Thermal and physical changes accompanying the heating of hardened carbon steels
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730 U. S. BUREAU OF STANDARDS NOTES. [J. F. I. RELATION OF THE HIGH-TEMPERATURE TREATMENT OF HIGH-SPEED STEEL TO SECONDARY HARDENING AND RED HARDNESS.’ By Howard Scott. [ABSTRACT.] THERE has, been more or less mystery attached to certain well- known phenomena connected with the heat treatment of high- speed steel. Anticipating a disappearance of the mystery with the acquirement of sufficient pertinent experimental data, the physical characteristics and the microstructure of a standard type of high- speed steel a,s affected by quenching temperature, tempering tem- perature, and treatment below ordinary temperatures were studied. The experimental results obtained appear to warrant the fol- lowing conclus’ions. : ( I ) Secon,dary hardening necessitates prior partial austenitization produced by the high-temperature treat- ment ; (2) the variations with heat treatment in physical proper- ties and microstructure of high-speed s;teel are analogous to those of hypereutectoid carbon steel with the exception of the micro- structure of hardened but untempered steel ; (3) red hardness is largely a function of the composition of the matrix and is only colmparatively slightly affected by the amount of dissolved car- bide. Three reasons are given for the establis’hed advantages derived fro&m th,e use of the high-temperature heat treatment, namely, increased red hardness, increased initial hardness, and reduced brittleness. THERMAL AND PHYSICAL ‘CHANGES ACCOMPANYING THE HEATING OF HARDENED CARBO’N STEELS.6 By Howard Scott and H. Gretchen Movius. [ABSTRACT.] THERMAL analysis was used here for determining the: thermal ch‘aracteristics of hardened carbon steels below A,. A definite heat evolution, called Act, was observed for a normal rate of heating starting at about 165” C., reaching a maximum at 270~ C. and ending at 290’ C.; the effect on it of the variables-rate of heating, tempering, carbon content, and quenching temperature- was studied. - 4 Scientific Paper No. 395. ‘Scientific Paper No. 396.
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Transcript of Thermal and physical changes accompanying the heating of hardened carbon steels
730 U. S. BUREAU OF STANDARDS NOTES. [J. F. I.
RELATION OF THE HIGH-TEMPERATURE TREATMENT OF HIGH-SPEED STEEL TO SECONDARY HARDENING
AND RED HARDNESS.’
By Howard Scott.
[ABSTRACT.]
THERE has, been more or less mystery attached to certain well- known phenomena connected with the heat treatment of high- speed steel. Anticipating a disappearance of the mystery with the acquirement of sufficient pertinent experimental data, the physical characteristics and the microstructure of a standard type of high- speed steel a,s affected by quenching temperature, tempering tem- perature, and treatment below ordinary temperatures were studied.
The experimental results obtained appear to warrant the fol- lowing conclus’ions. : ( I ) Secon,dary hardening necessitates prior partial austenitization produced by the high-temperature treat- ment ; (2) the variations with heat treatment in physical proper- ties and microstructure of high-speed s;teel are analogous to those of hypereutectoid carbon steel with the exception of the micro- structure of hardened but untempered steel ; (3) red hardness is largely a function of the composition of the matrix and is only colmparatively slightly affected by the amount of dissolved car- bide. Three reasons are given for the establis’hed advantages derived fro&m th,e use of the high-temperature heat treatment, namely, increased red hardness, increased initial hardness, and reduced brittleness.
THERMAL AND PHYSICAL ‘CHANGES ACCOMPANYING THE HEATING OF HARDENED CARBO’N STEELS.6
By Howard Scott and H. Gretchen Movius.
[ABSTRACT.]
THERMAL analysis was used here for determining the: thermal ch‘aracteristics of hardened carbon steels below A,. A definite heat evolution, called Act, was observed for a normal rate of heating starting at about 165” C., reaching a maximum at 270~ C. and ending at 290’ C.; the effect on it of the variables-rate of heating, tempering, carbon content, and quenching temperature- was studied. -
4 Scientific Paper No. 395. ‘Scientific Paper No. 396.
Nov., 19x1.] U. S. BUREAU OF STANDARDS NOTES. 731
It is shown that for a very slow rate of heating this transfor- mation is practically independent of carb,on content, and that it then ends at about 260’ C. This temperature undoubtedly repre- sents the end of the transition of martensite into the troostite of tempering. The transformation is also closely associated with the physical changes accompanying the tempering of hard- ened steel.
A STUDY OF THE RELATION BETWEEN THE BRINELL HARD- NESS AND THE GRAIN SIZE OF ANNEALED
CARBON STEELS.
By Henry S. Rawdon and Emilio Jimeno Gil. [ABSTRACT.]
IN some of the simple alloys a rather definite relation exists between grain size and hardness. A study was’ made of five types of carbon steel in various conditions of grain size to determine whether such a i-elation exists for steels. The variations in grain size were produced by annealing for long periods’ at different tem- peratures and also by low-temperature annealing after a prelimi- nary straining of the metal. Two methods were used for obtain- ing the hardness values, the standard Brine11 apparatus and a small type, designated as the “ micro-Brine11 ” testing set, by which the hardness of individual grains could be measured.
In general there appears to be no definite relation between grain size and Brine11 hardness, except in thme case of a very pro- nounced increase in grain size, which is usually accompanied by a decrease in the hardness.
The general effect of heating steel, i.e., in annealing, is to harden it appreciably, this increase in hardnes,s is noticeable in spite of any sharp drop which may a.ccompany an abrupt change of grain size.
The rate at which steels are cooled, and consequently the struc- tural condition of the hardening constituent, affects the hardness much more than any other factor.
Incidental to the study of the hardness of steels coarsened by annealing after permanent strain, some data were obtained rela- tive to the magnitude of the necessary stress required to cause pronounced grain growth upon annealing such strained metal below the A, transformation tem’uerature.
‘Scientific Paper No. 397.
