Liquid phase diffusion welding of aluminium was studies. In this study, the surface of aluminium was cleaned by Ar ion beam bombardment and an alloyed film (Al-5wt.% Si-5wt.% Cu) was deposited on the bonding surface by sputtering. In this report, the effect of Ar ion bombardment on the oxide film of the bonding and weldability were investigated. The results indicated that: (1) Oxygen content on the bonding surface could be reduced by Ar ion bombardment, but the oxide film could not be removed perfectly. Wettability and weldability could be improved by Ar ion bombardment. (2) Upon heating, the alloyed film started to melt at 523°C. (3) Mechanical properties of diffusion welded joints equal to those of the base metal were obtained by the following condition: A welding temperature above 580°C, a pressure of 2 MPa and a welding time of lh. (4) Weld deformation was 1.68% with a welding temperature of 580°C and 3.28% with 610°C. Therefore, it was possible to make precise welding because weld deformation was less than that of conventional diffusion welding.
Liquid phase diffusion welding using Ni-4B alloy thin film as an insert material was investigated in order to obtain precise and high quality joints of very thin sheets. In this study the sheets of Ni, Ni-Fe alloy and Fe-Ni-Cr alloy(SUS304) were used. The thin film was deposited on the specimen (sheet) by magnetron-sputtering after cleaning the specimen surface by bombardment of Ar atom beam. Diffusion phenomena between each base metal and the thin film, and the tensile strength of joints at various thin film thicknesses were investigated. The results were as follows; (1) The melting temperature of Ni-B alloy thin film on the specimen changes by diffusion of boron atoms in heating process. Especially that of the film on Fe-Ni-Cr alloy into which boron atoms remarkably diffuse increases by more than 130°C at heating rate of 10°C per minutes and the thin film thickness of 7μm. (2) Chromium atoms have a great influence on diffusion of boron atoms in an alloy of Fe-Ni-Cr group, and then boron atoms mainly diffuse through grain boundaries. (3) Boron atoms activate the grain boundaries of Ni and quicken the movement of grain boundaries and the growth of grains. Ni-B alloy thin film of 1.4μm thickness has a greater effect on quickening them for Ni sheet of 50μm thickness than that of 7μm thickness. (4) The joint of Ni sheets welded with Ni-B alloy thin film has been almost the same as the base metal in points of the tensile strength and the metallograph at the welding conditions of welding temperature: 1100°C, holding time: 10 minutes, pressure: 9.8×10/Pa and atmosphere: vacuum.
Laser heating was applied for the desensitization heat-treatment of the surface layer in the sensitized HAZ of Type 304 stainless steel. The degree of sensitization was examined by EPR technique and the 10% oxalic acid electrolytic etch test. The CO2 laser with maximum power of 1.5kW was used for heat-treatment. Time-Temperature-Desensitization diagram (TTDS diagram) for sensitized Type 304 stainless steels were developed by calculation assuming the chromium diffusion control for desensitization which might occur when the chromium depleted zone was healed up due to dissolution of chromium carbide and chromium diffusion from the matrix being heated at the solution annealing temperatures. TTDS diagrams calculated agree fairly well with ones determined by corrosion tests. Laser irradiation conditions (e.g., Laser power, beam diameter and traveling velocity )required for desensitization of sensitized Type 304 stainless steels were calculated using additivity rule from the TTDS diagram calculated and theoretical thermal curve of laser heating derived from the heat conduction theory. After laser beam irradiated under an optimum condition predicted by calculation, the sensitized HAZ of Type 304 stainless steel restored complete resistance to intergranular corrosion.
