In order to investigate the behavior of porosity caused by hydrogen in horizontal fillet welding, the growth and the distribution of porosity were studied using flux coated electrodes with varions water contents. 1. Growth of porosity The growth of porosity becomes most remarkable when the hydrogen content of the weld is in a certain value, i.e. 15-17 cc/ 1OOg as diffusible hydrogen content. At higher hydrogen content, the pores become Smaller and porosity formation changes to bubbling type from non bubbling type. In bubbling type, the special solidification lines appear in the solidification structure of the pheriphery of pore. These lines may be caused by the rise of bubble from the pore to the molten pool. In consequence of this behavior, the growth of prosity becomes difficult and smaller pore are formed. 2. Distribution of porosity According to the measurements of length and diameter of pore, pores in a weld may be clasified into following 2 categories: A. Pores with length shorter than l1 (-1.2 mm) B. Pores with length longer than l2 (l2<l1) And the proes with length l1-l2 are very few. This tendency may depend on the movement and the hydrogen content of molten pool. Morevoer this may be interpreted by a view of probability which is assumed to be decided by the relative position of pore-molten metal interface for solid-molten metal interface.
The phase diagram and specific electrical conductivity of fused salt systems ZnCl2-SnCl2, ZnCl2-NH4 Cl and ZnCl2-SnCl2⋅2H2O, which are used generally as flux in soldering, were measured to clear a relation between the structures of these mixed salts and the spread area of Pb-Sn eutectic solder on copper base plate. The results obtained were as follows: 1) The diagram of ZnCl2-SnCl⋅2 system is a simple eutectic with no solid solution, and ZnCl2-NH4Cl system forms a intermediate compound formation with two simple eutectics. It seems the diagram of ZnCl2-SnCl2⋅2H2O system is a intermediate compound formation type. 2) The dissociation of ZnCl2-SnCl2 system was presumed as follows from the basis of J.D. Mackenzie theory on single zinc-chloride; 3ZnCl2→ZnCl64-+2Zn, 2+, SnCl2→Sn22++2Cl- 3) Isotherms of specific conductivity of ZnCl2-SnCl2 system deviate negatively from additivity when plotted against composition, and three partial negative deviations were found near the compositions of two eutectics and a intermediate compound in ZnCl2-NH4Cl system at just above liquidus temperature for each. 4) The transition temperature obtained from temperature.dependence of activation energy for electrical conductivity of ZnCl2-SnCl2 or ZnCl2-NH4Cl systems coincided with the temperature required for good spreading of the solder on copper plate, using these systems as flux. This result showed that an effective action temperature range of flux is from the liquidus to the transition temperature of itself and, therefore, a recommendable soldering temperature is limitted by these temperatures of flux to be used generally. 5) Th flux action of ZnCl2-SnCl2⋅S2H2O system could be explained as follows; SnC-l2⋅2H2O→SnCl2+2H2O ZnCl2+H2O→Zn(OH)Cl+HCl CuO+2HCl→CuCl2+H2O Although two equations of the latter were presented by H.H.Manko, the H2O produced by the dissociation of SnCl2⋅2H2O during heating reacts with ZnCl2 and forms HC1. The HO and SnCl2 act as flux in soldering of the range 180-350°C, and no SnCl2⋅2H2O acts as flux in the form of itself.
