In the weld metal, generally, subgrains are developed inside of columnar crystals or equiaxed dendrites and solutes segregate along boundaries of the subgrains. Accordingly, the content of the solutes dissolved in the weld metal would change when the subgrains are developed in the weld metal. The change of magnesium content dissolved in the weld metal of aluminum-magnesium alloy was investigated with X-ray diffraction technique. The main conclusions obtained are as follows; (1) Magnesium content dissolved in the weld metal decreased gradually as the growth proceeded from the fusion boundary to the weld center. (2) When the weld heat input increased the magnesium content dissolved in the weld metal decreased. (3) The magnesium segregated along boundaries of the subgrains. (4) After heat treating the weld metal for 24 hr at 550°C the magnesium which had been segregated along boundaries of the subgrains dissolved again in aluminum matrix and the magnesium content dissolved in the weld metal became almost the same as one in the base metal.
By use of basic physical quantities from the practical standpoint, a trial has been made in formulating relationships in viscosity-diffusivity and viscosity-surface tension of molten metals at or near the melting point. Using the expressions, which have been drived by authors from the theoretical standpoint, the relationships in viscosity (ηm), diffusivity (Dm), and surface tension (γm) of molten metals at or near the melting point can be expressed with such basic physical quantities as atomic weight (M), melting point (Tm) and atomic volume(Vm) as follows: Dm=3.5×10-6(Tm/M)1/2Vm1/3(From the modified Stokes-Einstein.) rm/ηm=7.0×103(Tm/M)1/2 rmDm=1.4×10-5Tm3/2/Vm1/3M1/2andrm/ηmDm=2.0×109Vm-1/3 ≈ 109
Strange silver white spots appeared in fracture sufrace of tensile test specimen of C.E.S. weld metal and hydrogen charged weld metal. We studied on this phenomenon s are the results obtained are as follows. (1) Those silver white spots are micro weld cracking and fish eye. (2) Micro weld cracking includes small columnar structure and fish eye do not include columnar structure. (3) Micro weld cracking is similar to so called "Ice flower structure. (4) Weld cracking in the C.E.S. weldment has been considered as a hot crack, but that is a cold cracking induced by hydrogen.
Sulphides formed in TIG-arc weld metals of Fe-S-Mn ternary alloys and the solidification, crack susceptibility have been investigated. At the same time the applicability of the law of coincidence for change in liquid compositions during non-equilibrium solidification has been examined. Main conclusions obtained are as follows: 1) The shape and structure of sulphides and the crack susceptibility of weld metal can be classified by Mn3/S ratio which was expected by the law of coincidence. 2) In the weld metal whose Mn3/S is less than about 0.83, sulphide is composed of FeS and (Mn, Fe)S. Its shape is filmlike at the columnar grain boundary and globular at the cell or cellular dendrite boundary. Moreover solidification crack always occurs along the filmilike sulphide. 3) In the weld metal whose Mn3/S is bteween 0.83 and about 3, only (Mn, Fe)S is generally formed, whose shape at the columnar grain boundary is still filmlike. Solidification crack also occurs along the filmlike sulphide in high welding speed. 4) In the weld metal whose Mn3/S is more than about 3, obvious eutectic composed of iron and small (Mn, Fe)S of granular shape is formed at both the columnar grain boundary and the cell or cellular dendrite boundary. In this weld metal solidification crack does not occur.
The studies in this report were carried out to clarify the effect of Mg on the hot ductility of 75 Ni-15 Cr-Fe alloy and to investigate the relation between the existence of Ni2Mg and (Ni2Mg+Ni) and HAZ cracking. The results are summarized below: 1. Increasing content of Mg, hot ductility of 75 Ni-15 Cr-Fe alloy becomes worse and grain boundary breaking occures remarkably. 2. The existence of Ni2Mg and (Ni2Mg+Ni) is thought to be the cause of HAZ cracking in 75 Ni-15 Cr-Fe alloy. 3. HAZ cracking of 75 Ni-15 Cr-Fe alloy can be prevented by means of solid solution treatment for Mg.
