FORMATION OF COLD CRACKS IN WELDED JOINTS FROM HIGH-STRENGTH STEELS WITH 350-850 MPa YIELD STRENGTH

摘要

The main problems in welding of high-strength steels are connected with their susceptibility to cold crack formation. As a rule such cracks are nucleated in HAZ of welded joints under the effect of tensile stresses. Diffusible hydrogen and presence of hardening structures in metal accelerate this process. Given paper presents a comparative analysis of effect of structure, diffusible hydrogen and residual stresses on cold crack resistance of welded joints from high-strength structural steels differ in chemical composition and level of static strength. Experiment-calculation methods of investigation were used for study of microstructural changes and formation of stress-strain state in rigidly fixed welded joints. Resistance of welded joints to cold crack formation was evaluated based on results of testing of technological samples and specimens on Implant method. It was determined as a result of performed investigations that probability of formation of longitudinal cold cracks in rigidly fixed welded joints from high-strength steel changes in wide ranges. However, there are specific regularities related with effect of the residual welding stresses on this processes. Increase of diffusible hydrogen content in deposited metal, steel carbon equivalent, cooling rate and stress-strain state of welded joints reduce their cold crack resistance. Results of performed investigations can be used in development of technological processes of welding of high-strength steels with yield strength from 350 to 850 MPa and carbon equivalent from 0.35 to 0.70%.