As a result of uneven heating of the metal concentrated source of heat in a welded structure having welding voltage – time and residual. Temporary welding voltage are valid only during the period welding when the temperature of welded metal. Voltage remaining in the metal after welding and complete cooling design, called the residual welding stresses. They arise from constrained thermal expansion and constrained shrinkage of metal during its heating and cooling. This constraint is due to the fact that the locally heated area of welding on all sides surrounded by the cold metal.
Additional fixing the workpiece (in the adaptation, with rigidly fixed) also interferes with normal processes of thermal expansion and shrinkage, and there are reactive residual stresses. When welding alloys with polymorphic transformations in parts of the welded joint metal, heated above the critical point, there are structural stresses. For example, when welding hardenable steels, heat-affected zone which martensite is formed with a large volume effect of transformation, the structural stresses reach high values. Distinguish three types of welding voltage. In welded structures of carbon and low-alloy steels are driven primarily by welding voltage of the first kind.
They are balanced and in amounts commensurate with the size or design of its individual parts. Welding voltage of the second and and third kinds are balanced within the microvolume and the individual grains of the metal. Depending on the direction of action in space distinguish welding voltage linear, or uniaxial, acting only on one axis, planar, or two-axle, acting in two mutually perpendicular directions, volumetric, or three-axle, acting in three mutually perpendicular directions. Direction of the action with respect to the axis cross stitch welding voltage different from the longitudinal. Technology, assembly and welding of structures should be tailored to ensure that the minimum values of welding voltage and when it is dictated by terms of design, include the removal of these stresses. If the values of welding stresses reach the yield point of the metal, then there is its plastic deformation, ie change the size and shape welded construction, called the warp. Arising during welding deformation is divided into time to develop only during the welding of the structure, and residues that remain after the welding and cooling design. Depending on the nature, form and size of the workpiece residual welding deformations are developed "in-plane" and go "out of the plane" of connected elements. Deformation "in the plane" appears in Change (decrease) the size of design, with what must be considered when cutting parts and assembly welding, providing allowance for resizing. Deformation "of the plane (angular deformation) occurs in Education bulge (hlopunov "), the local bending of sheets, the so-called mushroom bending zone during welding of elements of T-and I-sections, as well as other changes in forms of products. The magnitude and nature of residual strains are highly dependent on the thickness and properties of base metal, welding conditions, weld shape, consistency of their performance, design of welded parts. In developing the technology and build weld design should aim to reduce the residual strain. If the value of residual strain goes beyond tolerance, it involves editing the structure.