1(3 
MR. J. MUIR ON THE TEMPERIN(^ OF IRON 
Table showing the Tempering of Steel from the condition as supjDhed. 
Condition of the material. 
Primary yield-point. 
Extension at yield- 
points. 
“ Step.” 
A. 
As supplied. 
36-i tons/sri. inch 
0"-16 on 4 inches 
11 tons sq. inch. 
B. 
Annealed at 600^ C. 
36 
C. 
„ 650° „ . . 
334 
0"-16 
94 
U. 
700° „ . . 
3U 
0"-15 
9 
E. 
„ 730° „ . . 
284 
0"-09 
8 
F. 
„ 780° „ . . 
24 
0"-07 
7 
There is thus a relation between the yielding at the yield-point and the step by 
which the yield-point is raised in consequence of recovery from overstrain. This 
step does not depend on the actual extension which the material receives, for it 
was shown in the author’s paper on “ Recovery from Overstrain that a specimen 
could be stretched by any amount (by increasing the overstraining load to any extent) 
without altering the step by which the yield-point was raised aljove the previous 
maximum stress. The amount by which the yield-point is raised after restoration of 
elasticity, and the extension which occui's just at a yield-j^oiiit, are thus definite 
properties of the material—properties which can be altered, at least in some cases, by 
thermal treatment. 
In the experiments which have just been described the specimens were only kept 
for a few minutes at the annealing temperatures, and the times taken to heat up and 
to cool down were in all cases practically the same. As it was thought probable 
that a prolonged exposure to any temperature would have a greater effect than 
a short exposure to the same temperature, the following experiment was tried:— 
A sj^ecimen of the same mateiial as was used to obtain Diagram 3 was raised 
to 700° C., slowl}^ cooled, and loaded to 31 tons per sq. inch. No yield-point was 
passed, and the curves marked E in Diagram 3 show that no yield-point should he 
exjDected until a stress of 31|- tons had been applied. The specimen was then kept 
for four hours at a temperature of from 670° to 690° C., and after cooling it was 
found that a stress of 26 tons per sq. incli caused considerable cree|3ing to occur, and 
that with 27 tons q3er sq. inch a yield-point was certainly passed After recovery 
from the overstrain caused by the application of the load of 27 tons per sq. inch, 
it was found that the yield-point had been raised to Ijetween 35 and 36 tons per 
sq. inch. By comparing these figures Avith those giAmn in the table in the preceding- 
page, it Avill he seen that annealing for four hours at about 680° C. has produced a 
slightly greater efiect than AA'as produced by annealing for a feAv minutes at 730° C. 
* ‘Phil. Trans.,’ A, vol. 193, p. 34, 1899. 
