This paper describes a new measuring method of residual stress distributions in welds qualitatively using an optical interference method. The principle of this method is based on measuring by an interference fringe (surface relief), induced on a specimen when deformed and/or treated by stress-relief annealing. The method may be characterized mainly in the following measurements: 1) Only by lapping a surface of a specimen, the location of stress concentration and the range of plastic deformation can be easily known. 2) Combined with cutting and annealing, unique patterns of surface relief are revealed respectively due to stress release in z-, xy-, and xyz- directions. 3) This method can be also utilized under subzero temperature, and furthermore, even at higher temperature by use of a laser.
An algorithm and program for determination of welding parameters of CO2 V-butt one pass welding is studied. The proposed program is applicable to the globular transfer condition of 1.6 mm wire diameter. The Jackson's experimental relationship between groove shape and penetration depth was used to determine a penetration as a function of crosssectional area of V-groove. Calculated parameters were confirmed experimentally to give the full penetration and good bead appearance of V-butt joint from 9 to 16 mm in thickness.
Underwater circular welding of steel pipe which was set vertically was carried out in horizontal position using a water curtain type CO2/MIG arc welding method, and it was proved that this method was applicable to the underwater circular welding of pipe. (1) For 6.4 mm thick steel pipe, I groove was adopted and the appropriate welding conditions to get a full penetration of root and stable bead shape were revealed in relation to a root gap, welding current and welding speed. One pass or two pass welds was excellent in penetration and bead shape all over, and passed the tensile and bending test. (2) For 16 mm thick steel pipe, multi-layer welding was carried out with spray and short circuiting arc. So far as the appropriate welding conditions were selected, welding results were excellent both under water depth of 1 m and 50 m. Mechanical properties of welds were excellent not only in tensile and bending test but also in impact test.
Problems arising with speed up of seam welding and their countermeasures are discussed. These are summarized as follows. (1) The upper limit of welding speed is restricted by decrease of ΔIa/Iav. This limit can be raised by arranging preheating electrodes in front of welding electrodes. (2) The upper limit of welding speed for air tight welding is restricted by discontinuity of joint for plate thickness less than 0.8 mm. (3) As welding speed increases molten metal comes to solidify where electrode does not be applied resulting in occrence of internal defects. These internal defects can be prevented by arranging forging rollers at the back of welding electrodes.
With improvement of .shielding method and prevention of heat dissipation from the surface of the mother metal, the study on the possibility of underwater welding of HT50 and HT60 was undertaken. The results obtained are as follows. 1) With the use of water curtain, surrounding water did not intrude the welds and fluxtuation in welding thermal cycle curve shown in the usual underwater welding was not recongnized. 2) With improvement of shielding method under water, the cooling rate was moderated and resembled to that in the air. 3) The method covering the surface of the mother metal with tape was available for prevention of heat dissipation from the surface and moderated the cooling from the side of the bead. 4) The hardness of the weld metal and HAZ decreased with increasing of heat input and showed the qualitative correlation with the cooling rate. 5) The maximum hardness of HT50 was less than 38OHv and would not cause the actual problem.
The weldability of commercial pure titanium to 304 stainless steel by resistance spot welding was investigated by means of tensile shear test and macro- and microstructural observations. The results obtained are as follows 1) It is rarely successful to obtain reliable joint strngth by directly welded titanium to 304 stainless steel because of the formation of brittle intermetallic compounds mainly composed of TiFe2. 2) Ductile weld joints are produced by an application of the insert metal sheets of 1100 aluminum and their maximum tensile shear strength reaches about 350 kg/spot. 3) In case of the weld joints having the insert metal sheets, an intermetallic compound layer is formed between 304 stainless steel and 1100 aluminum but the ductility of the joints is not lost unless the compound layer grows and fills up the nugget in the insert metal sheets of 1100 aluminum.
Delayed crack behaviour from a notch of poor penetration, in a we ldments of HT80 steel of 31 mm thickness has been investgated. Three points bend specimens of 70 nim width with weld defect of poor penetration were welded. In these specimens, the tip of thenotch was located on a fusion line in modified-Vee joints. J integral has been applied to evaluate the delayed fracture toughness in coarse grained HAZ, Results can be summarrized as follows: 1) Fracture mode of the pressure vessel at proof loading, that is the transition from stable delayed cracking to unstable cleavage fracture, can be easily reappeared by the laboratory test proposed in this report. 2) The susceptibility to delayed cracking in the weldments of HT80 steel can be iuccessfully evaluated as a function of J integral. 3) A new method to evaluate delayed fracture toughness has been proposed. This method is based on three parameters method proposed by, S.J. Garwood et al. 4) Delayed fracture toughness's transition curve is shifted to higher temperature side than fracture toughness's transition curve by 25°C.
The growth of stress corrosion crack has been investigated for SUS 304 stainless steel in 42 % MgCl2 boling aqueous solution (143°C). Fracture mechanics was applied to the problem of crack growth, because their branching and irregurality at the crack front are relatively small. The curves which show the relation between the crack growth rate, da/dt and stress intensity factor, K were divided into two regions, region I of lower K-value and region II of higher K-value. In region I, da/dt was approximately proportional to the square of K. In region II, after discontinuous drop, da/dt increased again with increasing of stress intensity factor. It has been shown that. linear elastic fracture mechanics can be applied to SCC testing in the range of lower stress intensity factor but in the range of higher stress intesity factor the influence of crack branching has to be considered before applying fracture mechanics.