In this paper, the corrosion fatigue behaviors of as-welded specimens, welded and machined specimens under plane bending cantilever machine, and artificially notched specimens at the H. A. Z. of weld bead under rotary bending cantilever machine were investigated in the dripping of 3% salt water. Tested materials were mild steels, and welding procedures were performed by submerged arc welding. The relations between the strength reduction factor βk due to the stress concentration factors of the reinforcement or the artificial notches, the factor βc due to corrosion, and the factor βkc, that by the gathering effects of corrosion with reinforcement or artificial notches, are discussed. The following conclusions may be drawn from these test results. (1) At the 107 cycles, the corrosion fatigue strength under dripping salt water was reduced by 40-50% than in air. (2) In the plane bending, the factor βkc was nearly equal to βk×βc, but in the rotally bending, the factor βkc was smaller than βk×βc. (3) In the corrosion fatigue test, the welded metals did not form the weak zone for the initiation of cracks so far as the surfaces were smoothly machined.
An investigation was made to examine mechanical properties of welded type 304 stainless steel at elevated temperatures. The stainless steel plate 14 mm in thickness was welded with inert-gas arc-welding, without pre-heating. Three different kinds of filler metals, 3.2mm in diameter, were used and their chemical composition and the mechanical properties are shown in Table 1. Fatigue and tensile test specimens were machined from the welded joint so as to get the weld metal at mid portion of the specimens, as shown in Fig. 2. V-notch Charpy impact specimen was also made from the welded joint. A rotating beam fatigue test, running 3, 400 rpm, was carried out at 650°C, while the tensile test, hardness test and impact test were carried out at temperature ranging between 350°C and 750°C. The highest fatigue strength was observed for the specimen welded with Fox 16/13 Co metal. The specimen failed consistently at base metal and the endurance limit is about the same value as that of the base metal. The specimens welded with either NC-36L or NC-38 metal showed lower endurance limit than that of the base metal and failed always at weld metal. (See Fig. 3) The highest fatigue resistance observed in the specimen welded with Fox 16/13 Co may be attributed to the strain induced precipitation of niobium carbide at plastically strained region. This was also verified by the fact that the most remarkable coaxing effect in fatigue was observed in this specimen, as shown in Fig. 6. While the fatigue strength of the welded specimens was markedly decreased by solution heat treatment at 1100°C for 1 hr after welding, little change was observed in the fatigue strength after stress relief heat treatment at 870°C for 2 hr. (See Fig. 5) Tensile test was carried out at temperatures from 600°C to 700°C and failure of the specimens occured at or near the weld metal. The proof stress was increased by welding. The endurance limit observed at 650°C was rather higher than the proof stress measured at the same temperature. A fairly low impact value was obtained on the weld metal and also at the heat affected zone, comparing with higher toughness of the base metal. (See Fig.8) The impact value of weld metals increases with increasing test temperature up to about 600°C, while a sharp drop is observed at around 650°C in each specimen. In the specimens welded with NC-36 L or NC-38, the impact value increased rapidly with increasing temperature after reached their minimum at around 650°C. This minimum is attributed mainly to the precipitation of chromium carbide. (See Fig.9) On the other hand, NbC can precipitate fairly rapidly only at high temperature of the order of 950°C so that there is no recovery appeared in the impact value but further decrease with increasing temperature was observed in the specimen welded with Fox 16/13 Co metal. An about 5 mm wide hardened zone was observed both sides of the bead. From the result of the present investigation, it may be possible to conclude that the mechanical properties of welded portion of austenitic steel at elevated temperature is much affected by their micro-and macro-structure, especially by the carbides precipitation.
In order to apply the spot welding to primary structures, it is necessary to know not only the static and fatigue strength of welds or these consistencies but also the distortion-coefficient of spot welds and the load-share among the rows of multiple spot-welded joints etc. In the case of riveted joints, the values of coefficient and the formula of load-share have been obtained basing upon various experiments. However, in the case of spot-welded joints, the value of coefficient and its application have not yet estimated. This report deals with the distortion-coefficient of spot welds of the Al Alloy being widely used in structures of aircrafts. Moreover, it has been clarified to be able to calculate the loadshare ratio as riveted joints.
When friction welding is actually applied to parts of a machine, its mechanical strength is an important problem. Results of tensile and bending test have ever been reported, however, those of impact and fatigue test are seldom reported yet. S 20 C and S 45 C are tested on tensile, bending, fatigue and impact strength, and showed result as follows : (1)Tensile test Both as welded and normalized material after welding are broken at the points that are not welded, therefore their strength is equal to that of base metal. (2)Bending test Welded material is sometimes broken at weld interface even when welded on conditions which it stands in tensile test, however such a phenomenon will not happen when welding conditions are properly decided. (3)Fatigue test Both smooth and notched testpiece as welded, was increased fatigue strength by friction welding, and normalized testpiece after friction welding is equal to that of base metal. (4)Impact test Impact strength became much smaller by friction welding. After all, except the decrease of impact strength, the strength of friction welded carbon steel is almost equal to that of normalized carbon steel.