The importance of convective heat transfer in the weld pool has been widely recognized in relation to the penetration shapes of base metal. The main causes that associate streaming in molten pool are the electro magnetic force, buoyancy force, surface tension and aero dynamic drag force. But, the mechanism of heat transfer has not yet been clarified well. Therefore, in this work, they have paid special attension on the importance of convectional heat transfer in the weld pool and the anode size or heat source size under the same heat input, or same current value. A finite difference method was employed to solve above-mentioned mechanism. The results obwere tained as follows. 1) When arc length is short, the velocity field induced by outward surface shear strss consists of two flow loops of opposite directions in the molten pool, which lead to comparatively deep weld shape. 2) In case of short arc length and positive temperature coefficient of surface tension, surface tension is predominant. Accordingly, penetration shape is deep. 3) In case of long arc length aero dynamic drag force is predominant, which leads to the 'shallow' center and 'deep' peripheral penetration.
The feasibility of gravity welding and welding phenomena under pressurized argon atmosphere (up to 5 MPa gauge) were investigated. The ilminite type, high titanium oxide type and low hydrogen type electrodes of 4 mm in diameter were used. As base metals, SM41A steel plates of 6 and 9 mm in thickness were used. Main results obtained are summarized as follows: 1) Sound weld can be obtained under pressurized argon atmosphere up to 5 MPa by low hydrogen type electrode. Porosity and pits are not observed in the weld, but occurred by the other type in the pressure range of 0.1 to 0.7 MPa, which disappeared when pressure is over 1.0 MPa. 2) The suitable welding current to obtain sound welds increases with increasing ambient pressure. 3) Butt welded joints obtained by low hydrogen type electrodes under pressure up to 5 MPa have sufficient tensile strength and impact value. However, the tensile strength and the impact value decrease with increasing pressure. 4) The maximum voltage Vmax and the mean voltage Vmean increase with increasing pressure up to 2 MPa. However, they have a tendency to decrease over 2 MPa. The minimum voltage Vmin decreases with increasing ambient pressure. 5) The melting rate of electrode decreases with increasing pressure up to 0.5 MPa, while it increases over 0.5MPa. 6) The transfer period of droplet from electrode tip increases with increasing pressure up to 0.5 MPa, while it decreases over 0.5 MPa. 7) The diameter of droplet increases with increasing pressure up to 0.5 MPa, while it decreases over 0.5 MPa.
The increase of the weld fumes was one of the problems in arc welding under high pressure as an underwater welding. The fume generation phenomena in MIG welding under high pressure were studied and the formula to estimate the fume generation was proposed. It was shown that the fume generation was closely connected with the arc power which increased with increasing of pressure. Therefore the selection of low arc voltage and low current condition such as short circuiting arc welding was important to decrease the fume in high pressure. The welding in DCEN, especially in high current condition was also recomended because the fume was decreased with increasing of pressure and the bead shape was similar to that of DCEP in high pressure.
Welding defects such as porosity, spike and solidification crack have sometimes occurred in deep penetration electron beam welds. These defects are attributed to the complicated welding phenomena, i.e. the interaction between electron beam and metal, the molten metal flow and its solidification. In this report, the formation mechanism of a longitudinal crack and the molten metal behavior in electron beam welding have been investigated. The results obtained are as follows. (1) Longitudinal crack sensitive regions could be classified into two types according to the formation mechanism. (2) The longitudinal crack occurred in the high welding speed range was caused by the lack of molten metal at the narrow rear solidification wall. (3) In the low welding speed range, remarcable concave of solidification line in the backward direction of the welding, which means the occurrence of the local delay of the solidification, was recognized for just or upper focussing condition. The longitudinal crack was apt to occur in this delayed portion. (4) The delayed solidification was resulted from remelting or secondary melting effect of the solidified wall by the stagnated molten metal in a beam cavity.
The use of zinc-coated steel sheets in industries has increased rapidly. Spot welding of galvanized steel sheets, however, has been a problem from the beginning. That is poor electrode life due to high welding current. An attempt has been made in this program to improve weld quality deterioration in the spot welding of galvanized steel sheets. Aluminum oxide powder is interposed at the interface between two galvanized steel sheets to be welded, having an aim to increase contact resistance at faying surface. Tests have indicated that the powder addition is much effective to reduce weld time requirements and consequently, for improving tip life and welding performance.
