Effect of the Difference in Temperatures of Phase Transformations on Delayed Fracture of Welded Joints

The resistance of the zone of thermal effect to delayed fracture is primarily determined by three factors, namely, the presence of mobile hydrogen and the structure and rigidity of the stress state. Experiments show that the resistance to delayed fracture depends much on the difference in the temperatures and times of phase transformations in the zone of thermal effect and in the metal of the weld, as well as by the diffusivity of hydrogen in the weld metal. Other conditions being equal, the decrease in the difference of the temperatures of phase transformation in the matrix metal and in the weld raises the resistance of welded joints to the formation of cold cracks. Steels with a strength of up to 650 MPa can be welded by nickel-free electrodes; stronger steels should be welded with the use of welding materials in which the faced metal has the lowest initial temperature of martensitic transformation. These data have been confirmed in repair of parts of a Marion-204M excavator.