STRESS RELIEF OF GRAY CAST IRON

The report describes a number of experiments on the stress relief of gray cast iron. One set of experiments consisted of making relaxation tests and using the rate of relaxation as a means of evaluating stress relief. These studies showed that 1 the rate of stress relief is most rapid during the first hour at temperature 2 the rate of stress relief is very slow below 1000 F, but increases as the temperature is raised and 3 initial stress and alloy composition have an important influence on the rate of stress reduction by heat treatment. Observations of heat treatments on highly stressed cast wheels revealed that 1 indoor aging and low-temperature 600 F heat treatment are ineffective for stress relieving, 2 furnace cooling after heat treatment produces lower residual casting stresses than air cooling, and 3 relaxation tests agree closely with results of stress-relief heat treatments of experimental castings.