Various aluminum alloys and SUS304 stainless steel are welded explosively inserting SUS304 intermediate plate between aluminum alloy driver and SUS304 base plates. Microstructure at the welded interface and weldable conditions are decided in the present investigation. Reacted inferfacial zone is generated at the Al/SUS304 interface and it is composed of fine eutectic structure of Al and Fe4Al13 generated by cooling from a molten interface. Aluminum content at the reacted zone is higher than that the predicted value considering the energy required for the melting of each component. Such a high aluminum content phase is generated by an intensive deformation in a soft component aluminum. Weldable region for each aluminum alloy is decided by the parameters of kinetic energy lost by collision and collision velocity, and the area of weldable region is decreased by increasing the yield stress of aluminum alloy.
The combination of welding condition (optimum welding condition) which produced maximum tensile strength of S45C carbon steel friction welded joint under the notched tensile test specimen condition was investigated using response surface method. As a result, the combination of welding condition to yield maximum tensile strength at the weld was attained through a steepest ascent path. And, a second-order equation predicting the weld strength was accurately established. By the result of confirmation experiments using the predicting equation, a successful weld was obtained under the optimum welding condition. But, the optimum welding condition requires comparatively larger burn off quantity. Therefore, it is needed to consider a economical view such as less burn off quantity. Moreover, the observation of the successful welds showed that a fine grain ferrite perlite layer having comparatively low hardness widely distributed over the heat affected zone of the weld.
Effects of thermal and physical properties of materials on the transient response of temperature to a step change in welding speed were investigated using TIG arc welding and FEM calculation of three-dimensional heat coduction. The materials used in this study were stainless steel, mild steel, aluminum alloy, brass and copper 9 mm in thickness. In TIG arc welding of low heat-conductive materials, large difference in maximum temperature appears in the period between former quasi-state and latter one. On the other hand, high heat-conductive materials indicate large difference in temperature gradient, but a little change in maximum temperature. In addition, the high heat-conductive materials require longer distance or time to be in latter quasi-state. The transient response from former to later quasi-state is characterized by the fraction of maximum temperature and temperature gradient to those at both quasi-states. These experimental results are confirmed by FEM calculations based on three-dimensional heat conduction. It is also clarified that although the maximum temperature mainly depend upon the thermal conductivity and thermal diffusivity, the transient response is dominated only on the thermal diffusivity. Therefore, the high thermal diffusive materials show slower response to a step change in welding speed.
This paper summarized metallurgical and mechanical properties of stainless steel SUS316L joints brazed with three types of newly developed palladium-copper based filler metals, 30Pd-60Cu-10Co, 30Pd-60Cu-10Ni, 30Pd-50Cu-10Ni-10Co, and commercial nickle-based filler metal Ni-Cr-W-Fe-B-Si. The results obtained were as follows: (1) The maximum joint strength at room temperature was the joint brazed with the palladium-copper based filler metal 30Pd-60Cu-10Co, and the mean value was 536 MPa at the joint clearance range from 0.07 to 0.15 mm. (2) The 30Pd-60Cu-10Co filler metal showed the highest joint strength at 473 K, and the 30Pd-50Cu -10Ni-10Co filler metal showed the highest joint strength at 673 K, 873 K, and 1073 K. (3) Joints brazed with 30Pd-60Cu-10Ni have superior creep rupture resistance at 673 K, and the brazed joints with Ni-Cr-W-Fe-B-Si offered longer rupture time at 1073 K than those with palladiumcopper base filler matals.
This paper summarized metallurgical and mechanical properties of stainless steel SUS316L joints brazed with two types of newly deve10ped palladium-nickel based filler metals, 40Pd-5ONi-10Co, 30Pd -50Ni-10Cu-10Co, commercial palladium containing filler metal, 33Pd-64Ag-3Mn(BPd-10), and nickle-based filler metal, Ni-Co-Cr-Mo-Fe-B. The main results obtained were as follows: (1) The maximum joint strengths at room temperature were the joints brazed with the palladium-nickel based filler metal 40Pd-5ONi-10Co and 30Pd-5ONi-10Cu-10Co, then the mean values were 516 MPa. (2) The 30Pd-5ONi-10Cu-10Co filler metal showed the highest joint strength at 873 K or below, and the 33Pd-64Ag-3Mn filler metal showed the highest joint strength at 1073 K. (3) Joints brazed with 40Pd-5ONi-10Co and 30Pd-5ONi-10Cu-10Co have superlor creep rupture resistance at 673 K and 873 K, and the brazed joints with Ni-Co-Cr-Mo-Fe-B offered longer rupture time at 1073 K than those with palladium-nickel base filler matals. (4) The 30Pd-50Ni-10Cu-10Co filler metal is the best filler metal for heat-resisting brazing.
