HARDENED BY OVERSTRAIN. 
17 
Expei'iments ivith Lowmoor Iron. 
The Lowmoor iron, wLich was afterwards emj)loyed in order to show the phenomenon 
of temjjering after hardening by tensile overstrain, was subjected to an examination 
exactly similar to that described above for steel. An iron rod fths of an inch in 
diameter, and somewhat over 6 feet long, was employed, and specimens were tested 
without being previously turned. The analysis of this material wms kindly supplied 
by Messrs. Edgar Allen & Co., Limited, Sheffield, and is as follows :— 
Carbon. 0T2 percent. 
Silicon.0‘149 ,, 
Sulphur.0*011 
Phosphorus.0*076 
Manganese.trace 
Iron (by diiference). . . . 99*644 
100*000 
An ultimate strength of 23 tons per sq. inch was attained with an elongation, 
omitting all local extension, of 24|- per cent, on a 4-inch length, or, allowing for the 
local elongation at the neck which formed just outside the measured length, say an 
ultimate elongation of 27 or 28 per cent, on the 4-inch length. 
Diagram No. 4 shows the elastic properties of this material when tested in the 
conditioii as obtained from the makers. The primary yield-point is shown to have 
occurred at about 17 tons per sq. inch,'^ and the stej:* by which the yield-point is 
raised after recovery from overstrain was about 4 tons per sq. inch. After the 
primary overstrain the yield-point was raised (when elasticity had been restored) by 
about 4|- tons jjer sq. inch, after the second overstrain by 4 tons per sq. inch, after the 
third by less than 3^ tons, while fracture occurred (outside the length under examina¬ 
tion, however) 2^ tons above the fourth yield-point. These figures seem to indicate 
a gradual and consistent diminution, as the load increases, of the step by which the 
yield-point is raised after recovery from overstrain. This is contrary to what was to 
be expected from the experiments with steel; but it may be remarked that Diagram 5, 
which gives the history of annealed specimens of the same Lowmoor iron, shows the 
step by which the yield-point is raised remaining j)ractically constant. 
Curves Nos. 2, 3, 4, 5, and 6 of Diagram 4 show the comparatively rapid rate 
at which Lowmoor iron recovers from tensile overstrain, the recovery only taking 
hours instead of days or weeks as in the case of steel. Curve No. 9 illustrates the 
* Although 17 tons were applied before considerable yielding began, it was found that this yielding 
continued under a stress slightly over 16 tons/sq. inch, so that the yield-point should perhaps be placed 
at this latter stress. 
VOL. CXCVIII.—A. 
D 
