How to Improve the fatigue performance of the shipbuilding steel ?

Posted: 9/4/2011 11:32:06 PM

Most of the fatigue cracks occurred in the welded joints. If the yield strength of welded joints with a considerable presence of residual tensile stress, the stress of the weld will become easier to focus on the end of the area. Therefore, even if the implementation of the base material of high strength, fatigue strength of welded joints as low, there are many can not achieve the effect of high intensity. Although many have been welded joints on fatigue crack inhibition studies, but until now has not found an effective way. On the contrary, on the welding materials and by improving the weld joints after welding process, which effectively inhibit the occurrence of crack is more.
By TIG (tungsten TIG) welding, the weld face to improve the shape, the method to suppress the occurrence of cracks has been widely used. In addition, the control of the phase transition temperature welding material, welding residual stress imposed by the state to make it possible to improve the fatigue limit.
Treatment after welding of welded joints by mechanical rolling method to improve the weld face shape, thereby reducing the stress concentration method. Such as hammering, etc. is applied weld residual stress methods. It is worth noting that around the 27kHZ ultrasonic mechanical vibrations through the transfer alternating hammer hit the surface of the steel sample method, which is equivalent to rolling through the implementation of mechanical processing, to improve the shape of the weld face to obtain the hammer handling considerable residual stress. Hit of the ways to improve the surface layer of the metal structure, so as to improve the fatigue strength.
Fatigue crack growth, according to the different steel, using different methods to suppress. For example, YP is 36kg/m2 (1kg/m2 = 98.1kPa) level of the plate has been achieved commercially. Another organization using TMCP process to refine the control of research, such as bainitic ferrite in the granular distribution, as well as ferrite and pearlite, fine-grained dispersed. In addition, the ferrite distribution in the martensite was strip is an effective method. Hard martensite to crack as obstacles, regardless of the crack can not wrap, so that cracks in the thickness direction of the expansion rate can be reduced to one-fifth of normal steel.