Published: Jan 1956
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The data show a rather wide range of relaxation strengths. The variation apparently involves several factors: 1. Two or more initial stresses were used at five temperatures for one lot of material ( Material 1 ). Curves of initial stress versus residual stress show a substantial increase in residual stress with increase in initial stress, particularly at lower temperatures and longer times of testing. The material used for these tests was water quenched from 1500 F. 2. The rather low heat-treating temperature of 1500 F for Material 1 apparently caused low strength in relation to the other materials tested. An exception was Material 14 which had abnormally low strength with no evident explanation in the data. Material 9 when quenched from 1922 F had abnormally high strength. However, some specimens heat treated at 1650 to 1750 F had about as high strength when consideration was given to the variations in initial stress. 3. The spread in data probably reflects a variation in response to heat treatment. Vanadium-bearing steels would be expected to vary considerably in their creep resistance due to variation in degree of solution of vanadium carbides when heat treated below about 1750 F. 4. Two specimens restressed after an initial relaxation period, did not show an increase in residual stress. In one case, a higher stress ( Material 4 ) was used for the second test, and in the other a lower stress (Material 3). 5. Initial stresses ranging from about 43,000 psi at 850 F to 25,000 psi at 1050 F were used to establish the location of the comparative curves. Separate curves were used to show the data for the material quenched from 1500 F and for material quenched from between 1650 and 1750 F. The high strengths reported for the material quenched from 1922 F were omitted in placing the curves.