Special features of formation of defects in explosion welding of two-layer large plates

Continuity check results of two-layer plates from several consignments are given. A shock pinched plasma generator and explosion welding technique on its base are developed, application of which allowed for excluding discontinuity formation at the beginning of welding and for eliminating stabilization area of joint efficiency and wave structure.     

Special features of forming thick‐walled welded joints in brazing and fusion welding

The results of comparison of brazed scarf joints of different design on the basis of the distribution of working stresses are presented. The design of the tooth-type brazed joint is proposed and the joints are evaluated by the finite element calculations which show only a slight stress concentration in the joints of this type.     

Special features of the formation of welded joints in vertical laser-arc welding of low-alloy steels

ABSTRACT

Investigations were carried out into the special features of the technology of vertical laser-arc welding of large structures made of high-strength and low-alloy steels with a variable welding gap and a large root face.

The parameters of the conditions of vertical laser-arc welding of root passes in the low-alloy steel 30–40 mm thick with a root face of 10 mm (welding speed, the amplitude and frequency of transverse oscillations, the intensity of welding current, arc voltage, laser radiation power) resulting in the formation of high-quality welded joints are determined. The experimental results show that the laser radiation power, required for producing continuous penetration of the root face, depends on the thickness of the parent metal: for the metal thickness of 14–30 mm the sufficient laser radiation power is 3.8 kW, for a thickness of 40 mm it is no less than 4.6 kW to penetrate a depth of 5 mm.

The welded joints have a fine-dispersed acicular structure of the martensitic – bainitic type. The experimental results were used to develop a technology of welding of low-alloy steels of different thickness using robotic equipment.     

On the mechanism of porosity formation during welding of titanium alloys

The mechanism of porosity formation during the fusion welding of titanium and its alloys is studied. Porosity formed during the electron beam welding of titanium is characterized using high-resolution X-ray tomography, residual gas analysis and metallographic sectioning; the results confirm that porosity formation is associated with evolution of gas, especially hydrogen. A model for hydrogen diffusion-controlled bubble growth is proposed, to aid in the interpretation of these findings. To investigate further the effect of hydrogen on porosity formation, hydrogen charging is used to achieve different hydrogen levels prior to welding. The results confirm that porosity can be suppressed even at every high hydrogen levels, when welding is carried out with optimized welding parameters and perfect joint alignment; on the other hand, porosity is exacerbated when a small beam offset is employed. This is because any beam offset alters the size of the liquid zone at the melting front, where the joint edges first become melted. It is proposed that the thickness of the liquid film at the melting front is crucial for bubble nucleation and bubble survival in the weld pool; bubbles can escape through the keyhole by breaking through this liquid film, when it is too thin. This challenges the common assumption of bubble escape by flotation to the weld pool surface. Thus the nucleation rate in the liquid zone at the melting front determines the likelihood of porosity occurring. This suggests that the beam offset is likely to be one factor influencing porosity formation in these circumstances. The paper provides fundamental insights into the mechanism of porosity formation during the welding of titanium alloys and guidance to aid in its elimination.     

Special features of pulsed arc welding of titanium

The special features of pulsed arc welding of titanium are described.     

Special features of welding highly stressed titanium alloy structures

Investigations were carried out into the quality of welded joints in submerged-arc welding and also the problems of consumption of electrode material at higher currents. Methods for improving the quality of permanent joints when using tungsten electrodes are outlined.