Temperature variation in infinite wide plate is treated from the standpoint of heat conduction theory in 1, 2, 3 dimensions when stationary heat Q is supplied instantly at the time t=0 as well heat q cal/sec is supplied for duration 0-t. The treatment is limited only to one dimensional case for distributed heat supply. Heat loss from the surface is neglected and the thermal constant is assumed to be constant independent of temperature.
The temperature dependence of deformation properties of welded joints was investigated by means of the photoelastic coating technique. A smooth tensile specimen with a buttwelded joint was used to study the micro-structural dependence of plastic behaviour of a mild steel. From successive developments of photoelastic fringe patterns obtained in tension tests at various low temperatures, the structural and temperature dependence of yield strength of such parts as parentmetal, heat-affected zone and weld metal was determined. It was found also that the yield strength of the heat-affected zone was higher than that of the parent metal or the weld metal in the range from room temperature to -196°C. The existence of such a harder metal as the heat-affected zone produces a plastic constraint in a softer metal, on which the former borders, and then it hinders the trarsverse contraction of the latter and leads to the embrittlement in theconstrained regions. The temperature dependence of plastic constraint was also discussed.
Several noteworthy investigations of temperature distribution in spot welding have been reported; especially, Greenwood calculated temperature distribution during spot welding taking into account the actual geometry involved, but neglecting the effect of contact resistance. Furthermore, he andothers measured experimentally temperature distribution in spot welding by metallographic method, and compared the results (it is possible to find temperature distributions of 730°C, 900°C, 1050°C and 1450°C by the metallographic method) with the results theoretically obtained. From this comparison it was generally concluded that in early stage of spot welding the calculated temperature distribution did not resemble the experimental one, but at a later stage this was reversed. On the other hand, the authors calculated temperature distribution in a one-dimensional model that simulated spot welding, replacing the effect of contact resistance intoa temperature rising part of band shape in initial stage of heating, and found that contribution to nugget formation originated in contact resistance might be almost neglected in thetime of nugget formation, compared with contribution originated in bulk electric resistance, in the case of spot welding thin sheets. Anyway, details of temperature rise in the initial stage of spot welding are unknown, and there is a complete lack of concrete information on how oxide layer between welded sheets begins to breakdown, and how subsequently the temperature in the welded part rises. The authors developed a new measuring technique (FH-method) for temperature distribution in a two-dimensional model that simulated spot welding geometry at an earlier stage, by combination of the temperature indicator with high speed photography. This technique makes it possible oflserve in detail, the breakdown of oxide layer between the sheets and the subsequent temperature rise, and therefore can give a valid means for making clear spot welding phenomena. In this report, authors study influences of the electrode force and the electrode shape on temperature patterns and factors which influence unsymmetry of the initial temperature distributions.
Welded region, usually on which the maximum residual stress has been induced in welded structures, shows a hardened structure and must be subjected to structural changes during stress relief heat treatment. This changes may cause a different relaxation property of welded region from base metal. In order to clarify the influence of welded region upon reduction in stress in the heating stage, various types of H-type restraint specimen were subjected to low-temperature heat treatment. Thermal expansion measurement and X-ray diffraction test on welded region were also carried out to identify the structural changes. The obtained findings are as follows. 1. Reduction in residual stress took place on heating stage over than 250°C and was small in the holding stage. In accordance with this stress reduction, tensile plastic strain occurred. 2. With the existence of pre-stress-relieving at 620°C, reduction in stress as well as plastic strain did not take place on heating stage lower than 400°C. This means that pre-stress-relief retards reduction in stress by its stabilizing effect. 3. Deposited metal and synthetic heat affected zone showed a peculiar expansion at 250°C and thereafter only on heating. This peculiar expansion phenomenon became noticeable with decreasing cooling rate from 1350°C in the heat affected zone. 4. X-ray diffraction tests indicated the existence of retained austenite in deposited metal as well as in synthetic heat affected zone. Volume of retained austenite in synthetic heat affected zone increased with decreasing cooling rate from 1350°C. 5. A small precipitation was found in deposited metal after heat treatment over than 300°C. 6. Enhanced reduction in stress in welded region would be attributable to the lowered resistance for plastic deformation, that is, strain field introduced by both quenching and precipitation as well as by phase change.
