[en] Properties in the heat affected zone of joints welded by the submerged arc process with a high heat input have been studied. Steels were C-Mn, C-Mn-Nb and C-Mn-V. Two parameters have been proposed to characterize the thermal field: the cooling time between 800 and 500⁰C (tr 8/5) and the retention time above 1050⁰C at the fusion line. The first one is easy to measure and may be used to control the welding operation. The second one allows to characterize more completely the thermal cycle at the fusion line and may be determined by means of tables or charts in function of the heat input and of the geometry of the joint. Local properties in the HAZ have been evaluated by transverse tensile tests, hardness tests and Charpy V impact tests with the notch located of different distances from the fusion line. Wide plate tensile tests having a machined notch situated at the fusion line have been performed. Concerning impact properties in the HAZ, similar trends were observed for all the steels, showing a deterioration which had generally its peak value at the fusion line. Nevertheless, it did not result in a change in the class of weldability of the steel. Wide plate tests confirmed the good behavior of C-Mn and C-Mn-Nb steels showing a very satisfactory value of the overall residual ductility. Regarding practical applications, it may be stated that C-Mn-Nb steels did not preset any problem of ductility in the HAZ, even when they were welded with high heat input. These results showed also that wide plate tests must be preferred for characterizing welded joints because local measurements such as impact tests are less discriminative