Mechanisms of beam (D-M) deflection observed in the cross sections of electron-beam-welded dissimilar metal joints were investigated. Explanations based on mechanical missettings or several physical characteristics were rejected through experiments. Finally, the stray magnetic field theory was evaluated. It was found that use of a magnetic shielding plate(having a small through-hole to pass the electron beam, a patented process of United Airecraft Corp., U.S.A.), which was placed parallel to and near the surface of the test plate to absorb the stray magnetic field, was effective to prevent the beam deflection. Application of inverse magnetic field parallel to the welding direction to cancel out the opposite-directional component of the stray magnetic field around the impinging point of the electron beam was also effective for the purpose. Thermo electromotive forces of several combinations of dissimilar metals were measured. It was found that. 1) When the thermo e.m.f. at 800°C was lower than 5.5mV, the beam deflection was hard to distinguish. 2) When the thermo e.m.f. went up higher than 5.8mV at 800°C, the beam deflection became recognizable, and the deflection became larger with the e.m.f. value. 3) The beam (and penetration) was always deflected towards plus (+) metals. It was concluded from these findings that, A) Hot and cold junctions are formed in welding dissimilar metals, and large electric current flows due to the thermo e.m.f. B) Stary magnetic field is formed in the upper space of the weld joint by this current. Interaction of the electron beam and a component of the field parallel to the welding direction deflects the beam to the transverse direction. C) The deflected beam produces an inclined penetration. D) The deflection angle a is to be proportional to ΔV800// √ E where ΔV800 is the thermo e.m.f. between two metals at 800°C and E is the accelerating voltage of the beam.
A new electrode called LBF62 was developed for improvement of toe geometry of fillet welded joint in 80 kg/mm2 high strength steel. Fatigue tests were conducted on specimens with fillet welded joint made by a new type of electrode, LBF62, and by the present type, LB62F, and the effect of improvement of toe geometry on fatigue strength was investigated. Ina ddition, the fatigue limits of specimens were estimated by using the test results in the previous reports, in which the effect of toe geometry on fatigue strength was discussed. The following conclusions were obtained: (1) Mean values of toe radius and flank angle measured in the specimen with fillet welded joint made by the new type of electrode were 4.4 mm and 32°, respectively. The value of toe radius was 4 times that measured in the specimen made by the present type of electrode and the value of flank angle was 20°smaller than that measured in the specimen made by the present type of electrode. (2) Fatigue limits of the specimen with fillet welded joint made by the new electrode were 13.0 and 21.1 kg/mm2 for the stress ratio of 0.6 and -1, respectively. On the other hand, fatigue limits of the specimen made by the present type of electrode were 10.7 and 15.4 kg/mm2 for the stress ratio of 0.6 and -1, respectively. Accordingly, the improvement of toe geometry by using the new type of electrode was very effective on the fatigue strength of fillet welded joint in high strength steel. (3) Grinding of toe surface affected the fatigue limit scarcely but nearly doubled the crack initiation life in the specimen made by the new electrode. (4) Estimated fatigue limits were in good agreement with the experimental values.
The effect of Si on transformation behaviour in synthetic weld heat-affected zone of steel was investi-gated using simplified steels made of pure metals and graphite. Si element did not almost influence ferrite transformation region in SH-CCT diagram for welding, and displaced slightly pearlite transformation region to a longer time and to a higher reaction temperature. Zw (Zwischenstufengefüge) rmat transformationregion was present on the side of very short time regardless of Si content, and existed to longer time in case of higher Si content. Cz' which is critical cooling time to obtain from SH-CCT diagram for welding could not measure because Cz' was too small. Cf' was a little influenced by Si, and it was small. Cp' and Ce' increased with Si content. In the region of middle cooling time (cooling time from A3 to 500°C; 6-60 sec), massive ferrite grew slightly large, and Zw precipitated easily with Si content. Morphology of Zw appeared that austenite between both ferrite sideplates or both rodlike ferrites decomposed to ferrite and relative large cementite. In the region of shorter cooling time (cooling time from A3 to 500°C; under 6 sec), ferrite grew to long ferrite sideplate and long needlelike ferrite by Si content, and morphology of pearlite was influenced by Si, too. Degenerate pearlite formation was difficult with Si, and the volume of pearlite was decreased by Si content increased. The hardness of martensite was not so influenced by Si. The hardenability curves in synthetic weld affected zone of steels raised with Si content, but Si above 1.0% did not influenced to the hardenability curves. heat-Though Si diplaced slightly longer the cooling time which hardness was rapidly decrease, it seems that Si dose not strongly influence to hardenability of weld heat-affected zone of steels.