The modelling of weld pool oscillation is carried out in order to make clear the natural frequency and the oscillation mode of the pool in the fully penetrated welding of thin plate. The oscillations of the elliptical pool are discussed because the molten pool in the traveling arc welding takes the oval shape. In the case of the elliptical pool with a finite depth having both a top surface and a bottom surface, the dispersion relation between the natural frequencies, the pool shape, the surface tension and the density of the melted metal is derived.
A spin electrode system was developed to improve the electrode tip life in spot welding of coated steel sheets. This method features a periodically rotating electrode which is inclined in relation to the force axis. This electrode rotation introduces a type of self-dressing action to the electrode tip and, therefore, delay tip wear. Electrode tip life tests conducted by using a prototype equipment clearly indicated superiority of this system over the conventional spot welding method and an approximately 20 times electrode life was achieved for a galvannealed steel (60/60g/m2).
An attempt was made to improve the electrode tip life, which has been a major concern in spot welding of coated steel sheets in automobile assembly lines. Spin electrode spot welding is newly developed. In this spot welding, longer electrode lives are achieved since an electrode tip surface is effectively used by forming multiple contact points and, further more, the successive movement of the contact point provides a type of "self-dressing" action on the electrode surface. The electrode rotation angle of 60° is found to be the most effective on the improvement of electrode tip lives when a radius type electrode of 15R was used and this electrode was inclined at 10°in relation to the force axis. Under this condition, approximately 20 times longer electrode tip lives are achieved irrespective of coated steel types and evaluation test methods.
In the previous report, mass spectroscopic measurement showed that helium was concentrated at the arc axis of argon-helium gas tungsten arcs. In this report, a method was proposed to measure the position-dependent composition of the demixed arc plasma by using a monochromator. The composition and temperature of argon-hydrogen, argon-helium and argon-nitrogen gas tungsten arcs could be deduced from the intensity ratio of the ArI and ArIl lines in the LTE plasma. When helium or hydrogen gas was added to an argon arc, the additional gas was found to significantly concentrate at the arc plasma axis. The demixing ratio of the helium in the arc core was the same as that measured previously using mass spectroscope. When nitrogen was added to the argon plasma, a slight concentration of nitrogen at the arc core was also observed. Furthermore, the results obtained suggest that the arc plasma temperature at the arc core decreased upon introduction of hydrogen gas.
The fundamentals of laser beam drilling were studied using a high peak pulse CO2 laser. Specifically, those areas examined were the effects of the beam-plasma interaction and heat accumulation near the irradiation point during multipulse irradiation on the characteristics of drilling Si3N4 ceramics and acrylic resin (PMMA). In the case of beam-plasma interactions, the drilling efficiency and hole shape were compared in a vacuum and in air. For heat accumulation, holes formed with a few pulse frequencies, which had enough time to cool, were compared with those formed at higher pulse frequencies. The results revealed that in the case of drilling Si3N4 in air, beam scattering by the plasma plume decreased drilling efficiency and increased the hole diameter. Also, decreasing the pulse duration or drilling in a vacuum can successfully improve the drilling efficiency. Furthermore, in PMMA, the hole diameter of low aspect ratio holes were greatly increased by heat accumulation, and as the aspect ratio increased there was a significant increase in hole diameter caused by the beam scattering by the plasma plume.
A new complex arc welding process is proposed. The aim is to achieve higher production efficiency and higher welding quality required in a small batch production. The process combines some element welding to obtain optimum multi-layer weld. The element weldings are conventional TIG, MIG (MAG), and their add-on function versions using filler wire(s) and magnetic control together. The process selects appropriate element welding for each individual pass considering the characteristics of bead formation. The application of the element weldings to the stainless clad steel has been investigated to obtain the fundamental data, such as the bead formation, weld metal, pass numbers and mechanical properties. Experiments showed the following results. Some combination of two element weldings reduce the penetration compared with conventional TIG or MIG welding, resulting in decreased dilution of elements in stainless steel. The deposition rate rises without spoiling welding speed and operability. The Ni and Cr contents in the weled metal of the TIG added with a filler wire and magnetic control is higher than that of TIG welding. The tensile fracture of welds in the complex process occurred in the portion from the base metal to HAZ, and that in the single process occurred in the base metal. The tensile strength of welds in the complex process is equal of in the single process, and its value is equal or larger than the stainless clad steel base metal. The peak of the hardness in the weld metal is lower and narrower.
