This report deals with the strength of partial penetration groove welded joint which has become a subject of general interest in architecture but of which little information is available. In this report it is found that the theoretical evaluation of the strength based on the theory of localized necking agrees with the experimental results. In the series of experiments the results obtained are as follows. 1) The yield strength and the maximum strength of throat area increase with an increase of the depth of penetration (p) and decrease with an increase of the leg length (f) (cf. Fig. 8, 12, 14, 20). 2) The maximum laod of the welded joint increases with an increase of the depth of penetration (p) and the leg length (f) (cf. Fig. 9, 13, 15 21). 3) The fracture mode is affected with a ratio of p/f. When p/f is smaller than 1.5, the fracture arises in the fillet weld metal, and when p/f is larger than 1.5, the fracture arises between the base matel and the heat affected zone. (cf. Photo. 1, 2, 3, 5). 4) In the usual design of the joint, the theoretical equation (2) or Fig. 4 is well applicable.
According to the researches already carried out, it is clear that brazed joint strength of specimen with coarse brazing surface is greater than that of ones with smooth brazing surface. It is considered that these phenomena depends on the effect of the following factors: 1) Actual contact area of brazed joint. 2) Residual stress of brazed joint. 3) Hardness distribution of brazed joint. This paper presents some experimental evidence of residual stress measured by X-ray stress maesuring process and hardness distribution measured by micro-Vickers hardness tester. To obtain smoe experimental data, 10 × 32 × 2.6/m/m mild steel as the base metal and BAg-8 as a filler metal were prepared, and the abutting surfaces of base metals were Polished with various emery papers (No. 60, 120, 240, 400, 600mesh) to set up various roughnesses on the brazing surface. These specimens were brazed with BAg-8 filler metal in the 35 kW resistance furnace operated in hydrogen atmosphere. Residual stress measuremtnt was carried out by means of an X-ray Rstess measurement diffractometer manufactured by Tokyo Shibaura Electric Co. These examinations gave the results as follows: 1) Residual stress of brazed joint with coarse surface was larger than that of ones with smooth brazing surface. 2) Eesidual stress of y directio n (Fig. 7, 8) was larger than that of x direction; it is considered that these phenomena were caused by soliditic shrinkage of filler metal at the brazed joint. 3) Most of these residual stresses were tension stresses, their max value being 4.5kg/mm2 and their min, value being 0.1kg/mm2.
It has widely been accepted that the hydrogen which diffuses from weld metal into base metal in the arc welding plays an important role in embrittlement and formation of delayed cracks in the heat affected zone of weldment, but the direct measurement of such hydrogen has scarecely been reported. This paper describes a new device has been used to determine the volume of hydrogen diffusing from weld metal into base metal as a function of time, and the effects of moisture in the coating of electrode, strength of steel and preheating temperature on the behavior of hydrogen diffusing into the heat affected zone are investigated. The mian results obtained are as follows; 1) By the use of a vacuum system, the technique can accurately estimate the hydrogen diffusing from weld metal into base metal for a comparatively simple device. 2) When electrode containing the same humidity is used, the hydrogen content in the heat affected zone of weldment decreases with increasing strength of steel. 3) The hydrogen content in the heat affected zone increases with the increase in preheating temperature, and the magnitude of increment decreases as steel increases its strength. 4) It is necessary to consider the chemical composition of base metal in the hydrogen test of weld metal, because about half of the diffusible hydrogen estimated by JIS method may be the hydrogen diffusing into base metal. 5) The behavior of hydrogen in the heat affected zone of weldment during and after the arc welding may be dealt with engineering parameter D proposed in this paper on an assumption of unidimensional diffusion of hydrogen.
It is well known that a low melting point filmy sulfide causes hot cracking in a steel weld metal. Especially, in the case of nickel steel weld metal containing over 2.5% of nickel, the occurrence of such hot cracking becomes more significant even in a small amount of sulphur, such as 0.01 %. In this paper, the effect of alloying elements, which can effectively change the iron sulfide film into other sulfides of higher melting point and of globular form, was studied to prevent such not cracking. The experimental result showed that hot cracking of 3.5% Ni steel weld metal can be prevented by addition of strong sulfide forming elements, like zirconium or titanium. These elements are much more effective to prevent such hot cracking than manganese. Sulfide inclusion of these elements seems to be globular type of MnS, TiS or ZrS, respectively.
The transverse cracking in the submerged arc weld metal of HT-80 steels in heavy sections has become the object of increasing attention in the last few years. In order to make clear the relation between the transverse crack and the diffusible hydrogen in weld metals, a window type restraint weld cracking test and a restraint fillet weld cracking test have been performed in this investigation. It is shown that the combination of the highly basic agglomerated flux which generates plenty of CO2 gas in welding and the wire which contains an adequate amount of alloying elements produces transverse crack-free weld metals. The main results obtained are summarized as follows; 1) The transverse crack observed in the multi-layer butt weld metal is formed in the region of the fusion line of final layer. 2) The diffusible hydrogen has a close relationship to the generation of transverse cracking. In addition, the interaction of oxygen and sulpher with hydrogen at the austenite grain boundaries has to be considered in regard to the cracking. 3) In the horizontal fillet weld joint, two kinds of transverse cracks are observed. One is a crack at the weld root and the other is a crack in the weld metal. 4) The transverse cracks generated in the multi-layer butt weld metal and the horizontal fillet weld metal are of the same kind. These cracks propagate along the austenite grain boundary. 5) The longitudinal crack observed in the horizontal fillet weld metal is a kind of hydrogen-induced crack which starts at the weld root. In the case of the weld metal with a low hydrogen content, this kind of cracks can be prevented by preheating or postheating, or otherwise by decreasing the strength of the weld metal.