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What is welding stress? Learn these three methods to remove easily!
Release time:
2021-08-25
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1. What is welding stress Welding stress is the stress of welded components due to welding. The internal stress generated in the weldment during the welding process and the change in the shape and size of the weldment caused by the welding thermal process. The uneven temperature field of the welding process and the local plastic deformation and the organization with different specific volume caused by it are the root causes of welding stress and deformation. When the uneven temperature field caused by welding has not disappeared, this stress and deformation in the weldment is called transient welding stress and deformation; the stress and deformation after the welding temperature field disappears is called residual welding stress and deformation. In the absence of external forces, the welding stress in the weldment
The welding stress is the stress of the welding member due to welding. The internal stress generated in the weldment during the welding process and the change in the shape and size of the weldment caused by the welding thermal process.The uneven temperature field of the welding process and the local plastic deformation and the organization with different specific volume caused by it are the root causes of welding stress and deformation.When the uneven temperature field caused by welding has not disappeared, this stress and deformation in the weldment is called transient welding stress and deformation; the stress and deformation after the welding temperature field disappears is called residual welding stress and deformation. In the absence of external forces, the welding stress is balanced within the weldment. Welding stress and deformation can affect the function and appearance of weldments under certain conditions.
Welding residual stress has six effects on the weldment:
1. Impact on strength:If there are serious defects in the high residual tensile stress region, and the weldment works below the brittle transition temperature, the welding residual stress will reduce the static load strength. Under the action of cyclic stress, if there is residual tensile stress at the stress concentration, the welding residual tensile stress will reduce the fatigue strength of the weldment. The fatigue strength of weldment is not only related to the magnitude of residual stress, but also related to the stress concentration coefficient of weldment, the stress cycle characteristic coefficient [6][min]/[6][max] and the maximum value of cyclic stress [6][max]. The influence of which is weakened with the decrease of stress concentration coefficient and intensified with the decrease of [6][min]/[6][max], decrease with increasing [6][max]. When [6][max] is close to the yield strength, the effect of residual stress gradually disappears.
2. Influence on stiffness:The superposition of the welding residual stress and the stress caused by the external load may cause the local early yield of the weldment to produce plastic deformation. The stiffness of the weldment will therefore be reduced.
3. Influence on stability of pressurized weldment:When the welding rod is compressed, the welding residual stress and the stress caused by the external load are superimposed, which may cause the rod to yield locally or cause the rod to lose stability locally, and the overall stability of the rod will be reduced. The effect of residual stress on stability depends on the geometry and internal stress distribution of the member. The influence of residual stress on non-closed section (such as I-shaped section) is greater than that of closed section (such as box section).
4. Impact on machining accuracy:The existence of welding residual stress has varying degrees of influence on the machining accuracy of weldments. The smaller the stiffness of the weldment, the greater the amount of processing, the greater the impact on accuracy.
5. Influence on dimensional stability:The welding residual stress changes with time, and the size of the weldment also changes. The dimensional stability of the weldment is affected by the residual stress stability.
6. Influence on corrosion resistance:Welding residual stress and load stress can also lead to stress corrosion cracking.
Effect of welding residual stress on structures and components:
Welding residual stress is the initial stress on the cross section of the component that has not yet borne the load. In the service process of the component, it is superimposed with other working stresses caused by the load, causing secondary deformation and redistribution of residual stress, which will not only reduce the stiffness and stability of the structure but also under the joint action of temperature and medium, it also seriously affects the fatigue strength of the structure, the ability to resist brittle fracture, and the ability to resist stress corrosion cracking and high temperature creep cracking.
At present, the failure methods used to eliminate stress include vibration aging (eliminating 30% ~ 50% of stress), thermal aging (eliminating 40% ~ 70% of stress) and hokenergy PT aging (eliminating 80% ~ 100 of stress).
vibration aging
Vibration aging treatment is a commonly used method to eliminate the internal residual internal stress of engineering materials. When the vector sum of the residual internal stress and additional vibration stress of the workpiece reaches more than the yield strength of the material, the material undergoes trace plastic deformation, so that the internal stress of the material can be relaxed and reduced.
thermal aging
Heat aging is to heat the workpiece to the elastic-plastic transition temperature and keep it for a certain period of time to relax the residual stress of the workpiece, and then reduce the temperature very slowly to make the workpiece in a low stress state after cooling. The production time shows that if the process parameters are improperly selected in the process of heating, heat preservation and cooling, or the reasonable process specifications are not strictly observed during operation, the results of stress elimination are often not obtained, and even the stress of the workpiece is increased.
Hawk energy aging
1. At present, it is the most complete aging method to eliminate welding residual stress and produce ideal compressive stress. Hawke can eliminate 80% ~ 100.
The fatigue strength of welded joints can be increased by 50%-120, and the fatigue life can be extended by 5-100 times. The corrosion resistance of metals in corrosive environments is improved by about 400.
3, used to eliminate welding stress can completely replace heat treatment, vibration aging and other aging methods, and the treatment process is simple, the effect is stable and reliable (want to deal with where to deal with, and can be at any time, any process, let you do whatever you want, handy, simple and convenient to use).
4. It is not limited by the material, shape, structure, thickness, weight and site of the workpiece, especially in the construction site, welding process and welding repair, it is more flexible and convenient to eliminate welding stress.
5. The welding surplus height, pit and undercut at the welding toe can be directly processed into a smooth geometric transition, thus greatly reducing the stress concentration coefficient.
6. The micro cracks and slag defects at the weld toe can be removed to inhibit the early initiation of cracks.
7, because the Hawk can eliminate stress treatment can improve several factors affecting the fatigue performance of the weld at the same time, such as residual stress, micro cracks and defects, weld toe geometry, surface strengthening, etc., so it is the most effective method to improve the fatigue performance of the weld at present, and has a multiplier effect.
8. It is more suitable for the stress relief treatment of site welds, ultra-high and ultra-low welds and welding repair welds of large structural parts.
9, environmental protection, energy saving, safety, no pollution, the construction site use more flexible and convenient.
Reprinted from welding and cutting online, infringement must be deleted
Key words:
Method, stress, welding, residual, influence, aging, elimination, reduction, deformation, stability