The probability of surface hardening by means of Plasma-Ion Nitriding (PIN) process was investigated for pure Ni and commercially used Ni alloys under the condition of nitriding temperature from 773 to 1073K and nitriding time up to 32.4ks in N2+H2 atmosphere of 800Pa. Remarkable surface hardening more than Hv500 was observed for Inconel 600, 625 and 713C and Udimet 500, which were contained Cr element, and Hastelloy B, which was contAlned Mo, at nitriding temperature 773-1073K. On the contrary, Permalloy, which was contAlned Fe, was slightly hardened, and pure Ni and Monel were not hardened. From the result of X-ray diffraction analysis, CrN for Inconel 600, 625 and 713C and Udimet 500, MoN and Mo2N for Hastelloy B were detected as nitrides together with diffraction peaks from the matrix of nitrided layer and base metal beneath it. Diffraction peaks of these nitrides and matrix of nitrided layer were very broad and the half value width of these peaks had a good relationship with surface hardness, which was linearly increased as the increase of the half value width. Therefore, it was considered that hardness increased by PIN process was due to lattice expansion caused by the precipitation of such nitrides in nitrided layer.
Contact-bars of electromagnetic switchgears are required high precision and high quality at bonds. For the purpose, Vapor Shielded Pressure Bonding process and its in-process control system are successfully developed To control the material deformation, characteristics by resistance heating while bonding are examined, and the optimum electrode materials and their constitution are selected for the joint couple of Ag-Cu in diskshape as described in the report-1 and report-2. In this study, resistance heating is tried to bond the contact-bar which consists of Ag contact (φ4×t2mm) and carrier bar of 2.5%Fe-Cu material(w5×127×t0.7mm), and bonding quality is mainly examined. Then, it is clarified that the newly developed vapor shield process can be effectively applied to secure the high quality bonds. The results obtained are as follows; 1)Electrode constitution accomplished in former report can be applied to bond contact-bars. 2)Samples bonded in air atmosphere are fractured at bonding interface by peel test because of their lower bonding quality. 3)Micro inclusion is observed at the bonding interface. 4)It is clarified by EPMA inspection that the micro inclusion is FeO. 5)Torn samples bonded under vapor shield show Ag fractured mode stably because of improved high quality bonds.
Contact-bars of electromagnetic switchgears are required high precision and high quality at bonds. For the purposes, the Vapor Shielded Pressure Bonding (V.S.P.B) process and its inprocess control system are successfully developed. To control the material deformation, thermo-characteristics by resistance heating while bonding are examined, and the optimum electrode materials and their constitution are selected as described in the report-1 and -2 Then, the examination of bonding quality and its improvement by vapor shield process are described in the report-3. In this study, the mechanism of vapor shielding on cleaning action at the bonding interface and the fundamental properties of bonds are investigated. Moreover, the basic constitution of Vapor Shielded Pressure Bonding Process are examined and the each optimum condition is clarified. The main results obtained are as follows; 1) The follow facts about surface oxidation of materials are clarified by AES. a) Material heating in air atmosphere accelerates the striking oxidation. b) Vapor shield can effectively control the oxidation while heating. 2) The essential factors of vapor shield process and the typical features of bonds are clarified. a) Liquid composed by 15%-ethanol solution in water is good for vapor shield. b) Compounds both at bonds and expelled metal obtained under vapor shield are of eutectic of Ag and Cu. c) Vapor shield can raise the bond strength of 28% comparing with the one in air atmosphere. 3) V.S.P.B process for high precision and high quality of bonds consists of the suitable vapor shielding condition and the optimum resistance heating conditions
Underwater welding by gravity pulsed arc welding process and welding phenomena were investigated by using coated electrodes of three types. Main results obtained are summarized as follows: (1) When cycle time tps is approximately equal to duration of metal droplet transfer in steady current and average current Iav equal to steady welding current Id, one pulse-one droplet transfer and stable arc can be obtained. (2) In case peak time tp is equal to base time tb, when Ib, >125A and Ib/Ip>0.5, stable arc and sound weld can be obtained. (3) In case tp/tps<0.5, an extremely stable arc can be obtained, because base current Ib can be selected to a proper current in steady welding current and besides one pulse-one droplet transfer is sustained. (4) Even if the average current Iav is kept constant, depth of penetration and fused area increase with an increasing Ip and with an decreasing tps. (5) Mechanical properties of butt welded joints obtained by pulsed current are equal to those by steady current.
