THE POWER-FORGING OF CHAIN CABLES. BD 
HEAT TREATMENT THE SOLUTION. 
When the matter was taken up in July, 1914, this was the status.- It was 
found, however, that no very considerable amount of chain had been made by this 
process; so the master shipsmith was instructed to set up his dies and start out as if 
to make chain, with the idea that possibly a little practice might bring the quality of 
the chain up to requirements. This was done. However, the breaks were still below 
requirements, the fracture in every case occurring in the welded quarter of the 
link and showing rather coarse granular structure. 
At a loss to explain the matter, since the welds seemed to be good, and the ham- 
mering on the link appeared to make a better link than a hand-welder could make, 
consideration was given to the possible benefits of heat treatment. It was found 
then that there was no literature on the heat treatment of wrought iron. The iron 
in use had a carbon content of about 0.10 per cent, which is not much below that of 
dead soft steel; but again, no literature on the heat treatment of low carbon steel 
could be found. Nor was the shop equipped for accurate experimental heat treat- 
ment. However, a way was found to heat treat one or two test triplets, and it was 
found that, even though the carbon content was so low, the iron was very respon- 
sive, and that heat treatment made good chain. 
It had been suggested by one or two experts who had been consulted that the 
chain be quenched from a temperature above the critical point, and, if possible, vi- 
brated, this being recommended with a view to stiffening and strengthening it. The 
opposite kind of treatment, however, was that which was found to be successful. The 
reason is that the severe hammering applied to the link by the steam hammer stiffens 
it in the welded quarter, and a partial annealing is required to soften it enough to 
make the quarters deform under the shearing stress which obtains there. This 
permits the total stress to run up until a fracture can be obtained by a combination 
of shear and tension. The practice now is to give the chain an air quench from a 
temperature slightly above the upper critical point. 
The hand-welders had not been successful with the open-link chain. The break- 
ing stress requirement for the stud-link chain was 500,000 pounds. The open-link 
chain required for the Panama Canal could not be brought up to that standard, and 
the inspector had been accustomed to pass chain that broke as high as 450,000 
pounds; but it was shortly found that by the power-forging process, with heat treat- 
ment, the open-link chain could be made to stand stresses as high as 550,000 and 
560,000 pounds. 
The experiments being thus successful, authority was given by the Panama 
Canal Commission, July 30, 1914, and the Navy Department, Bureau of Construc- 
tion and Repair, July 31, 1914, to proceed with the power-forging process of manu- 
facturing chain. 
The equipment in use was, of course, more or less improvised; and during the 
past two years there has been a constant, almost daily, development in the equipment 
and its use. New hammers, especially designed for this service, have been purchased, 
and have proved highly satisfactory in service. The methods of heat treatment have 
