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INTERNAL STRAINS IN TREATED TUBE.
INTERNAL STRAINS IN A STEEL TUBE AFTER TREATMENT.
OBJECTS OF THE TEST.
To ascertain if the internal strains in a thin, transverse slice taken from a hollow gun forging represent the strains in the intact forging; that is, whether the state of the metal in a detached slice may be accepted as an index of the state of the metal in the forging, havino• reference to tangential internal strains introduced by the method of heating and quenching a tube at the bore. Also, to obtain data upon the magnitude of the concomitant longitudinal strains, and, furthermore, the effect of exposure to higher temperatures in the elimination of strains introduced by heat treatment.
CONCLUSIONS.
I. The detached slices represent the state of the metal in the intact tube with respect to the direction of the internal strains, and approximately with respect to their magnitude.
II• The metal at the bore is under a higher degree of initial compression than indicated by the detached slices. In the present tests the difference is 3,000 pounds per square inch, the mean compressive stresses in slices which display 25,625 pounds per square inch compressive stress at the bore.
III.	Longitudinal strains of compression at the bore are present, which may be taken approximately at three-fourths of the tangential strains. _ In the present instance the mean results show the longitudinal strains are .78 of the tangential strains.
IV.	The ends of the tube are bell shaped, in consequence of the longitudinal compressive strains at the bore.
V.	The state of the metal at the bore at the ends of the tube, by reason of the bell-shaped form, is under greatly diminished tangential strains.
VI.	Annealing eliminates internal strains. The strains which are introduced into the forging by reason of sudden quenching׳ from a moderately high temperature are removed upon exposure to a moderately high temperature when slowly cooled.
VII.	The elimination of internal strains was practically completed when exposed to a temperature of 1,100° F. About one-half the primitive strains remained after exposure to 700° or 800° F.
VIII.	This relief of internal strains is accomplished without material relative movements of the parts of the forging. That is, the opposing parts which were under different kinds of strains, tensile and compressive, maintain their dimensions and relative positions after annealing unchanged.
REMARKS.
This tube was prepared by the Bethlehem Iron Company by heating and quenching from the bore, following the method adopted in treaL ing- the tubes of the 5-inch R. F. guns.
H. Doc. 508---23