Multi-electrode arc welding method is applied to the high speed one-side welding of 1mm thick SUS 304 sheets. Under welding speed lower than 6.5m/min, fine one-side welding joints are obtained by setting the final preheating electrode close to the penetration bead forming electrode so that the arc blow occurs by magnetic interaction between double electrodes. But, stable penetration bead can not be formed by the same condition under higher welding speed. So, in the case of very high speed one-side welding, by setting the distance between both electrodes about 50mm and forming the final preheating bead to gouging type, favorable welding results are established.
Both the contents of oxygen and nitrogen in the weld metal which were obtained by the submerged arc welding with various welding speeds in the argon atomsphere and the influence of the gas contents on the impact values of those weld metals were investigated. The results obtained are summarized as follows. (1) The oxygen content in the weld metal increases as the welding speed increases, and the oxygen content in weld metal is given by the following formula. O=MVx Where O: Oxygen content in weld metal (ppm), V: Welding speed (cm/min), M, X: Constant. (2) The Si, Mn and C contents approach the calculated values (the average values of the consumed wire parts and the molten steel plate parts) as the welding speed increases. (3) The nitrogen content in the weld metal is almost constant irrespective of the welding speed. (4) The absorbed energy by the charpy impact test decreases as the welding speed increases, and this is given by the following formula. E=KV-n Where E: Absorbed energy (Kgf-m), V: Welding speed (cm/min), K, n: Constant. (5) The weld metal obtained in the argon atmosphere had higher oxygen content and lower nitrogen than those obtained in the air. (6) In average, the absorbed energy of the weld metal obtained in the argon atmosphere were similar to those in the air with some exceptions.
The submerged arc welding in variously mixed argon-oxygen gas atmosphere was studied experimentally. The effects of oxygen partial pressure were investigeted. Especially the effects on oxygen and nitrogen contents of the weld metal by various oxygen partial pressure were measured. The influence of oxygen partial pressure on the absorbed energy by Charpy impact test of these metals were also investigated. The results obtained are summarized as follows. (1) The oxygen content in the weld metal continues to decrease up to 0.015 MPa of oxygen partial pressure. After oxygen partial pressure exceeds this value, the oxygen content of the weld metal begins to increase again. (2) The nitrogen content in the weld metal does not change remarkablly irrespective of oxygen partial pressure. (3) The absorbed energy of weld metal continue to increase up to 0.015 MPa of oxygen partial pressure.After the oxygen partial pressure exceeds this value the absorbed energy of the weld metal begins to decrease again. A colse correlation between absorbed energy and oxygen content of the weld metal was found.
Effects of melting conditions and atmospheres on the nitrogen absorption of tungsten arc-melted iron and stainless steel were studied. With the increase of the arc current, the nitrogen content of the melted stainless steel decreases, while that of the melted iron is nearly constant. In both of the two melted metals, the nitrogen content depends hardly on the specimen weight and the gas flow rate. In each of them, the nitrogen content increases with the melting time and then reaches the saturated value which increases with the nitrogen partial pressure of atmosphere. The nitrogen absorption of the arc-melted metal was discussed with equilibrium data and was compared with the gas tungsten arc weld metal.
For the analysis of microstructure in the transition zone occurring in weld metal near base metal in welding dissimilar metals, Transition Zone Transformation (TZT) diagram was proposed, which gives the distribution of liquidus, solidus and transformation temperatures in the transition zone. As an example, the distributions of Cr and Ni measured in the transition zone between 2 1/4 Cr-lMo steel and type 309 overlaid metal were combined to Fe-Cr-Ni phase diagram to draw its TZT diagram. Further, the combination of the TZT diagram with the temperature distribution during overlaying yielded the elucidation of formation mechanism of austenite coarse grain-boundary as the site of hydrogen disbonding. The proposed mechanism was confirmed experimentally, and could be stated as follows: The austenite (γ) grains at the fufusion boundary in HAZ formed in δ→γ transformation during cooling are going to grow into the overlaid metal. Before that, however, other γ grains has already nucleated and being growing into the transition zone by the reaction of liquid→liquid+δ→liquid+δ+γ during solidification. Therefore, when the γ grains from HAZ grow only a little into the overlaid metal both the γ grains from HAZ and in the overlaid metal collide with each other in the transition zone, and this collision makes γ grain-boundary parallel to the fusion boundary. This r grain-boundary shifts a little accompanying the disappearing of δ during cooling, and the zone between the γ grain-boundary and the carbide layer formed after PWHT is regarded as so-called γ coarse grain.
