Effects of helium gas on the maximum arc pressure and on the critical travel speed to melt a base metal were investigated in GTA welding. Results were obtained as follows; (1) The critical speed in helium (He) gas arc is much higher than in argon (Ar) gas arc. Heat input per bead length at the critical speed in He gas arc is lower than in Ar gas arc. This fact is understood because distribution of a heat source in He gas arc is more concentrative than in Ar gas arc. (2) Electrode geometry is effective on the critical speed and especially the critical speed has a maximum value at a vertex angle of 45°, when a diameter of electrode is held constant. (3) The pressure in He gas arc is much lower than in Ar gas arc and is not sensitive to electrode geometry. This fact is understood because a spreading angle of arc current in a front of an electrode tip in He gas arc is smaller than in Ar gas arc. (4) When He gas is mixed into Ar shielding gas, generally the pressure decreases, but the critical speed is held constant. This fact shows that mixed He gas has a great influence on arc phenomena in a front of electrode tip, but it has little influence on an arc column. (5) When a few litter per minute of He gas is added to an upper part of an electrode tip through a nozzle in Ar shielding gas, the pressure effectively decreases to the degree of the pressure measured in He shielding gas.
Effects of an electrode geometry on the maximum arc pressure at a base metal were investigated in GTA welding. Results obtained are as follows; (1) The pressure increases with a decrease in a vertex angle of an electrode. But at the vertex angle of 45° the pressure has a peak value and then the pressure decreases with the decrease in the angle less than 45°. (2) When a shape of an electrode tip is treated a frustum of a cone, the pressure decreases and a vertex angle is not effective on the pressure. This fact suggests that the pressure is dependent on temperature distribution near an electrode tip. (3) Arc is more concentrative at the tip by such an arc characteristic that arc generates along the shortest path between an electrode and a base metal. On the other hand, temperature at an electrode tip becomes high and arc disperses to an upper part of the electrode from the tip. As these results, the pressure has a peak value about the angle of 45°. (4) When a diameter of an electrode increases, the pressure increases usually and such tendency is remarkable at the angle of 45°. This fact is understood that a rise of temperature near the tip is prevented and arc concentrates at the tip according to increasing the diameter.
Pulsed TIG welding phenomena of mild steel, stainless steel and aluminum alloy, are investigated with respect to the welding current waveform, supplied from analogue transistor controlled power source. The pressure of TIG arc in pulsed or steady current are measured carefully, taking account of response characteristic of pressure measurement system used. Weld pool behaviour is observed by high speed photography. Results obtained are summarized as follows; (1) In pulsed TIG welding, use of pulsed current having an excessive amplitude of current causes weld defects such as humping or tunnel bead even if the average current is kept constant. (2) Occurrence of humping bead in pulsed TIG welding is dependent on pulse frequency applied. It is found out that there exists the critical pulse frequency (humping frequency) fc. At this frequency, humping occurs in minimum amplitude of current at the same average current level. (3) Humping frequency fc becomes higher as the welding speed increases if the average current is kept constant. The humping frequency of mild steel is observed to be higher than that of stainless steel or aluminum alloy under same welding condition. (4) TIG arc pressure in sinusoidal current wave varies in accordance with current waveform. Amplitude and average value of pressure fluctuation are almost kept constant in the frequency range up to 300 Hz. (5) In pulsed TIG welding, molten pool is drived to oscillate by arc pressure fluctuation due to change in welding current. The intrinsic frequency of weld pool can be found out. It depends on both pool geometry and physical properties of materials such as surface tension, fluidity and density.
