The flux action of soldering has hardly been investigated in relation to chemical reaction. This research was carried out to clarify the relation between flux action of organic acid (stearic acid) and spreading phenomenon of solder; and the reactions between stearic acid and base metal (Cu) or between the flux and solder (Sn-Pb eutectic solder) were studied. The results obtained are summarized as follows: 1) The sperad obtained on oxidized copper using stearic acid flux is greater than on electropolished specimens. 2) Stearic acid reacts with copper oxide on heating to give copper stearate, as well as clean the surface of copper plate. 3) With stearic acid flux containing a littel of copper stearate, the area of spread increases very markedly. 4) Copper stearate reacts with melted solder to give stearic acid and copper metal. From these results, the flux action of stearic acid may be considered as follows: Stearic acid reacts with copper oxide to give copper stearate, which reacts with solder and a Cu-rich layer in outer surface of solder is formed. So, the spreading of solder on copper plate becomes better.
It is well known that a small amount of ferrite in austenitic stainless steel weld metal is very effective for the prevention of hot cracking. But the reason seems to be not quite clear. This experiment was carried out to know the relation between the solidification phases, sulphur microsegregation and hot cracking susceptibility of Ni-Cr alloyed steels. Because it has been confirmed by previous experiment that γ iron crust of primary solidification phase through the peritectic reaction of Fe-Ni system is very responsible to the hot cracking of 3.5% nickel alloyed steel weld metal. Circular groove hot cracking test specimens were prepared by three series of Ni-Cr alloyed cast steels, which contain about 0.15% sulphur. The groove of specimen was welded by TIG and MIG welding. The experimental results obtained are as follows; (a) The weld metals which crystallize as primary γ iron are much more sensitive to hot cracking than those which crystallize as primary α iron and transform to γ iron. This result concides with the tendency of sulphur microsegreagation of weld metals, which was detected by EPMA. (b) The hot cracking susceptibility of Ni-Cr alloyed steel weld metals relates to the boundary line of primary γ or α solidification surfaces, while the ferrite amount of weld metal at the room tenperature by Schaeffler diagram seems to have no direct relation with the susceptibility.
A weld thermal-restraint stress and strain-cycles simulator, briefly "Thermal Restraint Simulator; Thermorestor", which enables us to simulate various phenomena caused by welding, and to analyze separately the effects of each factor such as thermal cycles, restraint stress cycles, strain cycles and atmosphere upon materials, has been developed. It is confirmed that this apparatus can be applied to making clear weld cracking phenomena, to evaluation of weldability of base metal, to selection of welding materials, to establishment of welding procedure and so on. Examples of standard programs and their application tests for investigation of welding phenomena with this apparatus are as follows: 1) The program of a rigid restraint control during synthetic weld thermal cycles can make clear the weld hot crack sensitivity in the heat-affected zone of base metals. 2) By the program of enforced strain control during synthetic weld thermal cycles they can investigate the hot crack sensitivity and the propagation characteristics of micro-cracks of base metlas or weld metals, and me program is useful for selection of base metals or welding materials. 3) The program of a constant strain control during cooling of a notched specimen charged with hydrogen at a high temperature can make cleur the phenomena of delayed cracking due to hydrogen, and is very useful for the evaluation of cold crack sensitivity during welding and dealyed cracking characteristic during operation. 4) The programs of various controlled strain or stress during weld post-heat treatment can make clear stress relaxation and anneal cracking phenomena, and are used for decision of the conditions of stress relief heat treatment and the evaluation of anneal crack sensitivity of base metals.
Spot welding condition for mild steel, as recommended by RWMA, has been applied to practical application, and as lowest as possible electrode force is utilized in any class conditions. And only in the condition of given thickness, change of current dendity in relation to weld time under any welding conditions results in the same curve and we found that nugget area should be in proportion to welding current. We have paid special attention to this relation, and studied about the selection method of spot welding conditions.