Effect of delta ferrite on low temperature toughness of molbdenum-bearing weld metal (Type 316L) was reported in authors' previous papers, which revealed that notch toughness of as-welded metal was considerably dependent on a solidification mode and in addition, the amount of molybdenum within the delta ferrite which was strongly affected by the solidification mode was closely related to the weld toughness. In this study, a similar relation on molybdenum-free weld metal (Type 308L) was investigated in detail by using a transmission electron microscopy (TEM) and an analytical electron microscopy (STEM/EDX). From notch toughness test at 77K of as-welded metal, the toughness decreased monotonously and slightly with increasing amount of delta ferrite. This result differed from the previous data of Type 316L weld metal and revealed that toughness of Type 308L weld metal was basically unaffected by solidification mode. In eutectic delta ferrite, a loss of coherency between crystallographic orientation of delta ferrite and that of adjacent austenite matrix reduced as compared with previous data of Type 316L weld metal. Moreover, STEM/EDX analysis suggested that chromium content within eutectic delta ferrite was about 4 percent more than that within primary delta ferrite. This was considered to be due to difference of solidification mode. From above results, lack of molybdenum in the weld metal would increase coherency at eutectic delta ferrite/austenite interface. As a result, marked degradation of toughness in eutectic delta ferrite weld metal was considered to not occur.
Effects of solution temperature and sensitization time on the stress corrosion cracking (SCC) cf type 304 stainless steel were studied in high temperature water at 562 K containing dissolved oxygen of 8 ppm, using the slow strain rate testing (SSRT) technique at the strain rate of 4.17×10-6 s-1. For the specimen solution-treated at 1373 K, the SCC drastically occured by the sensitization treatment at 923 K for 7.2 ks. but the SCC hardly occurs even at 100 ks of sensitization time for the specimens solution-treated at 1473 K and 1573 K. For the specimen solution-treated at 1373 K, the size of grain boundary carbides and the width of attacked grain boundaries after sensitization treatment of 7.2 ks, are larger than the size and width solutiontreated at 1473 K and 1573 K according to transmission electron microscopy and Strauss test. The corrosion rates of grain boundary attack on Huey test increased with the holding time in solution treatment at 1373 K for both the solution-treated specimen and the sensitized specimen after solution-treated. The results suggest that impurity elements segregate to the grain boundaries during solution treatment at 1373 K, and accelerate the precipitation of grain boundary carbides during sensitization. The SCC occurs under the presence of both the Cr depleted zone by the sensitization and impurity elements at grain boundary.
The effects of carbon on the strength and ductility of the electron-beam-welded joints of powdermetallurgy molybdenum were investigated systematically. Carbon addition of 0.0015 to 0.0093 wt.% was performed by a series of pre-or postweld carburizing. The materials were electron-beam-welded by a meltrun technique. Tensile tests were performed at temperatures -100 to 20°C with a strain rate of 1.2×10-3 s-1. The fracture surfaces were observed by a scanning electron microscopy. The fracture mode, crack generation and propagation characteristics and distribution of precipitates were examined. At relatively low temperatures, the optimum carbon content to improve the ductility was 0.0015 to 0.0093 wt.% for the preweld heat-treated molybdenum, whilst 0.0015 wt.% for the postweld heat-treated one. Particularly, the preweld carburized specimen with more than 0.0030 wt.% carbon showed a ductility as high as the base metal with an equivalent carbon content. At relatively high temperatures, on the other hand, the ductility of the welded joint was wholly lower than that of the base metal. However, degradation in the ductility was the least for the preweld carburized specimen with 0.0093 wt.% carbon.
