The authors performed a study on fatigue in the weld metal and heat-affected zone of mild steel using V-notched specimens subjected to plane bending and found that the fatigue cracks in the weld metal and heat-affected zone propagated along the grain boundary more remarkably than those in the base mtal. The study was carried out to clarify the relationships between the respective microstructures of the welded part and the mechanisms of the propagation of fatigue cracks. The metallographic observations of fatigue cracks on the notched specimens taken from the base metal, the weld metal and the heat-affected zone of SM41 welded were performed under stress level a little higher than fatigue limit of each specimen and the following results were obtained. 1. More precipitates, which were identified as cementite by electron diffraction, were found at the grain boundaries in the weld metal and heat-affected zone than in the base metal. By transmission electron microscopy, no precipitate could be found in the grains of the fine grained zone, the spheroidized zone and the base metal, while carbons seem to hava precipiated on the dislocations in the weld metal and the embrittled zone. 2. It was found that the fatigue cracks in the heat affected zone propagated along the grain boundaries more frequently with an increase in the amounts of carbides at the grain boundaries.
Recently, the demand for constructing welded structures for low temperature materials such as LPG, LMG, liquid oxygen and nitrogen has increased. Low temperature structural steels such as aluminum killed steel (QT), 2.5, 3.5 and 9% Ni steels have been employed for these structures. The brittle fracture initiation and arresting characteristics of these steels are very important for their application. It is wellknown that the thinner plate has the lower transition temperature on account of the decreased triaxiality and the improved metallurgical factors such as the fine grain and the lower finishing temperature, etc. In this paper, thin mild steel plates or sheets were investigated to evaluate the brittle fracture initiation and the arresting characteristics by using the large size tests such as the deep notch test, the welded and notched wide plate test and the ESSO test with temperature gradient. Two scmikilled steels and two killed steels 3.2 mm thick were tested. The brittle faacture characteristics of plate in the directions parallel and nomal to rolling were investigated. From the results of these large size tests, the excellent notch toughness or brittle fracture initiation and arresting characteristics were proved. In addition, the effect of welding residual stress on brittle fracture initiation characterestics was discussed.
We discussed the embrittlement of 80 kgl/mm2 class high strength steels which occured when they were immersed in a 0.5% acetic acid solution saturated with H2S at the temperature of 35°C, and about the effect of immersion in this solution on the time to failure of sulfide corrosion cracking. When test pieces were immersed in the solution, the elongation and reduction-of-area diminished with immersion time, but the yield stress and tensile strength did not practically change. The test pieces which had become brittle by sufficient immersion in the solution recovered their ductility by ageing at 50°C. As this phenomenon occurs by discharging of absorbed hydrogen during the ageing, it is confirmed that the embrittlement occurring in the solution is due to the diffusible hydrogen absorbed in steel. The volume of hydrogen absorbed in steel increased with immersion time in the first stage of immersion, but after very long immersion it decreased with immersion time because of the lowering of corrosion rate due to the disturbance by the accumulated corrosion products on the surface of test piece. Time to failure, grew shorter by the immersion of test piece in the above solution before sulfide corrosion cracking test. The differences in time to failure between as-received pieces and immersed pieces became larger with a decrease of applied stresses, though the periods of immersion were the same (48 hours). When the applied stress was 20kg/mm2, the difference increased up to the value of 12300 minutes. In the region of applied stress below the value of 45kg/mm2, the time-to-failure of test pieces which were aged at 50°C after the immersion coincided nearly with that of the as-received test pieces. But in the region of applied stress above the value of 45kg/mm2, they did not coincide with each other. Judging from the above fact, it was estimated that the shortening of the time-to-failure of immersed test piece in the region of applied stress below the value of 45kg/mm2 was mainly due to the diffusible hydrogen absorbed in steel during the immersion.
To improve the toughness of electro-gas weld metal, several kinds of electrode wires with various contents of aluminum and molybdenum were prepared. Weld metals of 20 mm and 32 mm low carbon steel plates using these electrode wires were examined for mechanical properties, microstructure and non metallic inclusions. 1) A microstucture of electro-gas as-welded metal containing aluminum and molybdenum is finer grain than that of as-welded metal containing only aluminum. And the impact value of the former is higher than that of the latter. 2) A small aluminum content improved the fatigue strength of weld metal but a higher content did not. 3) A chain or film of sulphide inclusions was observed by an electron-microscope in the weld metals of a relatively higher aluminum content.
In order to prevent the weld metal of rusted, painted or oiled steel plate experiments of CO2-O2, CO2. Ar-O2 and Ar-CO2 arc welding were carried out using the electrode wires with various contents of deoxidizers, especially a fairly large amount of aluminum. As the result, it was experimentally concluded that an aluminum content over 0.35 per cent of electrode wire was effective to prevent the porosity in the weld metal of rusted, painted or oiled steel plate Moreover, the experiment on the influence of wind on porosity showed that the electrode wires containing aluminum were effective to prevent the porosity, even when gas shielded arc welding was carried out in the wind with 1 to 2 m/sec velocity, but it was not effective at more than 3 m/sec wind velocity.
Although it is a well known fact that preheating flame is very useful in the oxygen cutting of steel, there is dearth of information specifically stating the reasons for the effect of the preheating flame on the cut material. The effect of the preheating flame has been studied and several fundamental informations were obtained. Author attempts to present these informations in three reports. The purpose of this paper (Report 1) is to discuss the specific problems of the heating effect on the cut material, will the conclusion that little preheating is needed to keep the cutting reaction.
An equation has been derived for wetting equilibrium between molten alloy and solid metallic surface by taking account of terms for the potential energy of gravity and for alloying in the vicinity of interface. The equilibrium condition is given by σS=σLCOSθ+(σLS+fa)-ε where σS, σL and σLS are respectively the surface energies of the solid and the liquid phases and the interfacial energy between them, θ is the contact angle, fa the alloying energy per unit interface, and ε the energy due to gravity. It was pointed out that fa, could. have a large value compared with the interfacial energy. The value of fa was estimated for molten silver containing palladium in contact with a nickel plate, and the result was compared with experimental facts.