The article discusses the effect of the thermal conditions applied during the MAG welding of steel S960QL and the mutual annealing of runs on the mechanical properties as well as on the macro and microstructure of welded joints made using various values of cooling time t_8/5. The research described in the article also involved the comparison of the above-named results with those obtained during a thermal simulation. In addition, the article presents the test results concerning the examination of the coarse and fine-grained areas of the HAZ of welded joints. The test results made it possible to optimise the value of cooling time t_8/5 when welding steel S960QL.