Microstructure of explosively bonded composites, low carbon-steel to low carbon-steel and austenitic stainless steel to low carbon-steel, has been investigated by transmission electron microscopy. The bond zone whose width is less than several μ consists of a mixture of a clad metal and a base metal, and the small crystal grains in each component metal are several thousand Å in size. Both areas within about 10 μ from the bond zone are composed of either small crystal grains or elongated grains of several thousand Å width. Dislocation density in these areas as well as the bond zone is of the order of 109/cm2. Larger crystal grains at distance of 10-600 μ from the bond zone has a dislocation density of 1010-1011/cm2, and the dislocation density at further increased distance is 109-1010/cm2. There exist tangled dislocations with cusps, dislocation loops and undeveloped cell structure. Thin deformation twins in austenitic stainless steel and elongated subgrains resulting from α→ε→α transformation of low carbon-steel are observed profusely. No significant hcp ε-phase is detected in the stainless steel. The adequacy of the proposed mechanism of the explosive bonding based on the theory of compressible fluid is discussed from the result obtained.
The purpose of this study is to make clear the effect of surface roughness of base metal on the spread area of both Pb-Sn alloy and BAg-8 filler metal in the capillary of mild steel plates. And also, this investigation was conducted regard to the spread area of water in the parallel capillary of silicate glass plates, in order to obtain some experimental data of relation between roughness effect of glass plates surface and the spread area of water in the glass plates capillary. These experiments were carried out as follows: These mild steel specimens with the capillary of 10×Hmm sectional area were dipped in the molten solder at 250°C or BAB-8 filler metal at 900°C' The spread area of these specimens were measured by planimeter. In addition, the silicate glass specimens with the cpillary of 10×Hmm sectional area were dipped in the water at 20°C, and the rising phenomena of water in the capillary of lgass plates were taken in the motordrived photograph pictured by one frame per minute rate. The results of these experiments were showed as follows: 1) The spread area of Pb-Sn alloy in the capillary of mild steeel plates with coarse surface was greater than that of one with smooth surface. This tendency was observed in the case of BAg-8 filler metal in the capillary of mild steel plates. However, these phenomena of filler metal did not showed in the case of large value of H. 2) As well-known capillary theory, the spread area of BAg-8 filler metal in the mild steel plates capillary with small value of H was greater than that of one with large value of H. The same result was obtained in the experiment of water-silicate galss plates capillary. But, the reverse tendency was observed in the result of Pb-Sn alloy mild steel plates capillary experiment. 3) Rising speed of water in the cpillary of silicate glass plates with the smooth sufrace, was higher than that of one with coarse surface.
The flux action of controlling flow and spread has little investigated for its difficulties in the quantitative measurement of spreadability. In this reports, stearic acid flux action of soldering was studied quantitatively on the relation between spreading of solder and the reaction of solder with flux. The resutls are summarized as follows: 1) The effect of heating time on the reaction of solder (Sn and Sn-Pb eutectic alloy) with Cu-stearate flux reconciled almost with that of heating time on spreading. 2) In the case of Sn solder, spread area increased linearly with the reaction of Sn with Cu-stearate flux. 3) Inorganic copper compounds (CuO, Cu2O, Cu(OH)2) reacted with molten stearic acid to give Cu-stearate. 4) The yields of Cu-stearate produced by the reaction of stearic acid with inorganic copper compound played an important role in spreading of solder with stearic acid / inorganic copper compound system flux.
In submerged arc welding of high tensile strength steels, it is positively demanded to produce weld metal having low crack sensitivity, especially hydrogen induced crack sensitivity. Agglomerated flux has many advantages, such as generation of more shield gas, high basicity and so on, but it has disadvantage of having a hygroscopic character. Meanwhile, it is generally believed that fused flux decreases the hydrogen content in weld metal on account of its unhygroscopicity. This is, however, not true because fused flux contains much hydrogen in flux itself in the form of OH radical, which is derived from the atmosphere of its manufacturing process. This investigation shows clearly that highly basic agglomerated flux, which generates plenty of CO2 gas in welding, can minimize hydrogen content of the weld metal. The effects of basicity, CO2 gas, absorbed moisture and dissolved hydrogen in flux on hydrogen content of the weld metal are quantitatively determined by a model of hydrogen dissolution mechanism proposed in this paper. The main results obtained are summarized as follows; 1) With an increasing basicity of the flux, the diffusible hydrogen in deposited metal decreases and the hydrogen dissolved into slag increases. 2) The diffusible hydrogen in deposited meatl steeply decreases with an increasing carbonate in flux. 3) Agglomerated flux has hygroscopicity, but that is lower than that of the low hydrogen type electrode coating. 4) Absorbed moisture of agglomerated flux completely evaporates at temperatures up to about 200°C. 5) In the case of the agglomerated flux about 20% of the air which has existed in the consumed particles of the flux enter the arc cavity and its ratio decreases to one third through generation of CO2 gas. 6) Only 0.015-0.020% of absorbed moisture in the flux enters the arc cavity, and its ratio decreases to one tenth when the flux generates CO2 gas. 7) Partial pressure of CO2 gas generated from the flux in the welding accounts for two thirds of total pressure in the acr acvity. 8) In the case of the fused flux, main source of the diffusible hydrogen in deposited metal is the hydrogen contained in flux itself in the form of OH radical.