The electric current flowing from an anodic spot was obtained by measurement of the amplitude of the electric potential difference between two points on the back of a thin plate, when the anodic spot was rotating on the circular weld pool formed in a stationary GTA welding. As a result, the anodic spot current on the molten pool in an austenitic stainless steel plate was at most 10% of the welding current and was not more than that of the steel plates in which at least Cr was not included. When welding current was increased more than 180-200 A, the anodic spot current in the stainless steel plate decreased to a few amperes. When the tip of a composite oxides rod (55%Al2O3+41%SiO2) is touched to the arc from a side of the pool and the melting and vaporizing oxides bit is being transferred on the pool surface to the opposite side, a part of welding current flows from the oxides. The current depends on the composition of the base metal. The order of the base metals in which the current flowing from the oxides bit was higher was cold rolled mild steel, pure iron, stainless steel with high S content, stainless steel with low S content, and Ti-alloy(8Al-Mo-V). From those experimental results, it was clear that the anodic spot current was greatly influenced by the lowest ionization potential in the main elements of the base metal and the vaporization behaviour on the molten pool. In the GTA welding of cold rolled steel plates in which the anodic spot current was higher, the possibility of periodic variation in temperature near the weld pool and irregular weld bead formation caused by the anodic spot movement on weld pool were estimated from thermal conduction analysis, and several examples were given for a thin plate welding.
Solidification crack susceptibility in partially-melted bead-on-plate laser beam weld metal of 6 mm trick 0.2C-1.8Ni-0.55Cr-0.2Mo low alloy steel has been investigated with change of S and P contents in steel using maximum 5 KW CO2 laser facility beam welder. Effect of weld bead configuration and amount of S and P on crack length in crosssectional bead have been mainly investigated. Estimation of crack length in weld metal was tried by means of regression analysis of data, using bead configuration and impurities of S and P. Moreover, effect of restraint of weld bead during welding on crack susceptibility was investigated. Main results obtained are as follows; 1) Weld bead configuration is gradually changed from winecup-type to well-type with changing to higher power and higher welding speed in laser beam welding (LBW) within the welding condition in this investigation. 2) With an increase in weld power and welding speed solidification crack susceptibility in weld bead is increased. 3) Solidification cracks have been seen both winecup-and well-type weld bead. However, the cracks were much more in well-type bead than in winecup-type bead in general. 4) S and P impurities in steel have a detrimental effect for the cracks. However, S is 1.8 times more detrimental than P according to statistical investigation. 5) According to statistical investigation the cracks increase with an increase in length of side wall fused and of dB1/2 (bead width in 1/2 penetration) 6) The equation which can estimate the crack length in weld bead is introduced from the statistical investigation using the factors of bead configuration and impurities (S, P) in steel. 7) The restraint of the specimen during welding increases the crack susceptibility in weld bead in comparison with the restraint free bead.
Fractographic investigation of microcracks in a real multi-pass weld metal of Ni-base alloys was carried out in order to find out the factors which caused microcracks in this study. Two modes of microcracks, viz., liquation crack and ductility-dip crack were observed in reheated zones of weld metal. According to the EDX and AES analyses on fracture surface of these cracks, not only Nb and Mo in microconstituents but also P, Si and Senriched on thefracture surface. The cross-bead varestraint test was performed in order to make clear the effects of impurity elements such as P, Si and S on hot cracking susceptibility of reheated weld metal of Ni-Cr-Fe ternary alloys. Base metals used were basically 70%Ni-Cr-Fe ternary alloys in which Cr contents were varied from 0 to 20%. P, Si and S contents were independently varied in the ranges of 0.002-0.032%, 0.05-1.02% and 0.001-0.02%, respectively. Although the liquation cracking susceptibilities of all materials used were too low, they increased with an increase in impurity elements. On the other hand, in the case of ductility-dip cracking, cracking susceptibilities of materials containing S were much higher than those containing P and Si. Especially cracking susceptibilities of Ni-30%Fe and Ni-20%Cr-10%Fe alloys containing 0.007%S were higher than those of Ni-5%Cr-25%Fe and Ni-10%Cr-20%Fe alloys. It followed that the ductility-dip cracking susceptibility of reheated weld metal of 70%Ni-Cr-Fe alloy was affected as a function of interaction of Cr and S contents in weld metal.
