In the previous report, it was pointed out that martensite-like structure formed at weld bond of welded α-steels and γ-steels reduced the ductility of weld bond remarkably. The substance of martensite-like structure has not been cleared, because the structure is very fine. In this report, the substance of the structure was cleared up by transmission electron microscopic observation. The effect of C content in α-steels on the amount of above mentioned martensite-like structure was also investigated. Moreover, investigations were made on the hardness change of the structure with post-weld heat treatment and so on. Martensite-like structure is not formed uniformly along the whole weld bond, but formed mainly at a stagnation area where flow of the molten metal contacting with the fusion line does not occur. Martensite-like structure was identified as a mixed structure of low carbon martensite or bainite (in case of using low carbon α-steels as base metal), or high carbon martnesite or bainite (in case of using high carbon α-steels as base metal) and fine chromium carbide (Cr23C6). The amount of martensite-like structure formed at weld bond increases with increasing C content in a-steels, but it decreases with too much C. In the post-weld heat treatment at 650°C, the weld bond is softened with increasing heating time, but bigin to be hardened when heating time is over app. 2 h and hardened remarkably over app. 7 h. This hardening is caused by large amounts of Cr23C6 precipitates which are induced by the carburization from haz of α-steel. On the microscopic observation of weld bond, the hardly etched region was observed between the martensite-like structure and weld metal. This region is very hard and hardened further with post-weld heat treatment. However, the substance of the structure of this region could not be cleared up.
Inside of columnar crystals which are developed in the weld metal of commercially pure aluminum subgrains are generally observed. Besides, Al-Fe compound is developed along boundaries of the subgrains. These subgrains would affect the mechanical properties and corrosion resistivity of the weld metal. In this report the investigation was made on the change of weld solidification structure when the weld metal was annealed at high temperature which had been as-welded, tensile strained or cold rolled. Macrostructures after annealing were grouped into following three classes: (i) macrostructure similar to that as-welded, (ii) base metal recrystallises and in the weld metal recrystallisation occurs partially only near the fusion boundary, (iii) recrystallisation occurs all over the weld metal. On the other hand, no considerable change was observed in features of the subgrains in the weld metal. That is, it would be concluded that the subgrains are considerably stable thermally. In the columnar crystal zone of aluminum weld metal fiber texture is developed whose fiber axis is . This fiber texture was also observed after the annealing in the area where the columnar crystals were observed in the weld metal, but disappeared in the area where recrystallization occurred. Then, the intensity distributions of FeKa radiation in the weld metal were measured with electron probe microanalyser. Each maximum in the intensity distribution curves corresponded to the part which was observed black in the microstructure. Electron micrographs showed that in the weld metal which was annealed at high temperature there existed both compounds and dislocations along the boundaries of the subgrains. This phenomenon is similar to that which was observed in the as-welded metal. When the weld metals which had been tensile strained or cold rolled were annealed the boundaries of the subgrains became discrete and rod- or granular-shaped compounds were also observed inside of the subgrains. These compounds found to be A13Fe by selected area diffraction.
A method obtaining transient distributions of two energy densities in the hole drilled by high energy density beams such as laser and electron beams was proposed: wv which passed through the plane perpendicular to the beam axis and ws which was absorbed by the side wall of the hole. In the hole of acrylic resin drilled by CW CO2 laser beam, maximum value of wv reached 2-3 times that of the focal point of the lens system used due to a "wall-focusing effect". In the hole drilled by the electron beam, the wall-focusing effect was not recognized except for near surface, and beam was rather scattered by the vapor. As the result, the CO2 laser beam produced slender cylindrical hole and the electron beam produced fat hole. The method proposed here may be applied to measure the beam power.
This report presents the structural variations such as width of recrystallized zone and recrystallized grain size of heat-affected-zone of commercially pure aluminum welds and their influences on the tensile strength. Test pannels were made by MIG welding process using 6 mm thick plate whose mechanical properties had been controlled by H1n or H2n-tempering. Softening behavior at heat-affected-zone is occurred in accordance with ordinary recrystallization sequence, but the extraordinary grain growth are not observed. The width of recrystallized zone is increased with increase of cold rolling reduction (for H1n series) and drop of pre-annealing temperature (for H2n series) of base metal, while its grain size becomes finner reversely. Softening curve obtained by hardness distribution at heat-affected-zone and peak temperature in weld heat cycle depends on only tempering conditions of base metals. The recrystallizing temperature shown in this curve is recognized to decrease with increase of cold rolling reduction or drop of pre-annealing temperature of base metal. The tensile strength of heat-affected-zone is under the severe influence of tempering conditions of base metal, that is, it is increased with increase of cold rolling reduction or drop of pre-annealing temperature. This fact seems to result from mainly the variation of grain size at heat affected zone mentioned above. So long as the base metals possess similar strength in spite of difference in tempering conditions of them, there is observed little difference in the strength of heat-affected-zone. However, width and grain size of recrystallized zone are fairly influenced by tempering conditions.
Effects of carbon and nickel on the shape of sulphide and the microsegregation of sulphur in TIG-arc weld metals of Fe-S-C and Fe-S-Ni alloys have been investigated. In these alloys the sulphur contents were purposefully made much higher than those encountered in commercial steels. For the evaluation of the microsegregation the amount of sulphides was measured with the point counting method. Main conclusions obtained are as follows: 1) Dihedral angle of sulphide somewhat increases as carbon content increases. On the other hand an increase in nickel content slightly decreases it. 2) Microsegregation of sulphur during weld solidification increases as carbon or nickel content increases. 3) Nickelsulphide was not detected in weld metal containing up to about 11% nickel.
Mechanical properties of steels and welding rods are usually random variables, so mechanical properties of welded joints which are made using those materials are also them. In this report, it is pointed out that the reliability of welded joints on static tensile strength must be considered in discussion about matching between base metal and weld metal. The average tensile strength σWu of weld metal is dependent upon the reliability of welded joints, the form of frequency histogram of their strength and the parameter r which decides the lowest required strength of weld metal. A few calculations about the average tensile strength σWu of weld metal were done and the effects of the reliability, r-value and frequency distributions on strength were considered. On these calculation results, the problem of matching was discussed in relation to the reliability.
For the purpose of decreasing the radio interference to which superimposed higher frequencies give rise, we steadied the arc by a method of substituting a discharge of condensers for the oscillation of higher frequencies after starting of the arc. This study was carried out to observe reigniting phenomena of the arc, to discuss about the most suitable pulse shape and the maximum irreducible energy required for reignition, when the base metal was aluminum.