1995 年 13 巻 4 号 p. 597-605
It is commonly known that the flux type of covered electrode affects the profile of welds as well as their mechanical properties, and eventually the fatigue strength of welded joint might be controlled. But, there are few investigations performed systematically on fillet welded joint. The purpose of the investigation is to improve fatigue strength of fillet welded joint by appropriately designing the flux of covered electrode.
Ten kinds of covered electrodes are produced trially by appropriately adjusting the flux system of covered electrode to 2 levels to improve the profile of fillet toe region and the quantities of added alloy elements contained in each system to 5 levels to vary the hardness of weld metal. By using them, non-load-carrying cruciform fillet welded joints were made, where their base metal was 570 MPa class high tensile strength steel. Fatigue tests (S=σmax-σmin, σmax=σY) were performed by using the fillet welded joints. Main results obtained are summarized as follows:
(1) The profile of fillet weld was apparently affected by flux system and base metal and was never affected by added alloy element.
(2) Maximum stress concentration factor (Ktmax) at toe was rendered small being Ktmax≅1.59 for covered electrode with MgCO3-MgO-CaF2-Iron powder system flux (M' series).
(3) The fatigue strength at 2×106 cycles of fillet welded joint could be improved to about 143 MPa for M' series. It can safely be said that there is an inverse correlation between Ktmax at toe and fatigue strength of fillet welded joint.
(4) Recovery of alloy element into weld metal could be revealed to calculating formulae. Recovery of added alloy element was excellent being about 98-85% for Ni, Mo and Cr, and the lowest about 11% for B.