Longitudinal tensile test on weld metal in fusion zone at high temperature

Abstract

To determine the mechanical properties of welds used in fire resistant steel structures at different temperatures, the mechanical properties of welds subjected to elevated temperatures are investigated in this study. This is achieved by carrying out steady-state tensile tests on welds composed of Q235 base metal with an E4303 electrode and Q345B base metal with an E5015 electrode. This paper presents the results of analyses on the failure mechanisms and metallurgical structures of welds at high temperatures. Based on the stress-strain curves of welds at a specific temperature, the mechanical parameters and reduction factors are listed (including the elastic modulus, yield strength, and ultimate strength), and comparisons with current design standards are presented. This paper reveals that the elastic modulus and yield strength of the welds gradually decreases with increasing temperature. By contrast, the ultimate strength of welds first increases and then decreases with increasing temperature, reaching a maximum value at 300 °C. The comparison shows that CECS 200:2006, AS 4100, Eurocode 3, and AISC 2010 are very conservative in predicting the degradation of the elastic modulus. The recommendations of current codes are not fully applicable to the reduction of yield strength and ultimate strength of E4303 and E5015 welds, especially at 500 °C and higher, and it is unsafe to use the recommendations of current codes to predict the mechanical properties of welds.