The nitrogen content of arc-melted iron containing surface active elements, such as oxygen, sulpher and selenium, has been measured at various nitrogen partial pressures (N2-Ar mixtured gas). The surface active elements markedly increase the nitrogen content in arc-melted iron, and this nitrogen content increases semi-regularly with an increasing nitrogen partial pressure. For instance, in Fe-O system, the nitrogen content in arc-melted iron with under 200 ppm oxygen content in 5% N2-Ar atmosphere is a relatively low value such as about 300 ppm nitrogen. It is seen that the nitrogen content markedly increases with an increasing oxygen content in the range from 200 to 600 ppm oxygen in iron. These nitrogen contests are 3-10 times greater than the solubilities of non-arc melted iron. This anomallous nitrogen absorption has only been observed in arc melting and could not be explained by using the thermodynamical data on steel making reactions. On the other hand, it is known that FeO on the melt is formed in.the range of 200-400 ppm oxygen contcenration in the bulk. This oxygen concentration range also agrees with the range in which the nitrogen content in arc-melted iron markedly increases. This fact suggests that gas absorption mechanism would change as FeO is formed on the sufrace. A model of gas absorption mechanism in molten iron in arc melting was set up with the idea that the solubility of nitrogen in arc melting is not a true equilibrium value, but a steady state concentration between dissolution into and evolution from the melt. That is, the nitrogen is mainly absorbed through the atmosphere in arc which is in a highly activated state with a high chemical potential of nitrogen, and transported by fluid flow to the outer, cooler, region of the pool. Evolution of gas in the supersaturated outer regions is much affected by the state of its surface which is closely associated with the amount of surface active elements in the melt. When the surface of melt is covered with the surface active elements such as FeO, or FeS, the rate of evolution of gas will be extremely suppressed by FeO or FeS on the melt. Therefore, it is considered that the nitrogen content in the melt will become, higher than in non-arc melting.
In a plasma arc cutting, the behaviour of anode or cathode spots in a cutting kerf affects not only the distribution of heat input in the work piece but also the quality of the kerf or cut surface. Using a stack plate of water-cooled copper, the current in each plate was measured with arc voltage in order to clarify the fundamental behaviour of such a spot. Moreover, the spot motion in actual cutting was observed by an optical method, and analyzed from the correlation of the fluctuations between radiation intensity from the spot and arc voltage. Essentially, the sopt is carried away from the upper to lower side on the front surface of the cutting zone or the edge surface of the work piece due to the momentum of plasma and cold surrounding gas streams and due to the magnetic force acting on the spot and arc column. When the voltage between the arc column and the front surface of the kerf reaches a breakdown voltage, a new spot is suddenly made on the upper side. Consequently, the spot periodically repeats such a motion, so that the arc voltage fluctuates as sawteeth waves in several kHz to several 10 kHz corresponding to the spot motion. The above consideration shows that the wandering region of the spot is governed by the breakdown voltage of the sheath and the potential gradient of the arc column. Especially, effect of the former is considerably large. At reverse polarity, the breakdown voltage is higher than at straitgh polarity, because the voltage to make a new cathode spot can not be neglected as well known from the restrike phenomena in A.C. arc. Thus, the spot wandering regon at reverse polarity is extended in comparison with that at straight polarity. It is a noticeable fact that the cathode spot motion is remarkably affected by the condition of the plate surface and surrounding gas. If air mixing into the plasma stream increases, the cathode sopt seeks out an oxide film, and behaves the same as in cleaning phenomena at reverse polarity of TIG arc welding. Arc voltage, therefore, shows the characteristic triangle waves in several 100 Hz.
The mottled appearance frequently observed in radiograph of austenitic stainless steel weldments and castings has been investigated. The results may be summarized as follows. 1. It has been established that the X-ray diffraction causes the mottling. Diffraction theory (Bragg's law), however, does not explain the whole phenmena. 2. The relation between the incident beam angle and the mottling was obtained. 3. It was observed that the mottling was more pronounced on radiograph taken with a low voltage than on one taken with high voltage. 4. Solution treatment does not affect the mottling. 5. The mottling disappeared when the specimen was recrystallized.
There are some papers in which the possibility of sulphide gases and methane being yielded in steel weld metal is described but there is little experimental study about whether these gases may actually produce blowholes in steel weld metals or not. This experiment was carried out to clarify whether sulphur dioxide, hydrogen sulfide and methane gas exist in blowholes of steel deposited metal. The results obrained are as follows; 1) Very small amouts of sulphur dioxide and hydrogen sulfide were detected in an extreme case of deposited metal on a base metal containing high sulphur content 0.4% under CO2-12% H2 shielding gas 2) Methane was not detected even in an extreme case of deposited metal containing high sulphur content 0.4% under CO2-12% H2 shielding gas 3) Bolwhole gas in mild steel deposited metal by coated electrodes consists of i) mainly hydrogen and some amount of carbon monoxide and nitrogen in the case of using ilmenite type electrode ii) mainly nitrogen and some amount of carbon monoxide and hydrogen in the case of using low hydrogen type electrode.
