Occurrence of undercutting in welded joint is inevitable in some welding position such as horizontal, verticul or overhead. Undercutting, must affect the fatigue strength of welded joint as it constitutes a notch. From this standpoint, the relation between the undercut depth and the fatigue strength was experimentally studied on the test pieces, which were taken from butt welded joints and fillet welded plates of mild steel. Test pieces were prepared according to Fig. 2 in the shape as shown by Fig. 1 ; types and undercut depths of test pieces are listed in Table 2. The undercut depth was measured using the instrument shown in Fig. 3. Fatigue tests were conducted under pulsating tension. The testing machine was a 20t capacity hydraulic type. The tests were carried out up to 5 × 106 cycles. Understandably, the failure originated at the root of undercut in all test pieces. The results of fatigue tests are shown in Figs. 5 and 6, and the 2 × 106 fatigue strength value (range of stress), obtained through interpolation and extrapolation, were plotted on a probability paper (Figs. 7 and 8). Then the mean value and the values of 5% probability and 95% probability of failure were plotted against the undercut depth in Figs. 9 and 10. Considerable variances are observed in the S-N curves of Figs. 5 and 6. These variances are represented by the fattened portions of vertical lines in Figs. 9 and 10; they are particularly wide in the case of the butt welded joint with a 0 mm undercut depth, and in that of -the fillet welded plate with a 0.5 mm undercut depth. Perhaps it so seems on account of the number of test pieces being limited. As seen from Fig. 9, the fatigue strength decreases in butt welded joints with an increase in the undercut depth ; namely, it is seriously influenced by the undercut depth. By contrast, it is some what less influenced in the case of fillet welded plate, but ceases to decline beyond 0.3 mm. Perhaps there exists already a stress concentration at the toe of fillet and the notch effect in this area must be mitigated. It is due to an imperfect machining that no improvement on fatigue strength was observed in the machined test piece with a 0.46 mm undercut.
In ordinary manual arc welding, the weld metals was obtained by successive addition of graphite from lime-fluorides type flux. The effect of carbon on Charpy V-noth properties was determined on the weld metals thus obtained. Carbon fines ferrite grain size of weld metals, reduces maximum energy rapidly, increases transition temperature at a rate of 15°C per 0.1%, and widens transition range regularly.
Correlation between weld HAZ ductility and hardness were conducted for twelve high strength steels by means of a Kommerell bead-bend test. The critical values of HAZ hardness at which HAZ ductility becomes unsatisfactory were determined for each steel. These values differ not a little from steel to steel, and were concluded to be very important as a criterion of survice performance of high strength steel weldments. Furthermore, these critical values were found to be closely related to those obtained from "the synthetic HAZ ductility test" newly introduced by authors.
Authors surveyed the influences of three different methods (JIS, modified ISO and ISO) for the tensile test of deposited metal-in the former two, in as welded condition and in the latter, after hydrogen removing treatment, the test is carried out-upon fisheye appearances and mechanical properties of deposited metals from various types of mild steel electrodes, and further investigated some metal-lurgical properties of deposited metals. From the experimental results, authors found that fisheye appearances revealed in ordinary strain rate at room temperature are influenced by the deoxidation degree, the diffussible hydrogen content existing in time of test, the size and number of porosities in deposited metal.
In this report optimum spot welding conditions, mechanical and corrosive properties of welded joints for pure Zirconium (Zr) and Zircaloy-2 (Zr-2) were investigated and the following conclusions were obtained : (1) It is recommended to pickle (HF 5%+HNO3 45%+H2O 50%) the specimen prior to spot welding. (2) Optimum spot welding conditions for various thicknesses of specimens are given approximately by the following equations Welding current=5, 000+5, 000T0 (A) Electrode force=80+220T0 (kg) Weld time=1+5T0 (cycle) where T0 : Thickness of specimen in mm (3) No welding defect in nugget such as crack or porosity was detected (4) Welded joints made by optimumwelding conditions had the following mechanical properties : (i) Fracture by tension-shear test occured at the bond of base metal and heat affected zone and showed button-like fracture. (ii) The thicker the thickness, the stronger the strength by tension-shear test. The joint of Zr-2 was generally stronger than Zr. (iii) Nugget of a spot weld was harder than weld metal of a TIG weld, because cooling rate in the former was faster than the latter. (iv) Nugget showed many dendrites in macrostructure and α' (acicular α) phase in microstructure in each dendrite. (5) The holding time at temperatures over 400 or 500°C of specimen surface which contacted with air was less than 10 cycles and, accordingly, the deleterious reaction air seems to be negligible. (6) Corrosion resistance of spot weld in high temperature high pressure (320°C, 115-117 atm) test was good whether pickled or not pickled after welding. Therefore, the corrosion resistance of spot weld in considered to be satisfactory even if used in a nuclear reactor.
The crack sensitivity and the strength at high temperature of type 347 Cr-Ni austenitic weld metal with 3.5-8.5% Mn made by Argon-arc or coated metal arc welding, are researched. The ex-perimental results are as follows. (1) Addition of Mn to type 347 weld metal decreases crack sensitivity. (2) In the case of fully austenitic weld metal made by the suitable addition of Mn, Sigma phase can not be formed under high temperature for 1, 000 hours. (3) The creep rupture strength at 650°C of fully austenitic weld metal with suitable additional Mn, is superior to the standard type 347 weld metal.