The authors studied to find the most suitable grain size of the flux materials with which to coat the arc welding electrodes. Three kinds of fluxes respectively with five, two and only one material and five kinds of grain sizes, 200, 120, 70, 50 and 35 meshes respectively were taken. The coating of coated electrodes, welded conditions and some properties of all deposit metals were tried for investigation. Coating with large grains under 50 meshes was not satisfactory with regard to appearance and uni. formity. For some grains, many spatterings were found on the welded parts. Of mechanical properties, impact resistance was better for small grains, while tensile strength, and elongation were the highest for 70 mesh grain size. The authors concluded that small grains did not always give better properties, but that the range between 70 and 120 meshes or proper combination of grain sizes was most suitable.
As was stated in Report I, in the application of iron powder method to the cutting of cast iron, the cutting efficiency is greatly influenced by the grain size, carbon content and quantity of sprayed iron powder. This is attributed to the facts that different grain sizes and carbon contents of the iron powder make differences in ignition temperature and combustion velocity and that the efficiency therefore depends upon the appropriate spraying of the powder into the part of the flame at the highest temperature. The present paper reports of an investigation carried out to obtain the most desirable iron powder as flux by heating iron powders of different sizes and carbon contents in electric furnace and by checking the temperateres of ignition due to oxygen flow and combustion velocity. Further study was made to know the most desirable mixing rate of potassium chloride and aluminum powders with iron powder through investigation of the influence of mixing upon the cutting efficiency.
Ice flower like structure is formed in deposited metal. The purpose of this experiment i;s to seek for the cause of the formation of ice flower like structure by means of casting of core wire and some coating materials. The appearences of ice flower like structure which is formed in the casting specimens, are similar to those observed in the deposited metals. Namely, the fine columnar crystals are formed and the numerous micro-blow holes exist at the boundary of the columnar caystals. These structures can be seen by a microscope with magnification of approximately 25 diameters. The experiments are executed by the following procedures. In the atmosphere which contains water vapour, the core rods were melted in the Tamman tube, and the various elements were added to the molten steel, and then the molten metal was cast. The fractures of the casting specimens were observed after cooling. Ferro-silicon, ferro-manganese, ferro-titanium, -ferro-vanadium, metallic chromium, solid carbon and the oxides of these metals were added to the molten steel. The above experimental results are as follows. Ferro-silicon, metallic aluminium, metallic chromium and ferro-titanium were added to the molten metal of S-rod in the atmosphere which contained water vapour, and then these steels were cast. When the additional amount of the deoxidizer increase, ice flower like structure is formed(Fig.2). This is due to the following natures: the deoxi-dizing products, SiO2, Al2O3, Cr2O3 and TiO2 are refractory and their fluidity is low. When solid carbon, ferro-manganese and ferro-vanadium were added to the molton metal of S-rod and were cast, ice flower like structure was not formed. In the case in which Mn is used as a deoxidizer, MnO combines with FeO, and the slag of low melting point and good fluidity is formed. V composes the deoxidizing products with oxygen and also makes stable hydride with dissolved hydrogen in steel, therefore, ice flower like structure is not formed. It may be considered from these experiments that the existence of the deoxidizing products and the behaviour of hydrogen are the cause of ice flower like structure formation. In this experiment, the effects of cooling velocity, deoxidizing products and behaviour of hydrogen are considered to influence the formation of ice flower like structure.
The object of this investigation is to analyze the behaviour of hydrogen which is considered to be one of the causes of ice flower like structure formation. Steel exhibits a variable permiability for hydrogen, the solubility of which is much greater in molten steel at high temperature than in the solid steel at room-temperature. During the cooling process the steel releases hydrogen which is absorbed by the molten steel. The relation between the molten steel, hydrogen and oxygen was calculated theoretically and the amount of the dissolved, hydrogen in the metal deposited from various coated electrodes, was measured in accordance with the A. W. S.-A.S.T.M. hydrogen test. Figure 3 shows the relation between FeO and H; with the increase of oxygen amount, less hydrogen is dissolved in the molten steel. Among the same type of electrodes, those which result in ice flower like structure evolve more hydrogen than those which do not. For example, the ice flower like structure was not formed by A type electrodes which indicated the evolved gas less than 0.1cc/g. The dissolved hydrogen in steel in the equilibrium state is shown in Fig.8. Under I atmospheric pressure of hydrogen, steel absorbs more than 0.25 cc/g of hydrogen in the molten state, but precipitates the hydrogen when the molten steel solidifies, and leapes about 0.12 cc/g of hydrogen at B point. According to the above results, it is considered that the amount of the dissolved hydrogen in the deposited metal is above B point when ice flower like structure is formed. This large amount of the dissolved hydrogen is rejected through the boundary of the fine columnar crystals, and accordingly the micro-blow holes are formed, when the molten steel is solidified. And its appearance is just like the ice flower. Therefore, the micro-blow holes are formed by the dissolved hydrogen in the deposited metal, and it is considered that the amount of the dissolved hydrogen required to form ice flower like structure is larger than the amount of the dissolved hydrogen in the solid steel at the melting point under 1 atm.
1. Borax-alkali binder is classified in Borax-NaHCO3, Borax-NaOH, and Borax-KOH. 2. Borax-alkali binder used as welding flux, of which the proportion is such that addition of 40CC. water gives proper coating, develops best binding action, when about 2 g. of NaOH is added to the oversaturated solution of borax; namely, when NaOH concentration is around 1.25N, orKOH concentration is around 1.16-1.25N. 3. Depending on the kinds and proportions of welding flux, the binder proves most effective, with NaOH addition of less than 2g., when added water is less than 40C C., or when the solution is saturated for borax. 4. The principle of binding is the same either with borax-NaOH or with borax-NaHCO3. As Na-OH volume in the solution of the latter is very small as compared with the former, it can be assumed that this difference in NaOH volume is balanced by hydrolysis of NaHCO3 which takes place to compensate the loss of NaOH required for crystalization and precipipitation of dissolved borax.