Weihave studied the welding conditions which made the pear-shaped bead and also learned the relations between the coefficients of bead shape (P/W, Wm/W and A/P) and it's crack in the former reports. In this report, we studied the heat flow to welding divaction and the solidification pattern in the foundry model similar to the pear-shaped bead. At first, we investigated the heat flow in the welding bead changing it's speed and conducted that at the welding speed over a certain limit, the heat flow could be considered as 2-dimentional flow on a plane perpendicular to the welding line. Next, we made foundry models similar to the pear-shaped bead and studied the solidification pattern in it. From these results, we conjectured the location and the cause of the pear-shaped bead crack.
Various mechanical methods of improving the fatigue strength were investigated by using the base metal and cruciform fillet welded joint specimens fabricated from 40kg/mm2-80kg/mm2 steels, and the results were summarized as follows. The fatigue strength of cruciform fillet welded joints fabricated from various steels were almost the same, and their 2×106 cycles pulsating tension fatigue strength were 11.3-12.4 kg/mm2. In comparison of the 2×106 cycles pulsating tension fatigue strength of 80 kg/mm2 steel cruciform fillet welded joints, the toe ground one was 1.5 times, the peened one was 2.06 times, and the toe ground and peened one was 2.58 times (both effects of grinding and peening were found to be nearly added) as many as as welded one. The effect of improving the fatigue strength is considered to originate chiefly from the compressive residual stress induced by peening. These methods of improving the fatigue strength were more effective in alternating tension and compression than in pulsating tension. Also, in 40 kg/mm2 steel cruciform fillet welded joint, the peening treatment was effective to some extent.
In copper brazing to iron and molybdenum or tungsten, iron base metal dissolves into molten copper filler metal and the plate-like deposit of the iron develops from molybdenum or tungsten base metal to iron one at a constant brazing temperature. Simultaneously, the diffusion layer consisting of intermetallic compound Fe7Mo6 or Fe7W6 also develops into molybdenum or tungsten base metal and may deteriorate the mechanical properties of the joint.
Authors reported already that a precoat-heated stainless steel plate with mixed salt fluexs which were made by adding NiCl2 or FeCl3 to KCl-LiCl system eutectic salt showed a good property for spreading of BAg-5 using KCI-LiCl system eutectic salt flux. In this paper, after a stainless steel plate pre-coated with the mixed salt fluxes which were made by adding CuCl or CoCl2 to KCI-LiCl system eutectic salt flux was heated, corrosion products formed on the plate surface were analyzed by SEM and X-ray diffractometer. On the other hand, spreading tests with KCl-LiCl eutectic salt flux were carried out to know the effect of corrosion products for spreading of BAg-5 on the precoat-heated plates. Moreover, to clarify the flux action of used eutectic salt, the extents of spread area obtained on several pure metals which have the same property as corrosion products were considered by thermochemical calculations based on the reducing reaction heat of each pure metal oxide. The results are summarized as follows; 1) The spreading of BAg-5 on the precoat-heated stainless steel plate increased similarly to that of the case of previous NiCl2 or FeCl3. In the CuCl mixed salt flux, the increasing of spreading depended on the increasing of plate surface area due to Cu particles precipitated on the original stainless steel surface. On the other hand, in the CoCl2 mixed salt flux, the precipitated Co particles alloyed rapidly with Fe of the stainless steel plate compositions and converted into Co-Fe alloy layer. This phenomenon was the same as that in the FeCl3 mixed salt flux. Accordingly, the improved spread area in this case may be attributed to the formation of this alloy layer, namely, "De-chromiumnization" phenomenon on the surface of stainless steel plate. 2) The spreading of BAg-5 using KCl-LiCl system eutectic salt flux on the pure metals such as Cu, Co, Ni and Fe base plates depended on the reducing power of used flux for the formed oxide film on the base plate and was not affected by the wetting force of both each base plate and BAg-5.
It has been already found out experimentally that all what to be done in order to prevent the occurrence of the transverse cracks which occur in the thick weldments by the submerged arc welding process is to decrease hydrogen concentration in the welded zone and that, to do so, a low temperature postweld heat treatment was a very effective method. Then, as the first step for clarifying the concrete conditions of the low temperature postweld heat treatment to prevent the occurrence of the cracks, in this paper the correlation between the hydrogen concentration in the welded region just after welding and the practical welding conditions, such as preheat and interpass temperatures, welding speed, plate thickness, and dimensions of a welded structure, is investigated by using an analytical computer program employing the finite element method which can estimate the hydrogen distributions presented in the previous paper. First, we introduce a parameter τ of the hydrogen diffusion during welding, of which values can be determined both by the welding thermal history and by the temperature dependence of the hydrogen diffusivity coefficients, and clarify the correlation between its parameter and the hydrogen concentration just after welding. Next, considering the compensatory heating by gas burners during welding, we find out the relationship between its parameter and the welding conditions.
In this study, the influence of segregation behavior of P on the crack openning displacement (Φc) and intergranular fracture ratio at 600°C in T-1 type HT80 steels was investigated to make clear the reheat cracking phenomena in these steels. From the results obtained in this study, it was elucidated that P atoms segregated to grain boundaries of these steels during heating up to stress relief temperatures and as the results, intergranular fractures caused by the decreasing of cohesive strength of grain boundaries occurred more easily at 600°C in these steels.
The influences of various heat cycles and postheating conditions on the notch ductility of simulated heat-affected zones were studied using a heat cycle simulating equipment concerning the Cr-Mo-V cast steel. The results of these test are summarized as follows. (1) According to SH-CCT diagram of the test steel in the case of a maximum heating temperature being 1, 200°C, critical cooling time from the Ass point to 500°C for the starting point of bainite transformation is 10s. (2) In the case of cooling time from the Acs point to 500°C being 14s (15% bainite) for the V-notch Charpy impact value and 31s (70% bainite) for the U-notch impact value, the highest impact values were obtained. However, when the cooling time exceeded those values the impact value decreases with the increasing the cooling time, and the cooling time was taken to be 114s (100% bainite) then impact values remarkably decrease for both V-notch and U-notch specimens. (3) When postheated at 700-750°C, the impact value increases for each cooling curve of heat cycle. However, the influence of cooling time of heat cycle which have direct effects upon the extent of bainite transformation on the impact value does not disappear.