A new pressure joining method has been developed for transition joints between aluminum and copper pipes. The joining procedure is characterized by the following steps. 1) The ends of aluminum and copper pipes are set into contact with each other under a initial pressure that does net result in plastic deformation of the pipes. 2) The pipes are rapidly heated by an induction mtehod up to a temperature just above the eutectic temperature. 3) After an adequate quantity of eutetic liquid is formed, a second pressure, which is highre than the initial pressure, is applied to exclude the eutectic liquid out of the interface. Changes in the length of aluminum and copper pipe are detected to estimate the quantity of eutectic liquid. When the length changes by a predetermined value, the heating is terminated to cool the joint and the second pressure is applied. Many pipes of diameter 8 mm were joined in a protective gas atmosphere under various condition for the amount of eutectic liquid and the second pressure. The joints were evaluated by a metallographic examination, mechanical tests and leak tests. The residual eutectic layer at the joining interface becomes thinner with increasing second pressure. Joints with a layer less than 0.1 μm in thickness were obtained at a pressure of 30 MPa. Joints with such thin layers never break down at the joining interface during repeated bending fracture tests, but the aluminum pipes break down outside the interface. The leak rate of helium in the joints with thin residual eutectic layers is less than 1×10-13Pa m3/s even after joints were subjected to repeated bendings, thermal cycles and flattening deformations.
To eliminate all voids on diffusion-welded interface, diffusion-welded joints were treated using a hot isostatic pressing equipment without the canning of joints. The material used was SUS304 stainless steel. Results obtained are summarized as follows: 1. All voids on diffusion-welded interface, that are shut from the external environment and have not residual gas, are eliminated by the hot isostatic pressing treatment. 2. In the case of the welding surface prepared by a lathe, all voids on diffusion-welded joint are shut from the external environment when welded area ratio is above 35%. 3. It is difficult to eliminate voids in diffusion-welded joint made under the welding environment of Ar. 4. All voids of diffusion-welded joints are eliminated under hot isostatic pressing conditions of 1100°C, 2h and above 50 MPa. 5. The joints subjected to hot isostaic pressing treatment after diffusion welding have very small change in specimen shape, and the mechanical properties of the joints is not influenced by the roughness of welding surface.
The solid-liquid interface phenomena in cemented tungsten carbide (WC-6% Co) /carbon steel (0.11%, 0.47%and 0.85%C) joints brazed with copper filler metal and the shear strength of the joints have been studied. In copper brazing of cemented carbide to carbon steel, the carbon steel dissolves into molten copper filler metal and, simultaneously, the dissolved iron deposits from the cemented carbide as the columnar phase at a constant brazing temperature-that is, a "dissolution and deposit of base metal" takes place. The columnar phase consists of Fe-6-11%Co-11-10%Cu-0-1%W-0.5%C alloy for the combination of 0.11%C steel; Fe-6-15%Co-9-8%Cu-0-2%W-0.5%C alloy for 0.47%C steel; Fe-7-17%Co-l0-8%Cu-0-2%W-0.9%C alloy for 0.85%C steel. The growth of the columnar phase is faster as the carbon content of the steel is smaller. In cemented carbide/0.11%C steel joint, the shear strength of the joint increases from 346 MPa to 441 MPa when both base mtels are linked with the columnar phase.
Cutting of FRP by plasma jet was studied for dismantling the used FRP boats. The plasma jet cutting conditions such as plasma gas composition, gas flow rate, current, cutting speed and so on were cleared to estimate the cutting ability of FRP. The burning of resin was prevented and the narrow and parallel kerf was achieved by the wet cutting method. The main results obtained are as follows. 1) The cutting ability was lowered with increasing of the glass content in FRP. 2) The cutting ability was affected with the gas composition and the gas flow rate. The maxìmum cutting was performed by the mixed gas of Ar+30%H2. 3) The cutting ability of FRP was lower than mild steel. 4) The recomended ratio of nozzle length and nozzle diameter was 3-4 in the plasma jet cutting compared with about 2 in the plasma arc cutting. 5) By the wet cutting method, the burning of resin was prevented and the narrow and parallel kerf was obtained. 6) The plasma cutting was able to apply to the dismantling of the used FRP boats.
It was shown that the fume generation was the problem in the plasma jet cutting of FRP in previous report. In this report, the effects of cutting conditions and the glass contents in FRP on the fume generation was studied. The fume was collected with the high volume air sampler prescribed in JIS-Z-3930. Some of the counterplans were considered for decreasing the hume. The main results obtained are as follows. 1) The fume increased in proportion to the glass content in FRP. 2) The catched fume corresponded to about 1/3 of glass content in FRP. 3) The fume generation decreased 30-50% in wet cutting condition compared with dry one. 4) The perfect catch of the fume was difficult by means of setting water under the material to be cut. 5) Almost all the fume was composed with the particles less than 0.1 micron. 6) The composition of the fume was nearly same as the glass composition and it was composed with amorphous materials.