In order to prevent the cracking in the weldments under the humid atmosphere some considerations on the adequate control of welding material and on the welding process are conducted. H-type restraint cracking tests are carried out under the various intensities of restraint and diffusible hydrogen contents. The results are summarized as follows; (1) It is found clearly that MIG welding is the most suitable process in the humid atmosphere because of its low mixing ratio of the air into the arc atmosphere. (2) Absorption characteristics of the electrode coating mainly depend on the absorption to the binder and that to the capillary tubes with various radii, and the moisture content in the coating υ is given by υ=υe(1-e-α't) where υe is an equilibrium moisture content, α' is a constant depending on the surface construction and t is an absorbent time. (3) The water vapor is perfectly dissociated in the arc column, and then it acts on the diffusible hydrogen in the weld metal as the same manner as hydrogen in the arc column. (4) The diffusible hydrogen content in weld metal will more contribute to the crack sensitivity of HT-80 weldments than the intensity of restraint. (5) Root cracks observed in HT-80 weldments initiate either at the unmixed or transition zone in the neighborhood of weld bond. Therefore, it can be estimated that the chemical composition of weld metal also affects the crack sensitivity.
The experiment on galvanized steel plate was carried out by manual welding with various types of electrodes and automatic gas-shielded metal-arc welding. The experimental results were as follows: 1) Good-appearance beads and sound welded joints were obtained by ilmenite, lime-titania and high titanium oxide type electrodes. Appearances of beads by high cellulose and low hydrogen type electrodes were good, but blowholes or slag inclusion in weld metals were observed by the X-ray. On the other hand, good appearances and sound welded joints were obtained by CO2, CO2-O2, Ar-CO2 or Ar-O2 shielded-gas metal-arc welding. 2) Sound welded joints were satisfactory in tensile strength and ductility in comparison with the base metals. Zinc content of weld metal showed no detrimental effect on its mechanical properties. 3) Zinc content of weld metal was the highest by low hydrogen type electrode (0.054%) and it was the lowest by high cellulose type electrode (0.025%). On the other hand, zinc content of weld metal was the highest by CO2-O2 shielding gas (0.037% and 0.044% ) and the lowest by Ar-O2 shielding gas (0.010% and 0.024%) in the case of high current, high voltage condition and short circuit transfer condition, respectively. 4) Amount of fume of the galvanized steel plate about 2 times as much as that of the not galvanized steel plate in the case of coated electrodes and it was several times with gas-shielded metal-arc welding, especially it was the highest by CO2-O2 shielding gas. And so, it seems that the arc welding of galvanized steel plate has no special difficulty with the precaution of ventilation.
Experiments were conducted to study the structural features of weld-solidified metal in commercial 5083 aluminum alloy and its influence on the fracture behaviors. The shape of weld bead was considerably influenced by welding variables and heat input. In these behaviors, height of reinforcement was influenced by the heat input but depth of penetration was done mainly by the welding current, while width of bead depended on the both of them. Structures of common 5083 alloy welds containing no refining elements consisted of fine columnar, coarse columnar, granular and feather grains. In these structures, the volume fractions of fine columnar and feather grains were increased with heat input but those of coarse columnar and granular grains were decreased reversely. The width of columnar grain had a tendency to increase with heat input. On the other hand, 5083 alloy welds containing small amounts of Ti-B showed the fine granular structure all over the fusion zone. When weld metals having fine columnar, coarse columnar and granular grains were stretched, crack occurred preferentially at the grain boundary of coarse columnar structure. In weld metals having taining feather grains, however, it was important to consider the relationship between the growth direction of feather grain and the stretching direction. Crack occurred preferentially at feather grain when stretched transversely to growth direction of feather grain but it did not occur in this way when stretched parallelly.
Effect of welding current and sampling method on the nitrogen content of weld metals in nitrogen and air atmospheres using a pure iron electrode wire was studied. Three methods i.e. depositing on a mild steel plate, rotating copper disk and water cooled copper block were used for sampling at different current levels. The main results obtained are summarized as follows; 1. The nitrogen content of weld metals obtained by the bead on mild steel plate method decreases slightly in a nitrogen atmosphere but largely in an air atmosphere with increasing welding current. 2. The rotating copper disk method is not suitable for the study of nitrogen absorption as the weld metal droplets are not so rapidly chilled in water bath and the arc condition is pretty different from that of the conventional arc welding. 3. The water cooled copper block method is more suitable than the rotating copper disk method for studying nitrogen absorption through arc space, though it can not be used at the ionhigher currents. 4. The head on plate method is useful for studying the absorption of nitrogen by molten droplets and weld pool at low welding current.