Hot ductility testing of weld metal was performed in order to make clear the mechanism of ductility-dip cracking in weld metal of 70%Ni-Cr-Fe ternary alloys containing 0.007%S in which Cr contents were varied from 0 to 20%. The temperature range of testing was varied from 873 to 1473 K. Microstructures and fracture surfaces were also examined. The ductility at 1173 K of Ni-10%Cr-20%Fe alloy was higher than those of Ni-30%Fe and Ni-20% Cr-10%Fe alloys. It followed that these ductilities were related to the ductility-dip cracking. Fracture modes of this testing samples were almost intergranular fracture. According to the microstructure examination, grain boundary carbides, M23C6 appeared in only Ni-20%Cr-10%Fe alloy weld metal at the temperature of 1173 K. Hardness in weld metal increased with an increase in Cr content. On the other hand, increasing in holding time at 873 K decreased a ductility of the base metal of Ni-30%Fe containing 0.007%S at 873 K. It followed that S easily segregated on grain boundary in low Cr alloy. These results meant that optimum Cr content in weld metal was necessary in order to reduce the ductility-dip cracking susceptibility because of contrary effects due to grain boundary carbide, hardness and grain boundary segregation of S.
In an oxidizing gas welding atmosphere of argon-based Ar-CO2-O2 gas mixture, weldings were carried out, using a popular Fe-Si-Mn electrode wire (YGW 12) and rolled steel for welded structure (SM 400B). Mechanical properties such as ultimate tensile strength and Charpy impact property for the extremely low oxygen steel weld metal which oxygen level is 0.001-0.025 mass/ have been investigated. The ultimate tensile strength seems to be governed principally by alloy content of weld metal, and small amount of oxygen in weld metal has only a minor effect on the ultimate tensile strength. The higher alloy content, the higher the ultimate tensile strength. The extremely low oxygen steel weld metal has greater tensile property, because of limited amount of oxidation losses of alloying elements such as carbon, silicon and manganese. The Charpy toughness of steel weld metal has been affected by the oxygen content in weld metal. High toughness obtained in two oxygen levels, one is 0.04-0.05 mass% oxygen which is well-known peak and the other is less than 0.002 mass% oxygen. It is very important that the Charpy impact property has been improved in the extremely low oxygen steel weld metal which oxygen level is less than 0.002 mass%.
Friction welded butt joints are widely used as machine members and structural elements, but valid evaluation method of the joint performance, especially under service load conditions, has not been established yet. Evaluation of corrosion fatigue behaviors of the joint is one of the important problem, for some joints are used in pollutive environments. In our previous paper, corrosion fatigue behaviors in artificial seawater were investigated on S25C/S25C friction welded butt joints. The results indicated that the S-N curve for corroision fatigue strength of the joint specimen showed steeper slope than that of the base material and the strength of the joint took almost the same value as that of the base material specimen in long life region, and the scatter of fatigue lives became smaller in accordance with the increase in fatigue life contrary to the case of the base material specimen. Detailed observations of corrosion pits and non-propagation cracks of run-out specimens suggested that the above mentioned corrosion fatigue characteristics of the joint was governed by corrosion pits generated preferably on exposure surface of the transitional plane of fiber flow directions developed at the final stage of friction welding process. The present study was carried out to clarify the corrosion behaviors of the joint in more detail. Joint specimens were immersed in artificial seawater at stress free condition during 5 and 10 days. Distribution of corrosion pits near the weld interface and geometrical factors of pits were evaluated precisely, and the difference of corrosion behaviors between the joint and the base material were also discussed. The results of this study gives valid support for the estimation on the corrosion fatigue characteristics of the joint indicated in our previous paper.
Results of valence AES analyses, which have been performed for transient-metal/ceramic interfaces by the authors, are surmarized in the present study. Atomic interactions at the interfaces are discussed by using thermo-chemical data. The data do not give a consistent full explanation of all. A simple jellium model is introduced to interpret them. The interactions are systematically discussed from views on two extremes of electronic property.