A new technique of high efficiency one-side narrow-gap MAG welding was developed using simple I-groove and soft backing, and 'Uranami welding' was carried out easily with this technique. It is principal characteristic of this welding technique that 'Uranami welding' is carried out easily with DC electrode negative polarity. In case of high current welding, backing does not melt down because of using DC electrode negative polarity, therefore high speed 'Uranami welding' can be achieved. In addition, the bead surface is Ushaped and penetration into side walls is increased owing to the change of molten metal flow in molten pool to a desirable pattern by directing control gas against the tail area of the molten pool. In this report, using mild steel plate (thickness: 22 mm) and I-groove (root gap: 10 mm) the range of welding conditions for achieving suitable 'Uranami beads' was searched for by observing many 'Uranami bead' shapes and the practical utility of this welding technique is discussed. The results are as follows; 1) Using this welding technique, suitable 'Uranami bead' is achieved easily over a wide range of welding conditions. The optimum welding conditions of this welding technique is as follows; welding current arc 450A - arc voltage 35V - welding speed 26cm/min wire dia.: 1.6 mm distance between contact tip-groove bottom: 35 mm primary shielding gas: 30%Ar+70%CO2 (401/min) secondary shielding gas: 100%CO2 (30l/min) control gas: 80%Ar+20%CO2 (12.5l/min) 2) The changeable root gap range and the range of misfit of base plate within which suitable 'Uranami bead' can be achieved with this welding technique are 6-13 mm and 0-3 mm respectively. 3) Using this welding technique, 'Uranami bead' can be achieved without defects.
The effects of welding parameters and wire compositions on the droplet transfer of CO2 arc welding by flux-cored wire, have been examined by means of photograph by a high speed camera. As the welding current and the argon content in CO2 shielding gas are increased, the droplet transfer becomes more preferable; the average droplet diameter decreases and the transfer frequency increases. The wire cross-sectional shape has almost no influence on the droplet transfer. Increase of flux percentage in wire is effective in the improvement of the droplet transfer. As the increase of TiO2, Fe-Si and Al2O3 or the decrease of CaF2 content in flux, the droplets become smaller and transfer more frequently. The effect of iron powder and Fe-Mn content is almost none. These variations of droplet transfer can be mainly explained by the repulsive force of slag vaporization in the droplet suspended at the tip of the wire.
Optimum gas-assisting parameters have been determined to suppress plasma formation, and the role of the assist gas has been analized in CO2 laser welding. Results obtained are summarized as follows: (1) When the assist-gas pressure p is higher than pp, which is slightly higher than vapor pressure or surface tension pressure the plasma formation is suppressed by forcing the vapor stream going up along the laser beam axis to eject along the rear wall of the cavity, providing increased penetration depth without weld defects. The value pp decreases with increasing laser power and decreasing welding speed. The fluctuation of the penetration depth tends to increase with increasing p, since the cavity diameter is enlarged by the vapor pressure which exeeds the value for the surface tension pressure to keep the cavity stable. (2) When p is too high, a lot of molten metal flowed out of the cavity closes the cavity entrance on re-entering into the cavity due to its large mass motion, providing humping bead containing large porosities. (3) The plasma formation is also suppressed effectively at vacuum pressure range 10-20 torr, providing deeper penetration depth without fluctuation of the penetration.
In this paper, a study has been described on the factor for determining the cooling behavior of electron beam (EB) welds. It was found that the heat input calculated from welding conditions did not necessarily have a good correlation with the cooling rate in EB welding because other welding process, factors not included in heat input calculation, i.e. focal point, beam oscillation and through beam current, significantly affected the cooling behavior of welds. Therefore, the authors have proposed the weld width as the factor for estimating the cooling behavior, and investigated the relationship between the weld width and the cooling time of welds in horizontal welding position. The good correlation was observed between the weld width (Bw1/2) and the cooling time from 800 to 500°C (Δt800→500 ), as given by Δt800→500=0.75Bw/2.25. The relationship is considered fully applicable to the EB welds made in other welding positions and by other types of welding machine.
