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.
Variation of the absorbed energies and shear fracture appearances associated with the change of the width and the depth under the notch in Charpy impact test were investigated on Al-killed steel in the tem-perature range from -70°C to 20°C. The results obtained are summarized as follows; (1) The clear transition curve of absorbed energy could not be observed when decreasing the width and the depth under notch of specimens. (2) The energy peak in the range from -60°C to -40°C appeared for specimens of the depth under notch, h=2-4 mm, regardless of their width. (3) The shear fracture appearance of the specimens of 10 mm in width showed the tendency of a little in-crease when the depth under notch decreased from 8 mm to 4 mm, but its precise measurement was impossible for specimens of the depth under notch of 2 mm. (4) Describing here the absorbed energy by E=ChmWn, the exponent m was roughly 1.3-1.6 and showed a little but not remarkable dependence temperature for longitudinal specimens. On the other hand, it decreased sharply in the range from -40°C to 20°C for transverse specimens and that range seemed to correspond to the temperature range of υTrs. The exponent n was 0.9-1.1 and showed little dependence on the depth under notch and on the test temperature for both longitudinal and transverse specimens.
In the present paper, the behaviours of restraint force and bending moment and distortion in three-pass welding of medium thick (12.7 mm) HT80 steel plate are investigated experimentally using H-type restrained specimens. The main results are as follows: According as the thermal contraction of weld occurs after welding the first pass, restraint tensile force and bending moment that bends the restraint plates convex upward grow due to nonelastic shrinkage caused in the weld zone and its downward eccentricity about the neutral plane of base plate, though their signs as well as magitudes are changed temporarily when the transformation of austenite accompanying expansion takes place in the weld zone. In each welding of the second and third passes, the initial distortion and restraint force are almost extinguished by the heating, and in the cooling processes the restraint force and bending moment are reproduced in accordance with the magnitude and eccentricity of the shrinkage and expansion. The amount of transverse inherent shrinkage in the weld zone after welding each pass is approximated by subtracting the expansion mostly referable to the phase transformation from the calculated value of plastic contraction induced by constraining the thermal expansion of weld. The experimental values of intensity of tensile restraint for the weld-joints are scarcely affected by their angular distortions.
The purpose of this study is to investigate the mechanism of cold welding and influence of properties of metal, such as hardness, melting point, lattice structure and mutual solubility on weldability of similar and dissimilar metals in air. The following results were obtained. 1. Lattice structure, melting point and work hardning coefficient have influence on weldability of similar metals. At the other hand one of dissimilar metals does not depend on mutual solubility, but mainly on hardness ratio of welded pair. And softer material of welded pair being h.c.p. metal, it is difficult to weld dissimilar metals. 2. With increase of welding deformation, rupture of surface film and metal to metal contact advance and tensile shear load of the joint increases.