Exhaustive series of mechanical tests leads to better understanding of the effects of previous cold work, welding and heat treatment on the tensile properties, notch toughness and the resistance to repeated loadings of two pedigreed heats of steel.Tests conducted under the auspices of the Fabrication Division, Pressure Vessel Research Committee.In 1946 the Fabrication Division of the Pressure Vessel Research Committee instituted a research program at Lehigh University, the purpose of which was to study the effects of fabrication processes such as cold-forming and welding on the mechanical properties of steels used in the manufacture of pressure vessels.It was hoped that this program would produce information as to whether present steel specifications are adequate to provide material of the proper characteristics for use in pressure vessels.