The purpose of this paper is to investigate the effect of coating configuration and heat treatment on the thermal shock resistant properties of the ceramic plasma sprayed coatings including the graded coatings. The results obtained are summarized as follows: 1) The press sintered heat treatment induced a higher adhesion and cohesion strength between the substrate and Ni-based alloy by means of diffusion. However, similar results were not obesrved at the alloyalumina interface. 2) The graded coating configuration, which consist of an alloy undercoat, an alumina overcoat and an intermediate graded layer, revealed superior thermal shock resistant properties. This was attributed to their better ability to relax the thermal stresses developed between the Ni-alloy and alumina layers.
The dissolution phenomenon of the base metal into the liquid insert metal during the transient liquid insert metal diffusion bonding (TLIM bonding) of Ni base superalloy MM-007 was investigated. The influence of the oxide film on the dissolution phenomenon of the base metal into the liquid insert metal was also investigated. Main experimental results obtained in this research are as follows; (1) The dissolution of the base metal into the liquid insert metal occurred preferentially at dendrite boundary. (2) The dissolution phenomenon of the base metal into the liquid insert metal can be described by Nernst-Brunner's theory. (3) In the early stage of dissolution process, dendrite boundaries in oxidized base metal were preferentially dissolved and subsequently dissolved zones linked each other. (4) In the dissolution process, oxide film was seperated from the base metal and subsequently moved toward the center of the bonded interlayer. (5) The dissolution process of oxidized base metal was divided into three stage according to the dissolution rate constant K. In the Stage I, K value is smaller than that of the base metal without oxidation. In the Stage III, K value is same as that of the base metal without oxidation. Stage II is the transient stage on K value. The change of K value is due to the behavior of oxide film. Namely, in Stage I, the oxide film is stable and prevents direct condact of the liquid insert metal to base metal. However, in Stage II, the oxide film is torn and the liquid insert metal conducts to the base metal without any interruption. (6) In the Stage I, the dissolution rate was reduced as thickness of the oxide film increased. The decrease in the dissolution rate is due to the decrease in the diffusion flux of B into the liquid mating base metal through the oxide film with the increase in the thickness.
For evaluation of crack susceptibility of medium, high carbon low alloy steels to quenching crack type cold cracking in HAZ during welding, the effects of hardness and chemical compositions on fracture stress during cooling have been studied by the simulated cold cracking test using commercial and laboratorial nineteen kinds of steels. The fracture stress showed a good correlation with the fraction of intergranular fracture surface. Therefore, it was understood that the fracture stress is useful to evaluate crack susceptibility of quenching crack type cold cracking. The fracture stress had a tendency to decrease with an increase in hardness. With respect to intergranular fracture, it is considered that the steels showing the hardness higher than about Hv600 are susceptible to quenching crack type cold cracking. Moreover, phosphorus is very harmful because it lowers the fracture stress due to increasing intergranular fracture surface considerably. Furthermore, the regression analyses on the fracture stress in relation to hardness and such impurity contents as P, N, Sn and O showed; (i) the fracture stress mainly depends on hardness and P content, (ii) N is harmful, too, but the effect is much less than P, (iii) Sn and O has little effect.
Carbide precipitation in niclel based alloy takes place at elevated temperature. The tendency of this phenomenon is stronger than in austenitic stainless steel. But the carbide precipitation in HAZ of nickel based alloy has not been investigated enough as that of austenitic stainless steel. The effect of weld thermal cycle on carbide precipiration of 15Cr-75Ni alloy (UNS N06600) and its relation with intergranular corrosion in nitric acid were investigated. And prevention of sensitization in HAZ was investigated from the view point of chemical composition. The susceptibility to intergarnular corrosion in HAZ agreed with the carbide behavior during weld thermal cycle and aging so far as the aging heat treatment condition of this work. The carbide in the base metal overaged is solid soluted and nucleates at the grain boundary by weld thermal cycle, and the carbide precipitated and grew during aging. The chrominm depleted zone has not healed after aged for 15 hours at 823K, so the carbide caused the intergranular sensitization. The sensitization in HAZ of 15Cr-75Ni Alloy can be prevented by the suitable addition of Nb; Nb/ C<40 in weight ratio.
From practical standpoints, it is very important to set up the evaluation procedures of fracture toughness of heterogeneous materials such as welded joints. In this paper, the finite element analyses of the J-integral extended to the problem of a crack in heterogeneous materials were carried out on the compact tension type welded joints in order to examine and clarify the unsymmetric deformation characteristics of welded joints, the fracture path of them in mixed mode conditions and the relation between J-integral and total/local crack tip opening displacement. Through calculation results, the validity of crack tip characterising role of J-integral was proved. Moreover, it was confirmed that the J-integral correlated to the total crack tip opening displacement.
