The purpose of this study is to improve solderability of stainless steel with various kinds of electro plating such as Sn, Cu, Ni, Ag, and Au of thickness from 0.5μ to 10μ. At first we have tried to investigate the solderability of plated or not plated stainless steel sheet with special designed speading machine. Next we have carried out peel test of soldered joint which seems to be most suitable method to examine the mechanical property of soldered joint. Results of our investigation are summerised as follows: 1) Among various electroplating of stainless steel, Sn plating shows best spreading. 2) It was found in the peel test that the kind of plating and the soldering temperature affects the peel strength. It decreases in the following turn in terms of plating metals Cu, Ni, Ag, So, and Au from 48 kg/cm in case of Cu to 12 kg/cm in case of Au. 3) In So plating, bright plating contributes to the peel strength by 20% lower than dull plating. 4) In Ag pating the peel strength decreases with the soldering temperature. In Au plating it is affected by the degree of diffusion between Au and Sn-Pb solder. The more the diffusion proceeds the greater the strength is. 5) The platingthickness does not affect much the peel strength in such kind of metal as Cu and Ni with little solubility. On the other hand in such metals as Ag and Au with rapid diffusion in solder, it has an remarkable influence. 6) Concluding from fracture study by micro-scopic and E.P.M.A. examination, it could be made clear that the peel strength lowers when the plated layer disappears during soldering process.
It is proved that the keyhole type plasma arc welding method is very effective to the high speed circumferential joint weld of centrifugal cast steel pipe HK-40. In such a case, however, the proper programming is necessary as to the start of weld, formation of back bead, crater treatment, etc. Such an optimum programming is obtained.
In previous papers, we have shown that welding residual stresses distributions and welding deformations were determined by thermo-elasto-plastic parameters. But the effect of transformation expansion on residual stresses and welding deformations is not clear. In the present paper, we deal with the effect of transformation expansion on residual stress distributions and welding defomrations. Main conclutions obtained are as follows: (1) Transformation expansion has effects upon residual stresses distributions, but does not have effects upon welding deformations. (2) Differences of welding deformations between mild steel and high strength steels depend on their yield strength. (3) Preheat temperature influence considerably residual stresses distributions of high strength steels, when yield strength σY is greater than or equal to 0.252 (θr-θi-θav). (4) Conventional formulae are presented for calculating residual stresses distributions and welding deformations of high strength steels.
Studying on the abnormal structure (Ni rich zone) formed near the gas cutting edge by acetylene gas cutting, the change of its compositions and oxidation weight increment were measured using 5.5% Ni steel and 9% Ni steel. The results are summarized as follows; (1) The width in Ni rich zone by acetylene gas cutting tends to increase with an increase in the supply of oxygen. On the other hand, Ni rich zone was scarcely measured near plasma cutting edge. (2) Judging from the results of X-ray analysis, FeO and Fe3O4 were mainly observed in oxide by gas cutting, but Fe-Ni solid solution besides them were contained in the oxidation film by oxidation experiment. In Ni rich zone, Fe-Ni solid solution was only observed. (3) Activation energy calculated from weight increment by oxidation experiment was 33-38 kcal/mole for Fe and Fe-(1-3%) Ni alloys, and 54-61 kcal/mole for 5.5% Ni steel and 9% Ni steel. Activation energies calculated from weight increment and thickness in Ni rich zone were nearly equal, but differed from that calculated from thickness in oxidation film in 9% Ni steel. From the above result, the rate process of oxidation in Fe-Ni alloys may be considered as the forming process of Ni rich zone. (4) Oxidation weight and oxidation thickness can be drawn as a function of Lalson-Miller's parameter, P=T(log t+C). Those linear lines deflected on the point of T(log t+10)×10-3≈12.5.
Acoustic emission technique which has been used as a research tool to the deformation and fracture of materials or as a method of non-destructive inspection is tried to apply for detection of the delayed cracks in weldments. The acoustic emission measurements are carried out right after completion of slag removing to avoid the noise from the welding arc and the slag cracks. No special problems due to interference from the transmitted mechanical noise or the electrical circumstances can be encountered and the acoustic emission data recorded in terms of count rate by an electric counter are attributed to the burst type emission from weld cracking. Experiments reveal that the initiation and growth of delayed cracks in HT 80 weldments can be readily detected and discontinuous process of slow crack-growth can be characterized by means of this new system used. In y-groove restraint cracking test using MIG, the effect of various factors in practice, such as restraint intensity, preheating temperature and weld heat input, on the primary and secondary incubation periods of delayed cracking can be evaluated in details and accurately from the acoustic emission data. Both preheating and postheating treatment retard effectively the initiation and propagation of cracks, and these phenomena are well reflected upon the acoustic emission count. The acoustic emission technique is concluded to be useful to detect weld defects and to understand a mechanism of the hydrogen cracking.
Grain-boundary migration on the weld interface is one of the most important factors affecting the solid phase weld properties. In this report, the behaviour of grain-boundaries in the vicinity of the weld interface during solid phase welding is pursued continuously with a high temperature microscope, and a observation method to oxidize a specimen slightly at a high temperature is compared with thermal etching method. The main results obtained in this observation are as follows; 1) In case of observing grain-boundary migration with thermal etching, a sufficient understanding of the nature of thermal etching is indispensable. High temperature oxidizing method is suitable to know the location of grain-boundaries at arbitary time. 2) Grain-boundary migration near the solid phase weld interface is restricted in various way by the interface. For instance, the grain-boundary that coincides with the weld interface is very hard to migrate to leave from the interface compared with the other case. In the vicinity of the weld interface, such grains as have very unstable shapes transiently are often observed; etc. 3) Various processes of grain-boundary migration starting from a grain-boundary triple point formed on the weld interface are observed. (Fig. 3) At the interface without a grain-boundary triple point, the bulge type grain-boundary migration is observed.
It is generally acknowledged that the ductile welded joint of copper to aluminum is difficult to be made by fusion welding because of forming intermetallic compounds. This paper gives the result of research in the application of diffusion welding for joining copper to aluminum, and describes about the influences of basic welding process parameters, such as pressure, temperature and time, upon the weldability and intermetallic compounds. Besides the application of the insert metal (only pure metal) is studied. The following results were obtained. 1. The diffusion welded joint of copper to aluminum without the insergt metal is sound under the proper welding condition, and this joint strength is coincident with one of similar aluminum. But intermetallic compounds, such as Al2Cu and Al4Cu9, form along the welding interface at higher temperature and in longer time than the proper welding condition. The joint strength decreases, when the thickness of intermetallic compounds increases more than about 10μ. The relation between welding time (t sec) and temperature (T°K) free from embritttling due to intermetallic compounds is t <8×10-5 exp (25000/RT). 2. In diffusion welding with the insert metal, it is difficult to find out insert metals which accomplish the sound welded joint without embrittling entirely. But silver is suitable as the insert metal that restrain the embrittling of welded joint. And the range of the proper welding process parameteres becomes broader with suitable thickness of the insert metal. 3. It is effective, according to circumstances, to utilize the eutectic reaction between the insert metal and base metal. Silver and zinc are suitable for this purpose, but welding process parameters must be carefully controlled to supress intermetallic compounds.