It is well known that the effect of longitudinal magnetic field on weld zone causes a turning of arc column and a turbulance of mloten pool. That is to say, magnetic stirring is generated. The influence of the magnetic stirring on the weld zone in the case of TIG or MIG welding has already been reported. According to the reports number of blowholes decreases, and reduction of grain to small size and improvement of welding speed can be expected. But the result in the case of Submerged-arc Welding has not been reported yet. This report investigates the influence of magnetic stirrig on the weld zone by Submerged-arc Welder with magnetic equipment. The results obtained from these studies are as follows: 1) The bead becomes wider up to a certain strength of magnetic field, but it becomes narrower again when the magnetic field strength exceeds a certain limit. 2) The depth of penetration also shows the same tendency as the bead width. It becomes shallower up to a certain limit. 3) The heihgt of reinforcement increases in proportion to the degree of magnetic field strenght. 4) The average sectional area of bead does not change so much. 5) Magnetic stirring minimizes the primary crystals of weld metal. But their minimization has a certain limit. It cannot be minimized beyond the limit.
Several experiments concerning the maximum arc length were carried out as the basic research for the stabillity of the electric arc in welding. But reports on this type of study under windy conditions have apparently not been published to date. In this paper we describe an experimental study of the variation of the maximum arc length under various windy conditions and the influence of the wind on the vaporized coating of electrode. The results are summarized below: 1) The maximum arc length is affected remarkably by the coating of electrode and the arc length of an ilumenite type is greater than that of a low hydrogen type. It is assumed that the vaporized coating, i.e. gas molecules, is more effective on striking the arc than the vaporized core metal and moreover the former depends strongly on the wind conditions. 2) As the wind velocity increasse the maximum arc length decreases as a whole and each length evidently tends to be constant independently of the welding correct. Changing the angle of electrode, the maximum arc length under windless condition becomes the greatest at 90°angle of electrode, but at a wind velocity of 4 m/sec or 9 m/sec it does so at 45°angle. 3) The value of the arc angle does not agree with that of the angle of electrode and usually the former is larger than the latter. The difference of each angle becomes large while the angle of electrode will be small. Below 45° angle of electrode there is a little effect of the wind, but above this angle, especially at 67.5°, the arc angle is clearly influenced and approaches the angle of electrode. 4) The arc voltage and current at a moment of arc-vanishing depend on the angle of electrode. With an increasing welding current, the arc voltage decreases and the current increases. The former is affected by the wind direction but the latter is not affected very much. 5) The results suggest that the interaction between the wind and the gas ionic flow of the coating and the relation between the arc length and the angle of electrode are the subjects for the future study.
Steel pressure vessels of light-water cooled nuclear power reactors are constructed with stainless steel weld overlay liners on their inner wall. Occasional cracking in the stainless steel cladding of pressure vessel is considered one of the problems in the development, and also maintainance, of the reactor in several countries including Japan. Since the stainless steel overlay cladding is subjected to thermal and internal-pressure loads in reactor operation, it is desirable for the cladding to have high strength and ductility from the standpoint of structural safety. In Section III of ASME Boiler and Pressure Vessel Code, post-weld heat treatment of more than one hour per inch at over 1100°F (593°C) is required for the weld joints of low-alloy pressure vessel steels. This heat treatment to relieve residual stresses in the weld joints during construction of the pressure vessel is considered to cause sensitization of the cladding. The purpose of the present study is to obtain information on the effect of post-weld heat treatment on the mechanical properties of overlay weld. The tests used include half size Charpy-V notch impact test, micro tensile test and guided side bend test. The test specimens were machined from the overlaid cladding, weld-bond and base metal heat treated at 600°, 625° and 650°C for 20, 50 and 100 hours. From the results obtained, the following conclusions are drawn: (1) The decrease in ductility occurs in overlaid cladding or weld-bond, depending on the post-weld heat treatment applied. A remarkable decrease occurs in the impact property of overlaid cladding; while a considerable decrease, in tensile and bend properties, was observed in the weld-bond. (2) The post-weld heat treatment should be limited to within 20 hours at 625°C, because of an excessive decrease in ductility caused in the weld-bond by prolonged heating. (3) In order to reduce the embrittlement of overlaid cladding due to post-weld heat treatment, the Gow and Harder's empirical ratio K (%Cr+4×%Mn+3(%Si-1)-16×%C/%Ni+1/3(%Mn-1)), Cr/Ni ratio and ferrite content in Schaeffler's diagram should be limited to below about 1.9, 2.1 and 7.5% respectively.