In the previous report, it was indicated that the usage of 19Cr-2Mo-0.25Zr steel filler metal for the first layer and 30Cr-2Mo steel filler metal for the upper layers respectively was effective to ensure a good weld ductility in the overlay welds of the 30Cr-2Mo steel cladding steel. The corrosion resistance of the overlay welds is also important in the practical use of this material. Therefore, the corrosion resistance in such overlay welds has been investigated in this report. The corrosion resistance was compared with ones of 30Cr-2Mo steel base metal and cladding metal of 30Cr-2Mo clad steel. Measurement of anodic polarization curves and pitting corrosion potentials, grain boundary corrosion test, stress corrosion cracking test and crevice corrosion test were performed. The excellent corrosion resistance, which was almost same level as ones of 30Cr-2Mo steel base metal and cladding metal of 30Cr-2Mo clad steel, was obtained by using 19Cr-2Mo-0.25Zr steel filler metal for the first layer and 30Cr-2Mo steel filler metal for 2nd, 3rd and 4th layers. On the basis of these results, the overlay welding procedure by using 30Cr-2Mo steel filler metal for the upper 3 layer after using 19Cr-2Mo-0.25Zr steel filler metal for the first layer was recommended in order to ensure a good corrosion resistance of the overlay welds.
The optimum welding conditions for overlay welding of 30Cr-2Mo clad steel with 19Cr-2Mo-0.25Zr steel filler metal for the first layer and 30Cr-2Mo steel filler metal for the upper layers have been investigated. Mechanical properties of the overlay welds of 30Cr-2Mo clad steel with these filler metals have also been examined. Experimental results have shown that an automatic TIG welding, which can provide a constant penetration ratio on overlay welding, was a suitable method for the fabrication of a device in the chemical plant made of 30Cr-2Mo clad steel. Mechanical properties like as tensile stress, elongation and bend ductility of the overlay welds fabricated with 19Cr-2Mo-0.25Zr steel filler metal for the first layer and 30Cr-2Mo steel filler metal for the upper layers on a low alloy steel, respectively, were satisfied with ones specified in the JIS standard. The notch toughness of the overlay welds was almost same as one of 30Cr-2Mo steel base metal and the cladding metal of 30Cr-2Mo clad steel. In addition, the test results of cold-working and hot-working, which was indispensable to the fabrication of a device in the chemical plant, have indicated that 30Cr-2Mo clad steel had an excellent formability.
Effect of the reaction layer formed at the bonding interface on the tensile strength of Si3N4-molybdenum joints using copper-base active insert metals was examined in order to discuss the governing factors of the bonding strength and to improve the bonding strength by controlling the reaction layer thickness. The bonding joints were completed in vacuum (6 mPa) at 1573 K for 0-4.8 ks to vary the reaction layer thickness. The tensile strength of joints was, risen up to about 100 MPa, 90 MPa and 120 MPa (at R.T.) by maintaining the reaction layer thickness at around 40 μm, 2 μm and 4 μm with Cu-5%Cr, Cu-1%Nb and Cu-3%V insert metals, respectively. The fractured modes shifted from the interfacial fracture to the brittle fracture in reaction layer with increase in the reaction layer thickness. In case of the optimum reaction layer thickness, the fractured surfaces were comprised of the regions fractured in the reaction layer and at the interface between Si3N4 and the reaction layer. The elevated temperature tensile strength of joints bonded using Cu-5%Cr insert metal increased to the maximum value approx. 125 MPa (at 473 K), as the testing temperature was increased from R.T. to 473 K, and then fell down contrarily with rising the testing temperature.
The overall objective of this project was to provide a date showing how carbide powder in addition to metal powder can be used effectively to increase the hardness of overlay composite alloy and hence increase resistance to abrasive wear. An experimental study was performed to examine of combination of metal powders and reinforcing powders. The metal powders considered were stainless steel powder, Ni-base alloy powder, Cobase alloy powder and high speed steel powder, and reinforcing powders considered were metal-carbide powders and ceramic powders. Carbide and ceramic dispersion type overlay composite alloys were produced by plasma transfer arc powder welding. The overlay composite alloys were consisted of matrix and carbide powder fused with base alloy metal and forming eutectic structure, and non-fused carbide particles which are the partially melted reinforcing powder. The average hardness of matrix depended on the kind of base metal powder and the existence of reinforcing powder. The average hardness of matrix for high speed steel powder was higher than other powders used, but the hardness of other powders used, increased with addition of reinforcing powder compered to each base alloy metal only without addition according to fused the powder. To assess the resistance to abrasive wear of overlay composite alloy a rubber wheel abrasion test was performed on its surface. Weight loss of overlay composite alloy by wear was decreased more with addition of reinforcing powder than base alloy metal only without addition of its powder due to the existence of non-fused carbide particles in it. Especially, the abrasive wear resistance of composite alloys depended on the increase in the volume fraction of non-fused carbide particles. The addition of carbide powder, especially Ti-carbide, to base metal powder can be used effectively to increase the hardness of overlay composite, and hence increase resistance to abrasive wear of it.
