• • ' NOTES ON CHAIN CABLES. 171 



erties according to the character of the heat treatment given. Such heat treat- 

 ment may be considered under three heads : 



( 1 ) Single heat treatment — slow cooling — annealing. 



(2) Single heat treatment — rapid cooling — hardening. 



(3) Double heat treatment — rapid cooling and drawing — hardening and 

 toughening. 



Tests. — In order to determine the value of these various heat treatments and 

 further the necessity of heat treating chain immediately upon completion and be- 

 fore issue, a set of preliminary experiments was conducted at the Boston Navy 

 Yard, which experiments it is hoped to continue and to extend. 



The results of these experiments are shown in Fig. ^2, Plate 106. These tests 

 were carried on with very crude equipment and cannot be considered as absolutely 

 correct. They give, however, a very clear indication of the effect produced by heat 

 treatment and the eft'ect of dift'erent rates of cooling, and point the wisdom of fur- 

 ther experiments along this line. Series "B" covers the same tests as series "A," 

 except that the bolts were tumbled in a rattler in the foundry for about four hours 

 in order to show the effect of vibration. There is a slight increase in ten- 

 sile strength and elastic limit resulting, but not sufficiently marked to draw any 

 conclusions. However, a slight increase is to be expected, due to the hardening 

 effect of cold working. The tensile strength obtained by cooling in water in series 

 "B" is considered abnormal and not to be relied upon ; it should be noted, however, 

 that in series "A" the tensile strength has been raised from 47,500 pounds per 

 square inch with slow cooling in furnace, to 59,000 pounds per square inch with 

 rapid cooling in water. The elastic limit rises with the tensile strength and the con- 

 traction of area and elongation decreases with the rise in tensile strength. This 

 wide range of quality indicates the desirability and necessity of suitable heat 

 treatment. 



It is probable that between these wide limits there is a mean condition that will 

 give a reasonable tensile strength with satisfactory ductility. It is possible that the 

 treatment, which is most satisfactory from a material point of view, would be too 

 expensive to permit of its adoption. The effect of double heat treatment should 

 be noted in the curves. The material was first heated to 1,675° ^■> quenched in 

 water and then reheated to temperatures varying from 350° to 750° F. by 100° 

 steps. As was to be expected, this resulted in a decrease in tensile strength and 

 elastic limit and a rise in contraction of area and elongation as the temperature in 

 the second heat was increased. By such a process it should be possible to produce a 

 very satisfactory material, but the expense of such treatment of large chain would 

 be prohibitive. It is worthy of note that such wide variation in tensile strength and 

 ductility can be obtained with a material of such low carbon content — .03 to .10 

 carbon. 



A large furnace for the heat treatment of chain is now being installed at the 

 Boston Navy Yard, and it is expected in the future to heat treat all chain before 

 issuing to the service. This furnace is an overhead checkered crown oil-burning 



