Stress relaxation and its effect on tensile deformation of steels

The tensile deformation of metallic materials, when interrupted without unloading, exhibit relaxation of stress. The stress relaxation phenomenon can alter the mechanical behavior of the materials. Stress relaxation phenomenon during tensile test is studied in three steel grades with different microstructures. The influence of stress relaxation on uniform elongation has not been reported before. The uniform elongation varies with strain at which material relaxes and is found to increase upto 3.5%. Contradicting with the published results, the stress drop during stress relaxation varies with strain and the possible reasons are explained. The stress drop during relaxation is governed by strain hardening mechanism in low carbon steel and strain aging mechanism due to martensite in dual phase (DP) and transformation induced plasticity (TRIP) steels.