Fracture strength in 80 kg/mm2 steel and mild steel joints was examined at low temperatures, usingtransversely-welded wide plate test specimen and small size specimen notched in heat-affected znone. 1) The fracture strength of butt joint decreases with decreasing temperature, and the relationship between logarithmic strength values andtemperature is linear. 2) The local stress raisers, such as reinforcement or undercut, are necessary to lower down the strength of joint. And their equivalent crack length is about 1.6 mm. 3) Pre-loading techniqe take good effect to the strength of joint at lower temperatures, but the residual stress gives no effect to it. 4) The sufficient correlation between the fracture toughness value of heat-affected zone and the fracture strength of joint was obtained.
The electrical and thermal characteristics of tungsten arc under axial gas flow in argon atmosphere of 18 to 760 mmHg are examined and various penetration shapes formed in the specimens of copper, aluminum, mild steel and stainless steel at the above mentioned ambient pressures are discussed in relation to the arc characteristics. The facts elucidated are as follows. 1) At reduced gas pressure, elliptical "Cathode Zone", which is highly ionized and has a higher energy density compared to the arc column, is deformed to the conical shape by the axial gas stream. Arc voltage is considerably high in this case. 2) The velocity of axial gas stream increases with decreasing gas pressure and with increasing arc current. In our equipment, it becomes larger than the sound velocity under the gas pressure lower than 100 mmHg. 3) Under axial gas flow, two types of arc exist, namely "H Type" and "L Type". "H Type arc" has a higher arc voltage and in this case arc is kept at the tip part of the cathode electrode. On the other hand, "L Type arc" has a lower arc voltage and the arc covers much area of the cathode electrode. 4) At reduced gas pressure, potential gradient of arc column in "H Type arc" is nearly equal to that in "L Type arc" and is larger than that in the arc in statistic atmosphere. The sum of anode drop and cathode drop, VA+VK, in "H Type arc" is higher than that in "L Type arc". The difference of VA+VK between two types is presumed to depend on the surface condition of the cathode electrode. 5) At reduced gas.pressure molten metal is rapidly removed by the strong gas stream. As a result solid groove is formed in the metal specimen. It must be mentioned that when the cathode zone touches to the specimen, the contact zone at the specimen melts very rapidly. In this case deeply arc-gouged or sharply arc-cut groove is formed. The width of the groove corresponds to the contact diameter of the cathode is zone on the specimen.
Mild steel and stainless steel were welded in controlled arc atmospheres. Effect of nitrogen partial pressures in the welding atmospheres of N2, N2-Ar, N2-O2, Air, N2-CO2 or N2-H2 and welding polarity on the nitrogen content of weld metals was systematically studied. The main results obtained are summarized as follows: 1. The nitrogen content of weld metals made in neutral or reducing atmospheres such as N2-Ar or N2-H2 increases with the increase of the partial pressure of nitrogen. 2. The co-existence of oxidizing gas with N2 in the arc atmosphere increases greatly the nitrogen content of weld metals. 3. Anomalous absorption of nitrogen was observed at low pressures of the arc atmospheres. 4. The nitrogen content of mild steel weld metals made in N2, N2-Ar, or N2-H2 welding atmospheres is not influenced by welding polarity, while the nitrogen content of stainless steeel weld metals made with DCSP is more than that with DCRP. 5. In oxidizing atmospheres such as N2-O2 or N2-CO2, weld metals absorb much more nitrogen with DCRP than with DCSP.
Further study is made using three types of circuit shown in Fig. 1, because the arc plays an important role in flashing action. Oscillograms of flashing current in late stage of flashing process using three circuits are shown in Fig. 3. In the case of circuit I, the arcing current is held to continue for comparatively long duration by large leakage inductance of welding transformer (L0) In the case of circuit III, however, the arcing current decreases rapidly, because the arc energy is only supplied from the stored energy in the small inductance L. This means small heating per one arc. The short circuit current increases rapidly for circuit III for the same reason mentioned above. The rapid increase of short circuit current is effective to break the newly formed short circuit path due to the local concentration of joule's heat. The above mentioned characteristics concerning circuit III result' in frequent splashing of many droplets of small sizes under the same platen velocity as that in circuit I. Circuit characters affect the formation of molten metal layer in flashing period. In the case of circuit I, the molten metal layer is observed to locate on a part of test piece end. It is supposed that the molten metal on the central part is splashed off by powerful arc force. But, in the circuit II or III, molten metal layer of 0.5-0.2mm thickness is observed all over the end of test pieces. Thus, if the molten metal layer is formed all over the end of test pieces by selecting the circuit constant, welds with good mechanical properties are obtained, even though upset current is not allowed to flow by cutting off artificially the power circuit as soon as upsetting begins.
Byx-ray diffraction technique the conditions for origination and the crystallographic chracteristics of the new columnar crystal (that is, stray crystal) in TIG weld bead have been investigated using single crystal of commercially pure (IS) and 99.93% pure aluminum 1 mm thick sheets. Conclusions obtained are as follows: (1) Origination of new columnar crystal which was called as "stray crystal" by authors was confirmed by means of TIG bead-on-plate welding on single crystal of commercially pure aluminum sheet. (2) Stray crystal originates when the direction of the maximum temperature gradient at the solidliquid interface of the columnar crystal growing from the fusion boundary deviates from the nearest ‹100› direction by 40-50 degrees. (3) The origination of the stray crystal is seen to be related with the purity of the material. Namely the decrease of the purity in the base metal genarally urged the origination of the stray crystals in the weld bead (4) A ‹100› direction of the stray crystal usually coincides with the direction of the maximum temperature gradient at the originating interface. Moreover the subgrains inside the each stray crystal are parallel with a ‹100› direction.