Effects of Cold Working Under Pressure on Subsequent Yield

A method utilizing high pressure fluid environments is described whereby a three-dimensional subsequent yield surface was determined for 304 stainless steel. Cylindrical parent specimens of this material were prestrained in axial compression under fluid pressure and then small subspecimens were sectioned from these parent specimens. Finite element techniques were used to optimize the parent specimen size so that a zone of uniform axial stress would result during the prestraining. Longitudinal strains in this zone were monitored during the prestraining and the subspecimens were cut from this region in a manner that did not allow the machining to appreciably affect the properties of the specimens. Following this, conventional tension and compression tests were performed on the subspecimens in various fluid pressure environments to determine the yield strengths for the cold-worked material in the direction of the principal axis of prestrain and the two transverse axes. These data are used to construct the three-dimensional subsequent yield surface which clearly illustrates the effects on 304 stainless steel, of cold working under pressure.