The present report is intended to evaluate the difference of initial fatigue crack propagation rate between mild steel and high tensile strength steel in notch field subjected to high stress. Two used materials (SS41, HT80) have similar characteristics in long crack propagation (R=-1) when small scale yield condition is satisfied. However, in low cycle (high stress) region (R=-1), initial fatigue crack propagation rate in center notched strip of SS41 is higher than that of HT80. This characteristics might result from elasto-plastic effect on fatigue crack propagation. By application of ΔJ calculated in this study, the asto-plastic effect could be evaluated. As the results, it would be mentioned that initial fatigue crack propagation rate in notch field behaving elasto-plastically can be estimated from master curve of long crack by ΔJ considering cyclic yield strength of materials.
The present report is intended to evaluate the effect of residual stress on initial fatigue crack propagation rate in a notch field. Initial fatigue crack propagation rate in tensile residual stress field of center notched stip (SS41) is affected by both of residual stress and elasto-plastic behavior. In low cycle (high stress) region, the effect of elasto-plastic behavior is remarkable. But in high cycle (low stress) region, the effect of residual stress is conspicuous. The relaxation of residual stress by yielding of notch field was modeled and confirmed by experiments. ΔJ to initial fatigue crack in notch field was calculated by considering the model on the relaxation of residual stress. As the results, initial fatigue crack propagation behavior in notch field with tensile residual stress could be interpreted by using the ΔJ.
The countermeasure for improvement of the bend ductility of the low interstitial ferritic stainless steel overlay welds has been investigated. The addition of stabilizing elements, especially zirconium, up to about 0.4% to the first layer of the ferritic stainless steel overlay welds with 30% chromium on a low alloy steel improved its bend ductility. The bend ductility of the overlay welds was also improved with decreasing the chromium content in the first layer of the weld metal. On the basis of these results, a composition of 19Cr-2Mo-0.25Zr-Fe was recommended for the filler metal for the first layer of the 30Cr-2Mo steel overlay welding on a low alloy steel in order to ensure a good weld ductility.
The mechanism of improvement of the bend ductility of the low interstitial ferritic stainless steel overlay welds prepared with zirconium containing low chromium type steel filler metal for the first layer has been investigated. In the previous report, it was indicated that the thickness of chromium carbide, 475°C embrittlement and grain coarsening were factors affecting embrittlement in the overlay welds. Decreasing in chromium content in the first layer of the weld metal contributed to mitigation of 475°C embrittlement and decreasing of the thickness of chromium carbide on the grain boundary in the overlay weld metal. Addition of zirconium to the first layer of the ferritic stainless steel overlay welds made the thickness of chromium carbide decrease and also the grain size refine. These resulted in an excellent weld ductility for the overlay welds.
Experimental evaluation of hermeticity and joining strength and an investigation of joints by SEM, EPMA, AES, were accomplished on hermetically sealed package by Micro-Parallel Seam Joining (MPSJ) using a lid (Fe-Ni-Co alloy) normally applied as hermetic seal of ceramic package for highly reliable LSI, nickel plated in both Watts Bath and Sulfamate Bath. The results are summarized as follows. (1) Crack was observed at the grain boundary in a plating layer at the joining interface of ceramic package which was hermetically sealed with use of nickle plated lid in a Sulfamate Bath. The crack is considered to be caused by sulfur segregation at the grain boundary from the result of investigation by SEM and AES. As a result, both hermeticity and joining strength were unsatisfactory. (2) Tendency of crack occurrence was observed to be especially notable at the seam joint after thermal cycling test performed to evaluate reliability of joint rather than immediately after joining. Therefore, thermal cycling test is considered to be an effective means for evaluation of crack occurrence. (3) Crack was not observed at the joining interface of hermetically sealed package using nickel plated lid in a Watts Bath and indicated to be a sound joint structure. Both hermeticity and joining strength were resulted to be satisfactory. However, peeling of plated layer at an area of the lid slightly away from the joining section was observed on a lid applied with thick plating of 10μm. Therefore, plating thickness of approximately 3.5μm in a Watts Bath is considered to be adequate. (4) Correlation between hermeticity and peel strength was not found on package hermetically sealed with use of nickel plated lid in a Sulfamate Bath. Although specified value for hermeticity was satisfied, peel strength was zero or a value close to zero on some specimens. Therefore, both methods are required to be performed as an evaluation method for joint of hermetically sealed package by MPSJ method.