Fatigue performance of Q420C steel fillet-welded joints at low temperatures

Abstract

This paper focuses on the fatigue performance of Q420C steel fillet-welded joints at low temperatures. The tensile tests and Charpy V-notch tests were first performed to evaluate the mechanical properties of Q420C steel fillet-welded joints under room and low temperatures. It reveals that the yield and ultimate strengths increased with reducing temperature from 20 °C to −50 °C. The Charpy impact energy transition temperature (ETT50) was –33.67 °C. Subsequently, the fatigue test was conducted on the fillet-welded cruciform joint specimens of Q420C steel at 20 °C, 0 °C, −15 °C, −30 °C, 40 °C and −50 °C considering three stress ranges (i.e., 0.0–0.5 ftw, 0.0–0.7 ftw and 0.0–0.9 ftw), where ftw was the design strength of fillet weld. The micro-morphologies of fatigue fracture surfaces were observed by scanning electron microscope (SEM), and the river patterns indicating brittle fracture occurred at −50 °C. The S-N curves and P-S-N curves with a survival probability of 95% were fitted from experimental fatigue life. With decreasing temperature from room temperature (20 °C) to −40 °C, the fatigue life increased at low-stress range (0.0–0.5 ftw), while shrank at high-stress range (0.0–0.9 ftw). Then, the fatigue life presented a declination trend at −50 °C for these three stress ranges, compared with that at −40 °C.