The effect of stress on the types of fracture surfaces of reheat cracking was investigated on three grades of heat resisting steels; 1Cr-1/2Mo, 2 1/4Cr-1Mo and 1/2Mo steels. The modified implant test method was employed for a constant load condition. Two types of fracture surfaces were recognized; an intergranular and a transgranular types, depending on the magniturd of the stress. When the restraint stress was high, the crack initiated at an earlier stage of reheating and the intergranular type appeared. At this stage, the prior-austenite grain boundaries were embrittled by the phosphorus segregation. When the stress was low, the crack initiated after a long lapse of time in the holding stage at 873K. In this stage, the percentage of intergranular fracture surface was decreased with increasing the lapse of time by the reason that phosphorus formerly segregated at the grain boundaries diffused back into the grain interior. The phosphorus concentration in the grain boundaries was increased by the stress in both the earlier stage of reheating and the holding stage at 873K.
This paper deals with parameters which dominate residual stress produced by bonded two dissimilar materials. Parameters were derived from theories of elastisity and heat conduction. The validity of parametrers was proved by using Boundary Element Method (BEM). The residual stress at the neighbourhood of bond line in similar body is the same value at a point of similarity. This conclusion is important for making clear the effect of a specimen size on a material strength.
The extension force of short cracks or initial defects existing in the inelastic field of notches can be evaluated by, J-integral. The solution of J-integral may be obtained by interpolation method using elasto-plastic stress. In this case, if the elasto-plastic stress distribution in notch field is estimated by using only elastic solution, then J-integral is calculated by only elastic analysis of components. Thus, in the present report, the distribution of elasto-plastic stresses in notch field were estimated by using elastic solution. For this approach, strain energy density was taken as the intermediary quantity which connect elastic and elasto-plastic states. The estimating equations on the intermediary quantity were derived by combining the extending of Neuber's rule and elasto-plastic FEM. The distributions of elasto-plastic stresses were calculated from the strain energy density. By taking strain energy density as the intermediary quantity, it was able to consider stress redistribution by local yielding, and to consider multiaxial stresses in the notch field. As a result, equivalent and principal stresses could be estimated with mechanical validity in the inelastic field of notches.
In order to assess the growth rates of initial cracks in inelastic notch fields by cyclic loads, it is inevitable to apply clasto-plastic fracture mechanics. In the present report, the evaluating method of ΔJ was developed for the initial fatigue cracks in the inelastic notch fields. The interpolation function for calculation of J-integral by Willson was modified for application to the notch fields. In the calculation of J-integral stress gradient was considered in the notch fields without cracks. Fully reversed fatigue tests were carried out on the notched strips of HT80 and A5083-O. The crack closure behaviors in the notch fields were observed. The approximating equations were formed to predict crack opening ratios in the notch fields. The fatigue crack growth rates in the notch fields were plotted to ΔJ. As the results, it was cleared that the present ΔJ is applicable to assess the fatigue cracks in both the elastic and inelastic notch fields. And then, the phisical meaning of ΔJ was discussed.
Round bar tension test, Charpy V impact test and static 3-point bending test as well as ultrasonic attenuation and wave velocity measurements are made by using carbon steel heat treated with various conditions. Those tests are carried out for the purpose of establishing the nondestructive methods for material property characterization. Correlations between results of material tests and ultrasonic attenuation or wave velocity are examined. Relationships between yield strength, ultimate strength or elongation percentage and attenuation coefficient are represented by smooth curves. Yield strength as well as ultimate strength decreases and elongation percentage increases with increasing attenuation coefficient. Relationship between Charpy V notch impact energy absorption in the upper shelf region and wave velocity is represented approximately by a straight line. Upper shelf energy absorption increases with increasing velocity. Relationship between critical COD and attenuation coefficient is represented roughly by a straight line. Critical COD increases with increasing attenuation coefficient. Using the results above mentioned, mechanical properties such as strength, elongation and fracture toughness can be estimated nondestructively from ultrasonic attenuation or wave velocity.