1978 Volume 64 Issue 1 Pages 60-69
In order to clarify the effect of warm tensile working on the stress relaxation value ΔP/P0 (ΔP: relaxed load, P0: initial load) at room temperature in a carbon steel (ferrite+lamellar pearlite), the effect of predeformation temperature (20°C-320°C), strain and structure have been studled, The results obtained are as follows:
(1) The decrease in the stress relaxation value is observed on specimens which predeformed in the temperature rahge from about 220°C to 270°C. These predeformation tcmperature correspond to the temperature where the strain aging increases with increasing dissolution of the iron nitride and carbide owing to predeformation.
(2) When the lamellar cementite have partially been broken by the predeformation in the temperature range from 20°C to 220°C, the relation between the relaxation value and logarithmic time is a snaky curve and then the relaxation value is shown its maximum value.
(3) While the linear relation is observed for the steel with bended and broken lamellar cementite, in this case the relaxation value increases proportionally with increasing predeformation strain.