Estimated effect of heat input on formation of cold cracks in heat-affected zone of weld

The possibilities of modern computer technologies to efficiently calculate the parameters of the welding process that influence the formation of cold cracks in the heat affected zone were studied. Cold cracks are typical defects of the welds in medium and high-alloy steels. MathCAD software can be used to solve technological problems on the basis of the classical model of thermal welding processes. It is found that the highest values of the instantaneous cooling rate in the heat-affected zone are on the melting boundary. When heat input decreases, instantaneous cooling rates increase. Therefore, the formation of cold cracks between the weld and HAZ is largely due to the formation of hardening structures. If the heat input increases tenfold, the width of the melting zone increases about three times, but the instantaneous cooling rate reduces in order to prevent the formation of cold cracks by selecting modes with the increased heat input. The tenfold increase of the heat input of the welding mode leads to a tenfold increase in time and to the three times increase of the width of the overheating zone. This reduces the strength characteristics of the metal and, therefore, limits the possibility of regulating heat input to reduce the magnitude of the instantaneous cooling rate. On the HAZ periphery, where the maximum temperature does not exceed 150 °C, low instantaneous cooling rates can not be the cause of hardening structures appearance. So, the main reasons for the formation of cold cracks in this area are residual welding stresses or diffusible hydrogen. With different values of heat energy a sustainable ratio of radius-vectors with the corresponding isotherms is observed. This can be used in practice to estimate the size of the HAZ depending on the width of the weld. The use of the MathCAD software allows to quickly optimize the welding mode in order to prevent the formation of cold cracks and avoid overheating of the metal in the heat affected zone.