Abstract
The effect of post-weld heat treatment on mechanical properties, microstructure and fracture mode of low-alloyed CrMoNb steel was examined using an optical microscope, and a scanning and transmission electron microscopes. Steel plates, 18 mm thick, were welded by means of the submerged arc welding technique and then heat treated in the temperature range from 475 to 700 °C. It was found that the tensile strength, hardness and impact energy values decrease with the increasing annealing temperature, except for annealing at 550°C and 625°C. Anomalies were attributed to the precipitation of fine carbides. Complex cementite proved to be beneficial in controlling the fracture mechanism in impact (Charpy V-notch) and tensile tested specimens.

Key words
low-alloyed steel, welding, mechanical properties, microstructure, fracture surface

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