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Influence of microfissures in submerged arc welds in high alloyed stainless steel - part II

Joakim Wahlsten, Joakim Hedegård, Mats Randelius, Mats Larsson, Peter Nerman

Abstract

When welding fully austenitic materials it is well known that hot cracking can occur in the weld deposit to a varying extent. The cracks can be of both macroscopic and microscopic size. The influence of internal microfissures on the structural integrity of the joint and especially the fatigue strength has been discussed during the last decades.

In a previous project at Swerea KIMAB this influence has been studied in submerged arc welds (SAW) in two highly alloyed stainless steels. In that study the fatigue specimens produced were fine milled i.e. the weld geometry was removed. This was done to isolate the influence of the microfissures. The testing comprised two series per material, one having a large amount of microfissures and one with a low amount. It was concluded that the microfissures have an impact on the fatigue resistance of the welds but that high fatigue strengths were recorded.

In this continued study one of the previously tested materials is evaluated again but this time with as welded geometry. The fatigue cracks were all initiated at the weld toe and propagated through the base material. The parameters used to create the difference in occurrence of microfissures also results in a difference in weld cap geometry. The fatigue result still shows a difference between the welds with a high and low amount of microfissures. However, this time, it is not due to the amount or position of microfissures but caused by differences in the weld geometry. The weld toe angle for instance, differs by an average of 10 degrees between the two welds.

Computer simulations of the specimens together with the fatigue test results were used to evaluate FAT-classes for the joints. The simulations aimed to assess the structural hot-spot stress at the weld toe. The fatigue resistance against structural hot-spot stress resulted in FAT118 — FAT119 which is better than that of the design criteria of FAT100.

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Senast ändrad av: Peter Hjertsson
26 mars 2015

 


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