EFFECT OF DIFFUSIVE HYDROGEN AND RESIDUAL STRESSES ON COLD CRACKING IN WELDING OF LOW-ALLOY HIGH-STRENGTH STEELS

摘要

Considered is the mathematical model of risk of cold crack formation in rigidly-restrained welded joints of structural high-strength steels, which is based on calculation-experimental data concerning microstructure, content of diffusive hydrogen and stressed state in elementary volumes in the welded joint zone. The initial data for the mathematical modelling were the results of measuring the thermal cycles of welding, the data, found experimentally, about the content of diffusive hydrogen in deposited metal and relationships, which characterize the change in metal yield strength in the heat-affected zone of welded joints depending on temperature and its microstructural state. The probability of initiation of cold cracks in welded joints depending on content of diffusive hydrogen in deposited metal, preheating of welded joints, their stressed state and structural state of metal at the area of overheating of heat-affected zone were evaluated from the results of testing the technological samples (not less than 10 for each technological variant of welding). It is shown on the example of welded joints of steel 14KhG2SAFD that the probability of formation of longitudinal cold cracks in them is changed within wide ranges depending on initial temperature of metal and hydrogen content, however there is a definite regularity connected with effect of residual welding stresses on this process. Quantitative characteristics of required conditions of formation of cold cracks in welding of low-alloy high-strength steels are manifested quite clearly in use of a probability model of Weibull's brittle fracture.