In the lay down welding, we carried out the fundametal experiments on the influences of kind of covering, covering composition, eccentricity ratio, arc current, groove angle of bese metal and welding position, causing to the penetration depth. Furthermore, it became clear that the widest coexistence area of the good penetration area and the good bead area as per Report No. 2 at flat and horizontal fillet weldings, is the electrode whose covering composition is in case of acidic type-Iron prowder 30%, Gas generating material 20% in case of basic type-Iron prowder 20%, Gas generating material 30%.
Fatigue tests on plates with transverse fillet welded attachments were performed to confirm the fatigue strength of fillet welds joining the web plate and stiffener of a box girder of a bridge fabricated of 80 kg/mm2 high strength steel. Pulsating tension fatigue tests have revealed the following facts: (1) In the present test range of leg length (h) (h=8-20mm, h/T=0.34-0.82, T being the thickness of main plate), the fatigue strength of plates with transverse fillet welded attachments, is little affected by the leg length of fillet. Even beyond the present test range of leg length the effect of leg length will not be great. The 2×106 cycles fatigue strength of plates with transverse fillet welded attachment, if statistically treated assuming it to be independent of the leg length, will be 13.2 kg/mm2 (in terms of joint factor, βj=3.33) and 11.6kg/mm2 with non-failure probability of respectively 50% and 90%. (2) As a method for improving the fatigue strength of plates with transverse fillet welded attachments, machine-finishing of the toe of fillet weld has proved effective. Though the effect was minor for a notch radius at the toe of fillet weld p=2 mm R, the improvement amounted to 5-6 kg/mm2 in fatigue strength and 3-6 times in fatigue life, at p=5 mm R. (3) The critical fillet size (hcr) in a fillet welded tee-joint has been found to be 1.8<2hcr/T< 1.9; and thereby the 2×106 cycles fatigue strength (plate stress) of it is estimated at about 10.4 kg/mm2, which is lower than the fatigue strength of plates with transverse fillet welded attachments.
In this report, authors have discussed the effect of the chemical displacement reaction between metal chloride added to ZnC12 flux and Sn-Pb solder on the spreadability of the solder. The spreadability of solder is measured by spread area of the solder for sessile drop method. The chemical displacement reaction between solder and flux is examined by X-ray diffraction of the solder, and by value of free energy of formation of metal chloride (ΔG°Mcln). When ΔG°MCIn of metal chloride added to ZnCl2 is greater than ΔG°snCl2 or ΔG°pbCl2, the remarkable chemical displacement reaction between solder and the added metal chloride may take place and it may lead to a increase in spread area of the solder (BiC3, SbC13, AgCl, NiC12⋅6H2O). Nevertheless, when ΔG°MCIn of added metal chloride is pretty small than ΔG°SnCl2 or ΔG°pbC12, the chemical displacement reaction does not almost take place and the spread area of solder is similar to the spread area with pure ZnC12 flux (CdC12.51/ZH2O, LiCI, KC1, NaCI, CrC13⋅6H2O). Though ΔG°MCin of added metal chloride is smaller than ΔG°snC12 or Δ°Gpbc12, when remarkable difference between ΔG°MCIn and ΔG°snC12 or ΔG°pbCl is not recognized, the chemical displacement reaction takes place and the spread area of solder may change (FeCl2⋅nH2O).
Causes and mechanisms of the cracking in HT 100 weldments are investigated by use of three kinds of test method. Both the hot and cold cracking are not observed in the heat-affected-zone, but mainly observed in the weld metal. From metallographic examinations conducted on these fractured specimens, it can be found that the hot cracking is located in cellular dendrite boundaries, where solutes, such as Ni, Mn, and Mo, are segregated. Even when none of hot cracking is observed, the special etchant with a surface active agent reveals darken-broading cellular dendrite boundaries in the weld metal that are sustained plastic deformation during solidifing. The plastic deformation generated during the cooling process has also a deleterious effect to the delayed cracking. It is found that under the presence of hydrogen, the weld metal cracking initiated at abovementioned cellular dendrite boundaries transfers to the austenite grainboundaries, and then into the grains. In paticular, these cracks tend to occur at the place where the cellular dendrite boundary coincides with the austenite grainboundary. It is estimated to be due to the solute segrigation, dislocation pile-up and the precipitation of carbide.
In previous paper, it was presumed that the most important factor to cause the grain-boundary liquation in the heat-affected zone of test high strength steel (HY-type, HT100) was the low-melting point eutectic reaction between Cr and Ni elements which had been swept up and enriched to grain boundary. In this paper, the further investigation on the grain-boundary liquation was conducted, especially to obtain a certain understanding of the effects of sulfides on it, using a free cutting steel. As a result of this study, it became to be decisive that the sulfides, such as MnS, were secondary and not important factor of the grain-boundary liquation in HAZ of HY-type high strength steel (HT100), and that the primary factor of it was the most likely to be the eutectic reaction between Cr and Ni swept up and enriched to grain boundary.
Up to this time, the authors studied the weld cracking phenomena in typical and fundamental cast Ni-base superalloy, Inconel 713C, to get information on the weld cracking phenomena of cast Ni-base superalloys. It is the purpose of this study to clarify the main cause of weld cracks in cast Ni-base superalloy, B-1900 which has more excellent mechanical properties than those of Inconel 713C, according to the information about hot cracking phenomena in Inconel 713C. From experimental results, it was made clear that weld cracks in B-1900 were hot cracks and the main cause of hot cracks was low melting point-fine white constituents crystallized at grain boundaries.