This study aims to clarify the reason why a low-hydrogen lime type electrode is sensitive to hydrogen porosity of weld metal in spite of its low diffusible hydrogen content. Metal transfer, viscosity of molten slag, and the difference of features of bubble through molten slag are studied by various kinds of electrode fluxes dried or moistened. The experimental results were as follows: 1) From the lower viscosity of molten slag, porous solidified slag and quietly wavy molten pool by low-hydrogen electrode, it was deduced that saturated gas in molten metal might consistently generate to form bubbles and easily escape through covered molten slag before and during solidification period of molten metal. 2) Saturated gas in molten metal with other types of electrodes seemed to escape hardly through molten slag with higher viscosity. And gas under viscous molten slag formed larger blisters on slag surface just after solidification of molten metal and explosively escaped after completion of so.idification of molten metal.
In previous papers, the authors have made it clear that wire melting rates are'not affected by groove widths in electrode positive narrow-gap MAG wleding but that, on the other hand, in the case of electrode negative, the wire melting rate decreases with decreasing the groove width. It was proposed that, some change in the electric input energy with changing groove width was the cause of this phenomenon in the case cf electrode negative MAG welding. This paper attempts to verify the above proposition by measuring both the heat quantity of the molten droplets. and the wire melting rates at different groove widths and calculating the equivalent wire melting voltage. The experimental results were as follows; With the electrode negative, the arc ignited between the conical surface of the wire tip and the groove side walls, and both the heat quantity.of molten droplets and the wire melting rate decreased with decreasing the groove width. Moreover, the calculated equivalent wire melting voltage also decreased with decreasing groove width. On the other hand, with the electrode positive, the heat quantity of molten droplets and the wire melting rate were both not affected by the groove width. It was concluded from the experimental results that, in electrode negative narrow-gap MAG welding, the phenomenon of the decrease of wire melting rate with decreasing groove width, is attributable to a decrease in the equivalent wire melting voltage.
When the arc run-off onto the flat tab plate at the terminal end of joint, longitudinal large crack occurs with high frequency at the point just before the end in one side submerged arc welding. From the result of the observation of the fracture surface, the crack occures at high temperature as just after weld metal solidifies. And crack occurrence isn't influenced upon the kind of welding material and chemical composition of weld metal. Keeping down the welding speed and heating the end of weld joint are effective on crack prevention, and with Sealing Bead process in which the reverse bead is not created at terminal end of weld joint or Crator Conjunction process in which crators are joined at middle of wled joint, end crack don't occur.
Electron microscopic investigation was carried out on dislocation structure of various types of ferrites in as-deposited weld metal of mild steel. Welding processes employed were shielded metal arc welding, CO2 arc wleding, submerged arc welding and clectro-slag welding. Change of weld heat input affected not only the ferrite in size and shape but also its substructure. The microstructures of weld metals consisted of three types of ferrites; proeutectoid ferrites, side plate ferrites and acicular ferrites in all welding processes but electro-slag welding. Acicular ferrite, which occupied the most area contained the rather higher density of dislocation than the other two. Increasing cooling rate tended to cause the decrease of dislocation density in each type of ferrites. Dislocation structure seemed not to be sensitive to welding process, as far as dislocation density was concerned. The dislocation density observed ranged from 109 to 1010cm2 in all welding processes employed. Effect of cooling rate on the internal stress of each ferrite grain was also studied. The internal stress, which was estimated from radius of curvature of dislocations increased with dislocation density in ferrites.
The hardenability of the weld metal compared with roiled steel plate was investigated by means of both the dilatometry and the Jominy test to clarify the transformation behavior of the weld metal. Three kinds of specimens were prepared by the rolled steel plate, Electron Beam (EB) weld metal in the air and EB weld metal in vacuum. The Continuous-Cooling-Transformation (CCT) diagram for the EB weld metal in the air austenitized at 950°C showed that the region of ferrite and bainite formation were shifted to the faster cooling rate. The hardenability of EB weld metal in the air was the lowest and that of rolled steel plate was the highest. It was concluded that the oxide inclusions and the microsegregation across the columnar dendrite lowered the hardenability of the weld metal.
The weld construction using heavy section steel and/or high strength low alloy steel is made by multipass welding. In that case, weld metal is reheated to various temperatures by welding heat of the subsequent pass. This result will lead to both microstructural change and through thickness toughness variation in weld metal. In this work, an investigation was carried out about the reheated zone toughness in weld metal. It is found by this work that, for simple Si-Mn system weld metal, the reheated zone toughness is improved as compared with as-welded touhgness, and increases with the ratio of reheated structure to aswelded structure. This improvement is caused by both the disappearance of columnar structure and the refinement of microstructure. While, for high strength low alloy system weld metal, the reheating shows the complex effect. The reheated zone toughness in this system deteriorates at peak temperature range between 750°C and 950°C, although the remarkable optical microstructural change is not observed. The reheating effect to the toughness of high strength low alloy system weld metal shows the inverse phenomenon as compared with that to the toughness of simple Si-Mn system weld metal.
In order to apply an one-side welding process to the lower temperature service steel plate, the reduction of welding heat input, the reorganization of heat cycles, etc., are requested. From this point of view, Longer Electrode Distance Submerged Arc Process has been proposed, and new type flux which makes possible to weld with such longer electrode distance, was researched. With common flux, the solidified slag formed by a leading electrode has larger electric resistance and thus the arc restriking by a trailing electrode is difficult. In order to get better arc restrikability, it is necessary to make electric conductance of solidified slag more than 0.01 mho/cm at the point of a trailing electrode wire tip. Higher electric conductance and better arc restrikability of the slag can be got with the flux of high TiO2 content, and TiO2-CaF2-Al2O3 system flux is the most suitable to the Longer Electrode Distance Submerged Arc Process.
This paper describes the diffusion bonding characteristics of 21/4Cr-IMo Steel and 13Cr steel. Bonds were made under various conditions of temperature, time and pressure. The specimens were evaluated by metallographic examination and mechanical testing. Results obtained are summarized as follows: 1) The diffusion bond possesses tensile, bend and fatigue properties, which are fully equivalent to those of the base metal. 2) Charpy impact values of the diffusion bond are relatively low compared with those of the base metal. 3) A notched impact test provides the most critical asesssment of the quality of diffusion bonded steel. 4) 21/4Cr-1Mo Steel can be readily diffusion bonded compared with 13Cr Steel.