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THE HARDENING TRANSFORMATION IN MANGANESE — —«.^ STEELS ?"
"Ij^y H. Scott and J. G. Hoop
f roa'iT j : .'*" чмая
Abstract * "АУЧНС-ТЬХ" ^чеоИАя /iosuacx j БИВЛИОТЕНА onn»
77ze hardening transformation, Ar", though it occurs at a comparatively Ion' temperature, is shown to be a vital factor in the quenching of steel. The temperature at which it starts was evaluated in steels containing from 4.5 to 12.0 per cent manganese and from 0.2 to 1.0 per cent carbon under conditions which assured all the carbon being brought into and retained in solid solution.
With the data available, an equivalence relation between manganese and carbon with respect to their effects on the temperature of Ar" was established. Carbon in solid solution was shown to have twelve times the effect of manganese within certain composition limits.
The temperature of Ar" in iron-carbon alloys was estimated by extrapolation from the general relation established for high manganese steels. Our results agree with the best published data when Ar" starts near 250 degrees Cent, and are probably quite close to the actual location of the hardening transformation in iron-carbon alloys cooled from above the critical range at rates above the critical cooling rate.
EVERY steel hardened by a quench which produces martensite undergoes the hardening transformation, Ar". at a temperature considerably below that of Ar,. The conditions which exist during this transformation determine in a large measure the success of the treatment. Thus it has been shown1 that an oil-hardening steel of simple shape will crack or not depending on the cooling rate through Ar", that is, below 400 degrees Cent. (750 degrees Fahr.).
An" explanation for the critical importance of the cooling rate
1H. Scott, "Origin of Quenching Cracks," Bureau of Standards Scientific Paper No. 513, 1925.
The authors are associated with the Research Laboratories of the Westing-house Electric and Manufacturing Co., East Pittsburgh, Pa. The senior author is a member, of the society. Manuscript received June 22, 1932.