THE ACHIEVEMENT AND MAINTENANCE OF DESIRED DIMENSIONS IN COMPLEX, PRECISION-BUILT STRUCTURES, SUCH AS ROCKET-MOTOR CASES, ARE CRITICAL AND TECHNICALLY INVOLVED PROBLEMS. Their proper functioning demands close dimensional tolerances. Dimensional stability is extremely difficult toACHIEVE IN STEELS AT ULTRAHIGH STRENGTH LEVELS. The problem stems from interacting metallurgical factors which manifest themselves in volumetric and shape changes. The principal sources of size change are the changes in specific volume accompanying the phase transformations which occur in hardening and tempering. Distortion occurs when a part deforms in response to stress. The problem of dimensional instability is analyzed, the factors involved are discussed, and recommendations are made regarding the control of these factors. (Author).

This report deals with the deleterious effects of hydrogen gas on steel at elevated temperatures and/or pressures. Hydrogen attack on steels is manifest as decarburization, intergranular fissuring, or blistering. These conditions result in lowered tensile strength, ductility, and impact strength. The reaction of hydrogen with iron carbide to form methane is probably the most important chemical reaction involved in the attack on steel by hydrogen. Attack of steel at elevated temperatures and pressures is limited or prevented by the following measures: (1) use of steel alloyed with strong carbide-forming elements, (2) use of liners of resistant alloy steels, and (3) substitution of resistant nonferrous alloys.