The energy approach to fatigue crack growth of S355 steel welded specimens subjected to bending

•The effect of HT and different R on the durability of the samples was explored.•The effect of the energy approach on FCGR was explored.•Description using the energy model showed better predictive than other approaches.•The hardness in the HAZ and the joint is greater than that of the starting metal. The study presents the results of the research on the rate of fatigue crack growth subjected to bending in the ferritic-pearlitic structure. The studies were carried out at a constant amplitude of the moment and at various values ​​of the load ratios R and at the operating frequency of the machine of 28.4 Hz. Flat specimens made of S355 steel and with fillet welds and with double-sided blunt external notches as well as concave and convex welds were tested. The tests were performed on specimens without and after relief annealing. The study showed that the heat treatment had an influence on the dispersion of the test results described by the energy parameter. It was also observed that the effect of the applied treatment increased the rate of fatigue crack growth.