Effects of flux type of covered electrodes on the fatigue strength of one-pass fillet welded joints

It is generally recognised that the flux type of covered electrodes affects the profile and mechanical properties of welds and may well control the fatigue strength of fillet welded joints. Fillet welded joints, however, have seen few systematic investigations. The purpose of this investigation is to improve the fatigue strength of fillet welded joints through appropriate design of the covered electrode flux.Ten types of covered electrode were trial-manufactured with variation in the flux system at two levels (to improve the profile of the fillet toe region) and the added alloying element contents of each system at five levels (to vary the hardness of the weld metal). These covered electrodes were used to prepare non-load-carrying cruciform fillet welded joints using 570 MPa class high-strength steel base metal. Fatigue tests (S = σmax - σmin, σmax = σY) were run with the fillet welded joints. The results obtained may be summarised as follows: The profile of the fillet welds appears to be affected by the flux system and base metal but not by the added alloying elements. The maximum stress concentration factor (Kmax) is reduced to Kmax ⌣ 1.59 for covered electrodes using an MgCO3-MgO-CaF2-iron powder system flux (M' series). The fatigue strength of the fillet welded joints at 2 × 106 cycles is improved to around 143 MPa in the M' series. It can safely be said that there is an inverse correlation between Kmax in the toe region and the fatigue strength of the welded joints. Appropriate relations are developed and used to calculate the recovery to the weld metal of added alloying elements. The recovery to the weld metal of the added alloying elements on average gives minima of around 98%Ni, 94%Mo, 85%Cr (which are good), and around 11%B.