Static tensile test was performed on base metal and weld metal of 1050 aluminum sheets, and investigation was made on the relationship between mechanical properties and solidification mode. Elongation of the weld metal was much less than that of the base metal, and decreased gradually as welding speed increased. This phenomenon was due to the growth mode of columnar crystals. Tensile strength, however, had almost the same value. Tensile cracks initiated mainly along grain boundaries of columnar crystals which were nearly normal to the tensile direction. The change of lattice strain and coherent domain size during tensile deformation was obtained by X-ray diffractometry. The lattice strain increased as nominal tensile strain increased, and the lattice strain in the weld metal had larger values than in the base metal. Initially the coherent domain size decreased abruptly and after that decreased gradually as the nominal tensile strain increased. In the weld metal the coherent domain size was less than in the base metal. Besides, the change of features of dislocations during the tensile deformation was observed with transmission electron microscope. The dislocations were multiplicated as the nominal tensile strain increased, and dislocation cell structure was developed. The dislocation cell structure was developed more easily in the weld metal than in the base metal. In the weld metal many discloations were observed near subboundaries which had been developed during solidification. When the tensile strain was 2.5% the size of the dislocation cell structure in the weld metal was about 2.5μ. This size decreased to about lμ when the tensile strain was 13%. The sizes in the base metal were larger than in the weld metal. The changes of the lattice strain and the coherent domain size were due to the change of the features of dislocations during the tensile deformation.
Influence of the mottled appearance on the tensile and bend ductility was investigated. The mottling frequently observed on radiogrphs of austenitic stainless steel weldmetals and castings. Longitudinal weldmetal specimens with different levels of contrast of the mottling were prepared. The results may be summarized as follows. 1. Progressive increase in the contrast produced a marked decrease in both tensile and bend ductility. 2. Cracks appeared on bend specimens were intergranular. The intergranular cracking strongly suggests that microfissures were present, while such specimens show pronounced mottling. The results seem to suggest that low density grain boundaries containing such a defect as microfissures may be important concerning the mechanism of the mottled appearance.
Previously, the authors proposed the method to calculate the grain growth during thermal cycle. That is, the thermal cycle is divided into small steps and the equation for isothermal-grain growth is applied to each step. By summing up grain growth on these steps, grain size during thermal cycle can be calculated. Then, it was confirmed that this method could be applied to various thermal cycles in commercialpurity nickel. In this report, as the next step, this method was applied to actual weld thermal cycles. Weld thermal cycles were measured in weld-heat affected zone of TIG arc welded (without filler metal) commercial-purity nickel of 2 mm thickness. Then, grain size in weld-heat affected zone was calculated. by applying above mentioned method to measured thermal cycles, and compared with measured grain size. Next, the course of grain growth and grain growth rate during weld thermal cycles were made clear using this method. Finally, effect of initial grain size on grain growth in weld-heat affected zone was investigated by this method.
The hydrogen induced fracture of HT80 steel was investigated by means of three-point bending test and electron fractography. The hydrogn induced crack manifests itself as the lowering of fracture stress and/or lowering of toughness by diffusion and accumulation of hydrogen towards the tip of notch or crack during incubation time. Based on the observation of fracture surface by ESM, the delayed fracture surface at high applied stress level showed dimple pattern and partially quasi-cleavage with more microscopic plastic flow, and with decreasing of applied stress, proportion of dimple pattern decreased, the other way, proportion of quasi-cleavage fracture increased. In the neighbourhood of lower critical stress, quasi-cleavage fracture with little microscopic plastic flow and intergranular fracture were predominant. The fracture morphology was explained to depend on the kinetics of diffusion and/or accumulation of hydrogen and the fracture surface of delayed cracking was different from cleavage fracture.