This study was concerned with the production of carbide dispersion type composite materials by plasma transfer arc welding. The composite materials were produced by introducing different amounts of Cr-carbide and/or Ti-carbide powders in Co-base alloy (Stellite 6). To assess the resistance to wear of the composite materials, rubber wheel abrasion test was performed on surface of the composite materials. The composite materials were consisted of Co-alloy matrix and non-fused carbide. The average hardness of matrix was increased from HV450 to HV850 according to Cr-carbide content of the composite material. Weight loss of composite materials by wear were decreased from 850 mg to 50 mg according to volume fraction of non-fused carbide particles. Especially when mean free path between carbide particles was smaller than size silica sand (wear material), abrasive wear resistance of composite materials was rapidly improved.
Co-base alloy (stellite) powders were dynamically compacted by using cylindrical axisymetric explosive method. The E/M ratio (where, E is explosive mass and M is powder mass) and the particle size of the powder were varied to investigate their effects on compaction. Optimum compact, where no cracks was obtained at the E/M ratio between 2.5 and 3.0 using 75μm/100μm (M designation) and 125μm/150μm (L designation) powders ; the specific density of compacts exceeded 98%. Satisfactory compacts could not be obtained using a size powder<50μm (S designation).
In the previou study, it was shown that transformation superplasticity was more effective to reduce the deformation stress than transformation expansion under some conditions and the transformation temperature was concerned in the deformation stress in the midst of cooling. In the present report, the elongation of specimen was invesigated during transformation at a constant stress in order to clarify the basic behaviour of transfomation superplasticity. The results are shown as follows ; 1) During transformation a specimen was plastically distored by a small stress of the order of 1 MPa. 2) The displacement by superplasticity transformation is in proportion to the applied stress during transformation. The inclination, however, varied with materials. 3) If the strength restoration module is taken as R and the deformation strength (σ) is writen as σ=εR, R was about 9.0-16.6 GPa that was 1/10-1/20 times as much as Young's module. 4) In the tensile test of the specimen during martensite transformation at room temperature, the specimen was plastically distored by less than quarter of the fracture stress and the strain by applying a small stress of the order of thermal contraction gave rise to martensite. Then the surface relief by martensite was observed.
In the previous reports, the proportion between transformation superplasticity and transformation expansion on the amount of the stress releasement was examined. And then, the appropriate conditions (transformation temperature) which made most use of the stress releasement in welding by transformation superplasticity was obtained. During transformation, a speciemen was plastically distorted by a small stress of the order of 1 MPa. On the other hand, to decrease angular distorsion and residual stress is very important for welding design and fabrication. There are, as well-known, many countermeasures (weld heat-input, preheating, postheating, peening and so on) to reduce them. In the present report, the trial welding rods with many kinds of transformation temperature were made and the effect of transformation temperature on angular distortion in welding was examined. The results are shown as follows; 1) Under the condition of a constant heat input, transformation temperature has an important effect on angular distortion in welding in spite of its weld length. 2) The transformation starting temperature which is most effective to reduce angular distortion is 250-300°C (in this case interpass temperature and preheating temperature is 150°C). 3) There is respectively the best interpass temperature and preheating temperature for each weld metal with transformation temperature to reduce angular distortion. 4) Transformation temperature was moved by the dilution with base metal or prepass weld. So, an effect of dilution is important for single pass welding and so on.
Fatigue tests have been performed on fillet welded joints between piping and sockets so as to investigate the effective factors such as welding methods and leg length of welds. The used materials were structural steel (S25C) and carbon steel pipe for pressure service (STPG38). The applied welding methods were GTAW and SMAW. Two types of covered electrodes were ued like as low hydrogen type and ilmenite type for SMAW. The following conclusions are obtained. (1) As a matter of course, the fatigue strength of the joints by GTAW was higher than that of the joints by SMAW. And the fatigue strength of the joints by low hydrogen type covered electrode was higher than that of the joints by ilmenite type. (2) The critical size S/T (S: leg length, T: base metal thickness) was about 1.2. (3) In case the maximum tensile stress of the welded joints exceeds 147 MPa, it is better to select butt joints rather than fillet jonts.
