1978 Volume 47 Issue 1 Pages 18-25
The development of a new welding flux which has been applied successfully to large heat input one-side sumberged arc welding (>250 KJ/cm heat input) to 50 Kg/mm2 class steel is described.
It has been demonstrated that the Si-Mn weld metal using commercially availabel flux for midi steel is occasionally not sufficient to large heat input welding of 50 Kg/mm2 class steel with respect to the notch toughness and ductility, especially when used with matching strength and higher level of hydrogen content.
A means of overcoming those problems by the use of Si-Mn-Ti-B weld metal has been described. This method provides uniform structure of ferrite and pearite, because free B suppresses the nucleation of large primary ferrite along r grain boundaries and Ti acts to suppress the formation of boron nitride. It was found that suitable composition ranges of Ti and B are 0.01 to 0.02% Ti and 0.003 to 0.005% B at about 1.3% Mn.
To provide this optimum range of Ti and B to the one-side submerged arc weld metal, a completely new baking type flux has been developed. The flux is CaO-MgO-TiO2-SiO2 type containing TiO2 as one of the main constitutents and a small quantity of B2O3. Ti and B are introduced to the weld metal by the reduction of those two oxides during the wleding, respectively. Suitable range of flux constituents are discussed mineralogically so as to provide stable mechanical properties and welding workability for entire plate thickness ranging from 12 to 40 mm.
The characteristics of welding result with the newly developed TiO2 type flux are as follows: (i) The flux shows good workability, namely, good bead shape and good slag detouchment. (ii) Weld metal shows higher notch toughness and yield strength at moderate tensile strength. (iii) And tensile strength of weld metal is less depend on the carbon equivalent.