Asymmetric cyclic deformation behavior of SA 333 steel at elevated temperatures

Abstract

Purpose The purpose of this paper is to study the effect of mean stress and stress amplitude on the asymmetric cyclic deformation behavior of SA333 Gr-6 C-Mn steel. Such type of loading may arise during the service period because of the load fluctuations, thermal gradients and sudden loading like seismic events. Tests were also carried out at different temperatures to understand the effect of it on sensitiveness of the materials deformation behavior. Design/methodology/approach Cylindrical specimen of 8-mm gauge diameter and 15-mm gauge length was fabricated from the pipe section along its axis. Stress controlled ratcheting tests were carried out by using triangular waveform for cyclic loading. The strain accumulations were measured using 12.5-mm gauge length extensometer. Ratcheting tests were carried out at fixed stress amplitude of 400 MPa and mean stress varying from 0 to 75 MPa, whereas at the fixed mean stress of 100 MPa and stress amplitude varies from 300 to 400 MPa at 300°C. To study the effect of temperature on ratcheting behavior, tests were carried out at a load of 100 MPa mean stress and 350 MPa stress amplitude, with a varying temperature between room temperature and 350°C. The stress rate of 115 MPas-1 was kept constant for all the tests. Findings Increase in mean stress and stress amplitude, ratcheting strain and plastic strain amplitude increases, whereas ratcheting life decreases. With an increase in temperature, ratcheting life increases and strain accumulation decreases up to 300°C, whereas on further increase in temperature, strain accumulation increases with reduction in ratcheting life. Minimum ratcheting rate was observed at 250°C and 300°C. The dynamic strain aging (DSA) phenomena lead to the hardening of the material. The investigated steel shows DSA temperature regime lies between 250°C and 300°C. The failure modes at 250°C and 300°C temperature was transgranular, whereas at 350°C complete ductile. Research limitations/implications The stress rate and loading condition may vary to study the ratcheting behavior. Practical implications From this study, the critical cyclic load may be determined. The DSA temperature regime of this material is determined at this stress rate. This could help to evaluate the cyclic deformation behavior of the material with temperature changes. Originality/value In this investigation, the DSA temperature regime has been determined where maximum ratcheting life, minimum strain accumulation and ratcheting rate were observed. The critical load where the minimum life of the material occurred at elevated temperature is 100 MPa mean stress and 400 MPa stress amplitude.