Temperature Effects on the Mechanical Behaviour of Low‐Carbon Alloyed Pipeline Steel

Abstract

This paper investigates the influence of elevated temperature on the mechanical behaviour of low‐carbon alloyed X70M pipeline steel through steady‐state tensile testing. Cylindrical tensile specimens with a diameter of 6 mm were machined along the rolling direction and tested in accordance with EN ISO 6892‐1/2. Tensile experiments were performed at five temperatures, namely room temperature, 100 °C, 300 °C, 500 °C, and 700 °C, under a constant strain rate of 0.00025 s–1 while maintaining identical specimen geometry and a gauge length of 30 mm. The objective of the study was to evaluate the temperature‐dependent mechanical resistance and deformation characteristics of the steel under elevated‐temperature conditions. The experimental results revealed a progressive decline in the modulus of elasticity and yield strength as temperature increased, as indicated by the calculated reduction factors. The degradation in mechanical strength became more pronounced at higher temperatures, indicating thermal softening of the material. Conversely, the steel exhibited enhanced ductility as temperature increased, as evidenced by significant necking before fracture and greater plastic deformation capacity. In addition, the evolution of smooth and continuous stress–strain curves at elevated temperatures suggests increased dislocation mobility and the activation of thermally assisted recovery mechanisms. These processes reduce strain localization and lower the strain‐hardening capability of the material, contributing to overall mechanical softening. The findings provide valuable insight into the thermo‐mechanical performance of X70M pipeline steel and support the assessment of its structural reliability and safety in high‐temperature service environments.