Using Titania type electrodes that are liable to develop fisheyes in the deposit metal, depending upon the test method adopted, two kinds of specimens were prepared : one as weld and the other subjected to a hydrogen-removing treatment (250°C, 8h). They were put to a fatigue test on the Ono's Repeated Bending Fatigue Testing Machine, with the following results : 1) In the former specimen, fatigue cracks originate from micro-blowholes lying somewhat deep under the surface; while in the latter, they do so from micro-blowholes very close to the surface. These micro-blowholes correspond to the nuclei of fisheyes appearing in tension test pieces. 2) In the former, nominal stress, namely, fatigue limit with no consideration made for the locations of these micro-blowholes, is about 2-3kg/mm2 lower than in the latter (Fig.3). When, however, the crack-developing stress is considered, the difference well be about 10kg/mm2 (Fig. 5) ; this is presumably due to the variance of hydrogen content between the two.
The purpose of this investigation was to study the characteristics of spot weld in alminum alloys 24S-T when used for three phase frequency converter type spot welding system. We studied the spot weld results in shear strength, indentation, cross section and X-ray photograph by changing welding conditions of three phase spot welding. Results obtained are as follows ; (1) Indentation are generally very small because of shortness of heat cycle in comparing with single phase spot welding. (2) The influence of welding current, heating time, weld pressure on spot weld are very large. (3) The influence of forging time delay is very important to the occuring of effects when post heat current is comparably large and its time is short.
Following the previous report, in which the effects of various factors on the cooling rate at the bond of a quasi-stationary long bead were studied experimentally, additional measurements of thermal cycles in various welds were performed in the presentreport. The cooling curves at the bond of various bead welds in non-stationary conditions, namely in the crater of a long bead, a tack fillet weld, an arc strike and etc., were studied experimentally. Moreover the weld hardening charcteristics as well as the related microstructures of three structural steels were investigated by obtaining the relationship between the cooling rate at 540°C and the maximum hardness in the heat affected zone. The microstructure and hardness distribution in an arc striked portion of a high tensile steel plate was found to be quite different from those for a long bead weld.
In this paper an attempt is made to examine the physical meaning of the ultimate point always taken into consideration in the mechanical tension test of materials, on the view-point of the flow pattern appeared in excessively cold-worked mild steel. The synthesis is made under the following topics : 1. The forward necking in a tension test. 2. The flow pattern connected with the forward necking. 3. The flow pattern and the change of strain hardening rate in a torsion test. 4. The ultimate point and initiation of cracks. 5. Some features of the flow pattern : (a) the role of the grain boundary and pearlite in the flow pattern ; (b) the observation of slip bands concerned with the flow pattern.
In this report the structural interpretations are given for the torsional creep charactors, especially the transition phenomenon of the increasing creep rate with the augment of prestrain, of prestrained heat resisting steels to various extent in tension at room temperature. They are as follow : 1. Cells were observed more easily on the prestrained steels above the transition range. The structure was not prominent and not numerous of the transition range, and it was numerous but not prominent at heavy increasing of prestrain above the transition. range. 2. Considering the creep caused by the formation of cell, the transition phenomenon can be interpreted by the results mentioned above. And the approximately constant creep rate ofter the transition seems to be the sequence of the cancel of the effects of the movement of more numerous dislocations, which is deduced by the increasing of the number of cell, and of the insufficient movement of dislocations to cellboundary, which is deduced by the obscure of the structure. 3. It can be comprehended by the difference of easiness on the formation of cell at two temperature groups that the equation, γ=k(p)n p=τ, e-Q/RT where K and n are the constants, y is the creep rate, y is the shear stress, T is the absolute temperatute, Q is the activation energy and R is the gas constant, is satisfied separately within the two groups of [300°C] and [450°and 600°C]. The difficult formation of cell at latter temperature group is related with the comparative increasing of visible slip band and grain-boundary displacements for total creep strain. 4. The tendency to the reproduction of extinguished striation or, at least, the arrest of the extinguishment was observed from the X-ray diffraction photographs of prestrained steels to the transition range. It confirms the comparative easiness of the formation of cells. The striations, however, were not observed at heavy increasing of prestrain obove the transition range because the size of cell was small and the recovery was not sufficient. 5. The formation of cells is associated with the undulation observed on the surface of prestrained specimen and the easiness of the formation of cells in the prestrained steels above the ultimate-point-strain is deduced from the prominent undulation in thos steels. 6. Recrystallization did not seem to play an important role in the charactors of this experiment.
In this paper we studied on the distortion of tee-fillet welded joint under external constraint. We considered two types of constraint such as shown in Fig. 1. Deflection of mother plate is approximately represented by eq. (1) (for Case 1) or eq. (7) (for Case 2), where δ0 is angular change at the center of weld line and rectangular co-ordinates are taken as shown in Fig. 2 or Fig. 8. δ0 is smaller than the angular change in free joint, δj, as shown in Fig. 3. (c. f. specimen No. 1 and No. 7). Relation between δ0 and δj is obtained by energy method, and it is given by eq. (5), where C is a constant depending on the conditions of external constraint. (see eq. (6) for Case 1 and eq. (9) for Case 2.) Various experimental results were plotted for the coefficient of constraint C. (see Fig. 9 and Table 2). From the results of Report 2 and 6, we can obtain the distortion of tee-fillet welded joint for the given welding conditions and external constraint.
The authors measured the transformation temperatures of some high tensile structral steels under the thermal cycle similar to that of the H.A.Z. of welded plate, using a high sensitive rapid-action dilatometer and tried to find out the correlations among the hardenabilities obtained from I.LW. maximum hardness test and Jominy test and the crack sensitivity obtained from C.T.S. test. The results are as follows : 1. Hydrogen considerably drops the end of transformation temperature down below that of virgin steel, and the increasing of the content decreases the end of transformation temperature. 2. The end of transformation temperature decrease with the increase of Dearden and O'Neill's Ceq., and the smaller the cooling rate, the larger the rate of the decrase of the end of transformation temperature. Adopting the critical temperature of under bead crack determined by cottrell, we can obtain the critical Ceq. for under bead crack which may become the smaller with increasing hydrogen content. 3. Hardness is not increased so much by adding hydrogen. 4. Jominy's hardnesses show higher values then thase of the dilatometric specimens, under the same cooling rates with Jominy test. 5. The crack sensitivity of H.A.Z. increases with The increase of the diffusible hydrogen of electrode and Ceq. of materials. This is to be construed as the decreasing of the end of transformation temperature with the increasing of hydrogen content and Ceq.. The increase of Ceq. drops the critical cooling rate for under bead crack, and the Si-Mn type steels seems to be inferior to vanity type steels.