As stated in the previous paper, there found two kinds of the cathode modes, i.e. the cold and hot cathode modes, in a low pressure arc generated between the graphite electrodes. Consumption of a graphite cathode was quite different in each cathode mode. For example, a carbon vapour stream and spattering from the cathode root were ovserved in the cold cathode mode, while no vapour stream nor spattering was seen in the hot one. The consumption characteristics of a graphite cathode and the corelation to the cathode mode were investigated to clarify the cathode mechanism. Experiments were conducted on an arc with a graphite cathode and a water cooled copper anode under the condition of the current range being 10-120 Amp and of the pressure 10-100 Torr of hydrogen and 10-60 Torr of helium and argon. Results obtained in this study are as follows. (1) In addition to the cold and hot cathode modes, anew mode which was termed the plasma cathode mode was distinguished in a C(-)-Cu(+) arc at low pressure, regardless of the kinds of gas. This mode which was featured by a bright sphere in front of the cathode tip (cathode plasma ball) appeared as an intermediate stage of the cold and hot cathode modes. The existence of the plasma cathode mode was clearly recognized in the consumption characteristics of a graphite cathode but hardly detected in the electric characteristics of an arc. (2) A cathode plasma ball expaoded its size with the increase of current or the reduction of pressure. In the plasma cathode mode, it was clearly separated from the arc column by a dark space. When the dark space became undetectable, the hot cathode mode emerged. (3) Under the condition of this experiment, specific consumption rate mG/I (mg/A min) of a graphite cathode ith the cold cathode mode was as hifih as five times or compared with so the one in the hot cathode. Meanwhile, in the plasma cathode mode, mG/I was a little higher than that in the hot one. In the cold cathode mode, more than 90% of the consumption was the sublimation of carbon at the cathode root, and the spattering loss was less than 10%. (4) In the cold cathode mode, carbon rather than the ambient gas might be preferentially ionized in the cathode fall region. (5) The transition of the cathode mode was determined by the systematic study of the consumption characteristics of a graphite cathode. In this study, three governing factors of the cathode mode(p, I & Vi), which were mentioned in the previous paper, were clearly proved.
Microscopic survey, measurement of grain size and electron probe microanalysis of Fe-Ni, Fe-Cu, Fe-Mn and Fe-C weld metals were performed. The results obtained are summerized as follows; (1) In Fe-Mn, Fe-Ni and Fe-Cu weld metals, the solidification structure changes from equiaxed to columnar crystal and still to cell structure with increasing the contents of alloying elements. (2) In Fe-C weld metals, the solidification structure changes from equiaxed to columnar crystal with a small amount of carbon. (3) The segregation of alloying elements are observed in the cell boundaries. (4) The solidification structure of the weld metals is disarranged by peritectic reaction. (5) The concentration gradients of alloying elements are observed in the weld metals of 26 to 108 μ width near the fusion lines. (6) The alloying elements appear to diffuse into unmelted base metal about 5 to 10 μ. (7) The macroscopic segregation of alloying element is observed only in Fe-Ni weld metals.
In the previous report, the recovery of hardness in H.A.Z. of commercial Al-Zn-Mg alloy containing Cr and Mn was examined in details. In the case of welds on T6 treated materials, the region where partial reversion had occurred during welding was the weakest part in H.A.Z.. This phenomenon seems to be due to the existence of Cr and Mn in specimen. From this point of view, this paper deals with pure Al-Zn-Mg alloys. X-ray small angle scattering method and thin foil electron microscopy have also been used to make further investigation about the problem in H.A.Z.. The results are summarized as follows; (1) T4 treated materials consist of G.P. zone (10-15 Å radius). T6 materials consist of G.P. zone (about 30 Å radius) and η' phase at boundaries or sub-boundaries. (2) In the region where perfect reversion had occurred, the recovery rate of hardness became larger as Zn content increased. Mg enhanced the value of hardness immediately after welding. Inculaticn time was recognized in the material containing Cr and Mn. (3) In the weakest part in H.A.Z. of welds on T6 treated material, partial reversion occurred and G.P. zone had a tendency to resolve as peak temperature increased. The coarsening of η' phase could not be ascertained, but the distribution of partial reversed G.P. zone was sparse. (4) The width of H.A.Z. of welds on T4 treated material was larger than that of welds on T6 treated material in the case of constant heat input. This phenomenon is related to the fact that the size of G.P. zone in T4 treated material is smaller than that of T6 treated materials