The basic fatigue strength of welded joints has been investigated on three kinds of steels. Specimens were 20 mm thick, 50 mm wide 500 mm long transverse butt welded joints made by submerged arc welding. The maximum applied stress was held constant to be the yield strength of materials, while the minimum applied stress was varied with the stress range in order to obtain the basic fatigue strength. The yield strength was varied from 284 MPa to 579 MPa. In a long life region, the fatigue strength became superior as the yield strength decreased. It is also suggested that the low yield ratio steel which can be produced by thermo-mechnical control process may have a high fatigue strength.
When three dimensional welding residual stresses are measured based on inherent strains using Finite Element Method, too many inherent strain components in elements have to be specified to express their distribution. If these are determined experimentally, measurements of elastic strains must be made for points more than the inherent strain components. In order to reduce the number of measurements and to find the general distribution pattern of inherent strains, the functions are introduced to express the distribution of inherent strains instead of specifying those in individual elements. With the aid of functions describing the distribution of the inherent strains, the total number of unknown constants can be greatly reduced. To verify this new method, residual stresses and inherent strains in bead-on-plate welds are estimated. The estimated residual stresses by simple functions show very good accuracy compared with those computed by thermal elastoplastic Finite Element analysis.
In order to clarify a cause of non-uniform deformation behaviour of austenitic stainless steel weld metals produced with high heat input, crystallographic orientation and internal strain of columnar crystals were studied. The grain structure of weld metals consists of a central band and both side arms. As the weld metal was stretched along transverse direction to the weld line, the elongation of the central band was larger than that of the side arms of weld metals. Therefore, the thinning of the central band occurred. Average value of Schmid factor of the columnar crystals in the central band with respect to the tensile direction was the same with that of side arms. While, larger internal strain is observed for the crystals in the side arms in comparison with in the central band. It is concluded that the thinning of the central band during tensile deformation is due to smaller internal strain of the central band than that of the side arms.
Fluxless bonding process with pulse heat tip has been researched and developed by inserting both plated In/Sn and Sn layers at the bonding interface before bonding. Quality improvement of the bond on the process has shown experimentally to be realize by inserting the thin Sn/In plated film on the surfaces of the lead and thin sheet as fine electronic materials, that is, tensile strength of the bond has been improved largely as the supply In plating layers with the thickness of 1-3μm on the Sn plated film (10μm) on the surface of Cu-Ni-Sn alloy lead, on bonding the lead and thin sheet with Sn plated film (10μm). This improvement is caused by both high oxidation resistance of Sn-In alloy and the expel of low temperature metal such as Cu-Sn-In etc from the interface of the bond during bonding. Furthermore, the effect of bonding temperature lowering is clarified in the bonding process on assemblying electronic devices on a printed circuit board.
Anodic bonding of glass and Si, which is performed by applying positive voltage of several hundred volt on Si, is well known as Mallory sealing process and has been in use. However, anodic bonding of glass and metal has not been comprehensively investigated and mechanism of the bonding has not been well understood. A fundamental study on anodic bonding of borosilicate glass and metal was carried out. Glass to Mo bonding and glass to Al bonding were successfully made, and glass to 304ss, glass to Ti, glass to Ni and glass to Au bondings were also made but they fractured at low stress level. Bonding test of glass and Mo using the design of experiment was carried out in order to specify dominant bonding parameters. Then, it has become clear that the bonding temperature and the applying voltage should be dominant in the range of bonding temperature of 400°C-600°C, applying voltage of 0 V-350 V, bonding time of 5 min-60 min, bonding pressure of 0.03 MPa-0.7 MPa in Ar atmosphere or in vacuum. Microscopic observations and chemical analysis were performed for glass to Mo bonded structure. The reaction zone between glass and Mo was not identified from the results of SEM and EPMA. Result of ESCA analysis revealed that Na, which was not found around the boundary, was detected in glass near the anode and Mo oxide was detected in glass near the boundary. Basing on the results, it has been considered that metal ions would diffuse into glass substituting for Na' and metal oxide be formed, then glass to metal bonding should be achieved.