This study was conducted as a preliminary research for further development of some plasma arc welding methods for thick plate above 10 mm. The large plasma torch and the control equipment designed to be proof against up to 1000 A with straight polarity connection have been fabricated especially for this study in our laboratory. With the ues of these equipments a series of experiments was carried out on the arc characteristics, welding conditions and welding sound. Conclusions obtained are summarized as follows: 1) Thermal efficiency of plasma arc is in range of 53-60% and its heat losses to cathode, nozzle, shield cover and the other parts are 2, 20, 9-11 and 7-11% respectively at 500 A arc current. 2) The Va-I (arc voltage vs. arc current), Va-Qp (arc voltage vs. plasma gas flow rate), and Va-la (arc voltage vs. arc length) characteristics of plasma arc at 300-500 A have been obtained as linear relationships whose slopes are in range of 0.02-0.05 V/A, 0.4-0.6 V/l/min and 0.4-0.6 V/mm respectively. 3) The optimum welding conditions for plasma arc welding of 6, 8 and 10 mm thick mild steel plates have been evaluated in connection with welding speed, welding current, and arc constricting wall length of nozzle. 4) In plasma arc welding of 16 mm thick mild steel plates, weld beads were produced as burn through or incomplete penetration beads. When the plates were backed up with copper plates, unstable plasma arc and sometimes series arcing occured and resulted in a defective bead. 5) The frequency characteristic evaluation of plasma arc welding sound reveals that welding sound consists of mainly 300 Hz frequency as fundamental tone and its higher harmonics due to current pulsating (300 Hz frequency) in full wave rectification, and also that frequency characteristic is subject to the influence of welding condition mainly in above 2kHz frequency range.
It is well known that welding produces thermal stresses which cause distortion of structures and residual stresses which influence buckling strength and brittle fracture strength of welded structures. Cold cracking of the weldment has beem investigated from a mechanical point of view with special attention paid to thermal stresses induced during the cooling stage of a welding thermal cycle. For a better analysis on these subjects, it is necessary to obtain more accurate information on the entire histories of stresses and strains to which the material is subjected during the process of welding. At the instant of welding, a limited portion of the welded joint such as the weldment and the base metal in its vicinity is heated to a very high temperature and therafetr cooled down to room temperature. The thermal cycle proceeds, the temperature distribution changes with time and the mechanical properties of the metals depend on temperature. In order to perform a more reliable analysis, the above mentioned factors should be taken into account. However, there are many difficulties in analysing theoretically practical models, including these effects, by classical methods, and there are only a few reports of their analysis based on simplified assumptions, such as regarding the problem as one dimensional problem or neglecting most of tempe-rature-dependent factors. The authors developed a method of theoretical analysis on this problem based on the finite element method, with consideration of the effects of changes in modulus of elasticity, yield stress and coefficient of expansion of the metal which are dependent on temperature under the assumption that problem is regarded as quasi-static, so that there is no interaction between temperature distribution and stress one. Accordingly, the temperature analysis is carried out independently before the stress analysis. As both analyses take incremental procedure, they can take into consideration of the effects of experience of the material before a stage at the following step of computation. if necessary, such as the rate of cooling on phase transformation, peak temperature on the mechanical properties, etc. in addition to the above mentioned temperature dependent properties. Examples of calculation given here are thermal stresses induced in butt welded joint under a moving electorode and local stresses and strains in RRC specimens during thermal cycle, and they show the usefulness of the method to general cases of welding.
In the welded joints, it becomes a common idea that the strength of weld metals is equal to or higher than it of base metal from the viewpoints of efficiency of welded joints. Otherwise, it is effective to use the weld metal whose strength is lower it of base metal in order to prevent the initiation of weld cracking. If welded joints having lower grade weld metal have larger strength than it required as the welded joints, it is one of the useful welding procedure to use the lower grade welding rod. In this report, the state tensile and brittle fracture behaviors of the welded joints having wled metal whose strength is lower than it of base metal—so called "Soft Welded joints"—are investigated. The example results of calculations about soft ratio and fracture toughness of weld metal required to guarantee the static tensile and brittle fracture strength which is almost equal to those of base metal were showed (Figs. 5, 11, 12, 15). In a case of production or selection the welding rod, a suggestion about tensile strength required as weld metals was made (Fig. 8).