It was shown in previous report that the maximum intensity of propane-oxygen flame was given by a stoichiometrical gas mixture for complete combustion and also that the time to start melting a steel plate was shorter at the inside of the inner cone of flame than at any other part of flame. Therefore in this paper, it is investigated if such a propane-oxygen flame, by which the shortest time to start melting steel plate is obtained, is available for welding. And aluminum-containing welding rods are used for bead-on-plate test of rimmed or killed steel plate under various flame conditions. Morover, porosity and mechanical properties of some butt-welded joints by aluminum-containing rods are examined. The results obtained are summarized as follows : 1) The ratio of Si/Mn is also important to prevent porosity of weld metal, i.e. a too high content of silicon is detrimental to the prevention of porosity. 2) Aluminum in welding rod ranging from 0.20 to 0.35% is more effective for prevention of porosity than silicon and manganese, and such an aluminum content of rod gives good mechanical properties of welded joints. 3) Outside of inner cone of the flame the ratio of oxygen/propane less than 3.2 is most suitable for welding.
The contact angle of molten silver on Fe-Mo and Fe-W alloys with various compositions was measured at 1100°C. Measurements were also made on the contact angle of Ag-25% Pb alloy on the (100) surface of a Fe single crystal at 850°C. The results of measurements on the wetting of Fe-Mo and Fe-W alloys showed that no appreciable difference existed between the contact angle on the a iron phase and that on the γ iron phase. This may be interpreted as caused by a sturctural irregularity at the interface, since Ag is considered a γ stabilizer in iron alloy. The contact angle of Ag-25% Pb alloy on the Fe single crystal was not different from that on the polycrystalline surface.
In the foregoing reports, comparison in creep rupture strength between large and small size welded specimens, discussion on the mechanism of creep rupture and the influence of heat treatment after welding were made. In this report, the difference in rupture configuration between large and small size welded specimens, and welding methods viewed from creep rupture configuration are discussed. The large size welded specimens are ruptured at the heataffected zone of base metal (HAZ) near the bond, while the small size welded specimens are ruptured at HAZ near the base metal. The plate thickness of the steel used is 30 mm, and the welded joints are made by multi-layer welding. Therefore, it may be considered that the properties at welded joint of specimens of both sizes are different. It is clear from the foregoing report that creep strength may be proportionate to the absorbed energy to rupture in a high temperature tensile test. Therefore, tensile tests at 450°C on synthetic HAZ specimens, with respect to the coarse grain part near bond and the fine grain part near base metal in HAZ of small size welded specimens, are carried out to measure the absorbed energy. The value of absorbed energy in fine grain part is less than that in coarse grain part. Consequently, it may be considered that small size welded specimens are ruptured at fine grain part of HAZ near base metal, while large size welded specimens are ruptured at coarse grain part of HAZ near bond. The creep rupture configurations of large size specimens are discussed in various ways. As a result, it is believed to be desirable for improving the creep rupture strength of welded joint to make the pentration of the final bead as shallow as possible.
Weld cracking susceptibility, or simply, weldability, is a most significant problem in utilizing high strength steels. A new formula, based on the result of restraint weld cracking test, is herein proposed for the calculation of the cracking parameter Pc: Pc=C, %+Si, %/30+Mn, %/20+Cu, %/20+Ni, %/60+Cr, %/20+Mo, %/15+V, %/10+5B, %+t, mm/600+H, cc/100g/60 (t: plate thickness, H: diffusible hydrogen in weld metal) Cracking parameters calculated from this formula have a good correlatioh with the test data obtained from the y-groove restraint carcking tests using 200 types of high strength steel. The carbon equivalents adopted in JIS and the result of weld carcking tests correspondingly indicate that the steel with higher carbon equivalent is more susceptible to weld cracking. However, data are scattered so widely that the carbon equivalents cannot be applied for estimating weld cracking susceptibilities of high strength steels. Since the carbon equivalent specified in JIS does not include the terms of diffusible hydrogen and plate thickness, even the steels with the same carbon equivalents reveal a higher cracking susceptibility when their diffusible hydrogen content or plate thickness value increases. Comparing with some typical carbon equivalents, which have been suggested so far, Pc's present the best agreement in predicting the weld cracking susceptibilities. Although there is a weak trend that the higher the maximum hardness in HAZ, the higher the weld carcking susceptibility is, the maximum hardness does not represent strictly the weld cracking susceptibility. The relationship is investigated between cracking parameters, Pc's, and the preheating temperature to prevent weld cracking and the following equation is obtained. T(°C)=1440 Pc-392
There are many factors lowering the fatigue strength of welded joints, for example, undercutting, geometrical effect of reinforcement, residual stresses, microstructural change in weld heat affected zone, etc. Among those many factors, we tried to study the fatigue strength of weld heat affeeted zone of various kinds of high tensile strength steels, including ultimate strengths from 60 Kg/mm2 to 80 Kg/mm2. In order to reproduce the microstructures of various portions in weld heat affected zone, test pieces were subjected to thermal cycles by the synthetic thermal cycle aparatus, with the peak heating temperatures of these thermal cycles set at 640, 740, 850 1000 and 1350°C; then machined to V-grooved specimens. Amsler's high frequency vibrophore fatigue testing machine was used. Fatigue limits of all notched specimens as well as those of smooth specimens subjected to weld thermal cycles are nearly equal to or higher than that of each base metal and are proportional to static tensile strengths of various portions in weld heat affected zone. These results mean that the reduction of fatigue limits of butt weld joints of high tensile strength steels including ultimate strengths from 60 Kg/mm2 to 80 Kg/mm2 is not due to the micro-structural change in weld heat affected zone. Difference in fatigue behavior between different steels, is explained by the previous lath structure of low carbon martensite.
Effects produced on propane-oxgen cutting by the kinds and coating thicknesses of primary anticorrosive paint were examined. The anti-corrosive paints were classified roughly into four kinds: long-exposure type wash primer, Non-Zn epoxy primer, orgnic Zn-rich primer, and inorganic Zn-rich primer. The results aobtined are as follows. 1. The coating thicknesses were examined using a microscope and a coating thickness meter. When the coating thickness was small, both values agreed with the actual coated thickness. But when the coating thickness was larger, the coating thickness meter indicated a smaller measured value than the actual coated thickness. 2. With non-coated materials, proper conditions for S-1 (devergent type) and C-2 (straight type) cutting tip were examined. The proper conditon for S-1 cutting tip was 6 kg/cm2 of oxgen pressure and 70 cm/min of cutting speed, and that for C-2 cutting tip was 4kg/cm2 of oxgen pressure and 80 cm/min of cutting speed. 3. With a coated steel plate, the cutting speed was examined by varying the kinds of anti-corrosive paint, and the coating thicknesses. In Zn-rich coating materials, a reduction in the cutting speed was clearly observed and this tendency became more pronouned with the increase of the coating thickness. 4. Regarding the S-1 cutting tip and C-2 cutting tip both used in the cutting test, the gas flow and the expenses involved were calculated for comparison. As the result, the S-1 cutting tip was found more advantageous in terms of laboratory experiments.