Steel parts may be surface hardened by heating
while in contact with a cyanide salt, followed by quenching. Only a
thin case is obtained by this method and it is, therefore, seldom used
in connection with airplane construction or repair. Cyaniding is,
however, a rapid and economical method of case hardening and may
be used in some instances for relatively unimportant parts. The
work to be hardened should first be heated to 7500 F., then immersed
in a bath of molten sodium or potassium cyanide from 10 to 15 minutes.
The cyanide bath should be maintained at a temperature of 1,550
to 1,600 F. Immediately after removal from the bath the parts
are quenched in water. The case obtained in this manner is due
principally to the formation of carbides on the surface of the steel.
The use of a closed pot is required for cyaniding as cyanide vapors are
c. Nitriding.-(1) This method of case hardening is advantageous
due to the faot that a harder case is obtained than by carburizing.
Many engine parts such as cylinder barrels, gears, etc., may be treated
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United States. War Department. Heat treating and inspection of metals, book, September 10, 1941; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc96657/m1/21/: accessed July 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.