As the first step of the research on oxy-acetylene gas cutting, the authors measured the cutting speed under the same cutting pressure, thickness of plate and standard drag, using the controllable-speed gas cutting machine ; fitted No. 2 blow-pipe with No. 1 nozzle (1 mm dia.) and found the oxygas volume necessary to cut a meter length of the plates. Then the relation of the length of visible gas stream to cutting efficiency of blow-pipes was clarified and the tentative design and manufacture of a divergent nozzle with ρ the increasing ratio of cross-sectional area of nozzle was carried out and comparison made between cutting efficiency of this nozzle and that of a straight nozzle. It is concluded that the length of visible oxy-gas stream of a nozzle can be regarded as representative of cutting efficiency and gas cutting speed can be raised 10-15/ with the divergent nozzle as compared with the straight one. Further, there is a critical cutting pressure for increase of cutting speed to the diameter of nozzle, the value for 1.0 mm dia. being 5 kg/cm2.
The mild steel covered arc-welding electrodes marketed in Japan are slag shield type of which the chief ingredient is ilmenite (FeO. TiO2). They have been developed remarkably since before World War II, the number of brands, submitted for official approval, ten years. The results of mechanical tests upon them can be classified into three categories in the following table, is e., class I, accounting for 16.5%; class II, 38%; and class III, 18.50, having no connection with the kind of the core wire. Next, the author discussed on the heterogeneity of deposited metals, citing the difference of me. chanical test values of two test pieces taken from one deposited metal specimen, and proposed the allowable limit of these deviations as follows: Tensile strength, 3.7 kg/mm2 and elongation, 12.2 % for tensile test. Charpy impace value, 4:5 kg-m/cm2 for inpact test.
To specify the notch-toughness of materials, so-called transition temperature is, used as a criterion with the general belief that the characteristics of notch-toughness cannot be evaluated to ordinary mechanical tests such as tension test, etc. In the factory, however, it will take great labor to obtain the transition temperature of materials. From this point of view the authors have carefully studied the relation between ordinary tensile test results and U-and V type standard Charpy test results within the temperature range -80°C to +200° using four Japanese representative rimmed steels (see Tables I and II).The characteristics of the tension test results at low temperatures are shown in Figs 7-13. From these, of course, it is difficult to specify the notch-toughness of materials. Then φ or φ' was defined which represents the measure of strain hardening to ultimate point from origin or yield-point as follows: φ=actual ultimate point stress/ultimate point strain φ'=(actual ultimate point stress) - (yield-point stress)/ultimate point strain (see Fig.20), where actual ultimate point stress, ct and strain, εt are calculated by the area apart from local shrinkage portion after breaking, according to Mc Gregor (refer to the notations in Sect. 5). As to the value of φ or φ' the following characteristics are notable: a) φ or φ' value is constant within the temperature range of -80°C to +100°C and the value increases as the temperature is raised above +100°C (see Figs 18 and 19). b) The relation between the transition temperature determined by Charpy test and φ or φ' within the temperature range of -80°C to +100°C is shown in Fig.22 or 23. From them, it is clear that the material of which φ or φ' value is the smaller shows the lower transition temperature. Thus φ or φ' may be taken as an index of the notch-toughness of materials.
In the case in which two bodies are joined together, the natural frequency changes according to the degree of joining. In view of this fact, the authors considered it possible to presume the strength of spot weld by measuring the natural frequency of spot-welded materials. Theoretical study and experiments were conducted with materials of super-duralmin.It was ascer-tained by this that the theory coincides with the experimental results.
In the present experiments gas welding of nodular graphite cast iron (3 kinds of Cu-Mg, Fe-Si-Mg and Ca-Fe-Si-Mg system by casting methods) was mainly carried out supplementarily with remelting and casting experimentations of the same samples. Concerning gps welding: 1) In order to take full advantage of the high toughness of this cast iron, the structure of welded parts was made as near as possible to the nodular graphite structure of mother plate. This was accomplished by using welding core of same material and other cast iron and adding some Mg alloy to welding flux. 2) Welding was done by heat treatment so as to avoid the chilling and marternsite tendency of welded parts. 3) Mg alloy addition to the flux was found useful in developing graphite spheroids. 4) The results were compared with the data obtained from operations with other than the above non-castiron welding cores. Concerning remelting-casting experiments: 1) Tendency of disappearance or fine-graining of graphite grain under heating temperature, of this cast iron and tendency of chilling effect with varying cooling velocity were observed to know roughly the cooling-speed effect on appearnce of spheroid graphite and chilling in welding. 2) Under the heating temperature of gas welding, some of the graphite grains become finer, but others remain to grow during the cooling process. 3) At the cooling speeds of weld metals, around 6°C/sec or less, (temperature range of melting point-A1 point), chilling did not occur.
In the preceding papers one of the authors stated that nitrogen in the weld metal would have a noticeable effect of disturbing the systems of weld metals and that the cooling speed had little effect on the activation energy for stressrelief in the case of hand-welding. This time the authors used the unionmelt weld metals as the specimens observing the activation energies to prevent the personal errors in welding from influencing the state of weld metals, and to keep the welding conditions constant. As a result of testing they reached the following conclusions: 1) Mn has little effect on the activation energies for stress-relief. 2) C, Si and P etc., have great influences, i. e., they increase the activation energies of weld metals and tend to greatly disturb the ferrite structure system in weld metals.