When the stored energy of an electrolytic capacitor of the spot welder is discharged through the primary circuit of the welding transformer by providing an electromagnetic switch, electrical phenomena such as high frequency oscillation or arc appear between the switching contacts. Though the high frequency oscillation is due to an electrical cause, the arc is attributable to the mechanical chattering of the contacts. The modes of arc occurrence are analyzed and the mechanical chattering of contacts is rendered visible by means of oscilloscope. The theoretical consideration of the chattering mechanism showing that the contact chattering is reduced by min imizing the momentum of the moving part of a switch and the contact gap length as well as by increasing the contact force, is verified by a series of experiments.
A series of tests was performed to investigate the effect of high temperature prestraining on the notch toughness of a rimmed steel plate, 25 mm thick, by using standard V-Charpy specimens, and also, on the behaviours of the fracture stress curves by using the notched bar tension specimens. As the result, a harmful effect was marked conspicuously in 15 tf-lbs and 50% shear transition temperatures after prestraining at 200°C or 300°C. The value of Tr15 became about 75°C higher than that of the base metal after prestraining by 10% at 300°C. Less adverse effect was recognized by prestraining at higher temperatures, and at 500°C embrittlement was hardly observed after prestraining. Moreover, the role of aging was investigated by comparing the effect of high temperature straining followed by heating at the prestraining temperature with that of aging after room temperature prestraining under various heating times, and it was found out that the part of the embrittlement, caused by excess in high temperature prestraining as compared with room temperature treatment, was of the non aging-type one and the remaining part was due to strain-aging. As a whole, it was suggested after examining the behaviors of both cleavage and fibrous fracture stress curves that the phenomena of embrittlement of steel caused by high temperature prestraining ought not be discussed from the results of the retained ductility tests but from those of the notch toughness tests.
In welding of stainless clad steel, the stainless steel deposits are diluted by fusion and mixing of the base metal. But the relation between dilution and welding condition is not made clear up to date, which fuct has been a considerable inconvenience to welding practice in this field. In this report, this relation was derived by such calculation method as was used in the research of weld penetration contour. It was confirmed that there was a reasonably good agreement between the calculated data and experimental results
The diffusible, residual and total hydrogen contents were determined with all weld stcel which was deposited by CO2-O2 arc welding process in the copper mould and quenched in water. A simple apparatus with the Töpler pump was used for the vacuum-heating determination of the residual hydrogen content. The heating of sample was done at 600°C. The experimental results obtained are as follows: 1) Although the hydrogen content of all weld steel gradually decreases with desiccation of supplied gas, if the dew. point of supplied gas is lowered to the range of -40--50°C and below, then the hydrogen contents are almost the same ; the content of total hydrogen 2.5-5cc/100g, that of diffusible hydrogen 1-2.5cc/100g and that of residual hydrogen 1-3cc/100 g. 2) This fact shows that when a super-dried shielding gas is supplied, the humidity of the atmosphere has an effect on the hydrogen content of weld metal in this country, in which it is humid, especially in summer. 3) In gas-shielded metal arc welding, the hydrogen content of electrode wire may have an effect on that of weld metal. 4) The hydrogen contents of all weld metal determined in this experiment may be able to be compared with that measured in steel-making. According to some reports, the lowest hydrogen content of weld metal in this experiment is nearly the same as the lowest value measured in steel-making.
In the previous paper (1), it was reported that some extreme low fatigue strengths of weld joints were experienced as the result of the stress concentrating effect of a notch (incomplete penetration), in case where this notch was oriented perpendicularly to the direction of load. The necessity was felt of investigating the effect of other factors than stress concentration, such as a metallurgical defect existing at the root of a weld. This paper is mainly concerned to a factor aD, which may represent such metallurgical effect. Specimen was welded to have a notch in butt weld, which was parallel to loading direction so that the notch shape itself might not affect the stress concentrating effect. Fatigue test was performed using such specimens, and approximate value of an was presumed after analysing the results.