Chervyakov M. Stress-strain state and operational strength of welded joints in high-strength nickel alloys.

The thesis is dedicated to investigation of peculiarities of thermal-deformation processes for evaluation of crack resistance of welded joints and, on this basis, development of recommendations for selection of efficient technological approaches to producing sound welded joints in high-strength (?t ~ 1000 MPa) precipitation-hardening nickel alloys containing the strengthening ??-phase. Weldability of nickel alloys was investigated by the Varestraint Test method. The level was determined and kinetics of development of the stress-strain state during formation of a welded joint was studied by the experimental-calculation method in terms of estimation of the probability of hot cracking of the weld zone in fusion welding of precipitation-hardening nickel alloys. Principles of distribution and features of development of local plastic strains in heat-affected zone of nickel alloys were investigated. On the basis of the analysis correlation between the stress-strain state and operational strength , i.e. propensity of welded joints to formation of hot cracks in the course of welding and thermal processing of nickel high-strength alloys is shown. Methods were identified to control the stress-strain state in welding of alloys sensitive to formation of hot cracks in HAZ. The qualitative and quantitative effect of thermal-physical properties of the alloys under consideration, which determine an increased sensitivity of the welded joints to cracking, was investigated. The package of recommendations was worked out to create conditions ensuring the required operational strength of the welded joints.