This paper describes the effect of the weld width on the toughness of electron beam (EB) weld metal. The relationship between them has been investigated on the EB welds with weld width in the range 2.6-4.6 mm, using 50 mm thick laboratory carbon steels with various C, Si and Mn content. The major results are summarized as follows; (1) The effect of weld width on the weld metal toughness of carbon steels was significant in the range of carbon equivalent (CE) 0.30-0.50% for the as-welded condition, while more than CE 0.26% for PWHT condition. Toughness could be improved with decreasing the weld width due to the formation of finer microstructure. (2) For a given weld width, the strong correlation was observed between CE and hardness of weld metal. (3) For a given weld width, the weld metal toughness of carbon steels depended strongly on hardness, and a reduction in hardness resulted in improved toughness
In this report, the effects of copper and nickel plating in advance of welding on the solid phase weldability of beryllium-copper are studied, using the so-called 25-alloy bar which contains about 2.0%Be. The results obtained are summarized as follows.  Optimum thickness of plating for welding is about 5μm in copper and 2.5μm in nickel, respectively.  Even in this process, the weldable temperature can not be reduced as low as the aging temperature.  Change of weld strength with welding time is unnoticeable in copper plated weld. But nickel plated weld often becomes weak because of occurrence of defect which looks like precipitate or kirkendall void.  By proper copper plating in advance welding and heat treatment after welding together, such a nearly strong weld as the parent metal can be obtained.
A two-dimensional model for solid state bonding process is proposed. The bonding process is assumed to be achieved by four fundamental mechanisms: plastic deformation, creep deformation, interface diffusion and volume diffusion. The numerical analysis based on this model makes it possible to understand quantitatively the effects of temperature, pressure, bonding time, asperity of faying surface on the bonding process. Besides, it is possible to estimate the relative contributions of the four bonding mechanisms to the percent bonded area. It is found from the analysis that the deformation mechanisms tend to be dominant with increasing temperature. The tendency is striking under high pressures.
The two-dimensional model of bonding process proposed in our previous report (Part 1) was experimentally verified, using an oxygen-free copper as material for bonding tests. The boundary conditions in the bonding tests were settled in accordance with the two-dimensional model. The ranges of test conditions (bonding time, pressure and temperature) were determined by the numerical calculations. The experimental results are in good agreement with the calculated results. It is also found that the bonded interface (bond-line) does not migrate during bonding even if the percent bonded area roughly attains to 100%. It is, therefore, considered that the two-dimensional model proposed in Part 1 can be appropriate to actual solid state bonding process.
Charpy impact tests have been carried out on diffusion bonded joints in 2.25Cr-1Mo steel and 13Cr steel, and the effects of surface roughness and annealing treatment (postheat treatment) on charpy impact properties of the joints have been investigated. Impact properties of the joints confined the bonding deformation have been also assessed. The results obtained here are summarized as follows; 1) Decreasing the surface roughness resulted in improvement of the impact properties. Surface roughness appears to be an important factor in diffusion bonding since smooth surfaces brought together will have a larger bonding area than rougher surfaces. 2) Subsequent to diffusion bonding, the annealing treatment could improve the impact properties of the joints in both 2.25Cr-iMo steel and 13Cr steel. 3) The joints that were bonded after the laying surfaces were subjected to high temperature oxidation showed very low impact properties. Oxide films on the faying surfaces prevent diffusion bonding although the oxide films are broken up by the plastic flow at the points of contact along the interface and metal to metal occurs partially. 4) As the degree of the bonding deformation was increased, the impact properties improved because of promoting the diffusion of atone across the interface followed by increasing the metal to metal contact area. 5) In the diffusion bonding with confining the bonding deformation, the impact properties increased with the product of pressure and pressing time. The result suggests that to achieve high impact property, it is necessary to choose an optimum bonding pressure in the diffusion bonding with a given deformation.
Effects of the morphology and composition of nickel-base interlayers on the transient liquid phase diffusion weldability of superalloy Inconel 713C have been investigated by microscopy, electron probe microanalysis and high temperature strength tests of the joints. Proper composition adjustment, powder refinement and homogenization of the interlayers were indicated to be both important for the improvement of the weldability. Especially in amorphous interlayers made by the rapid quenching liquid metal method, the composition homogeneity which contributes to easy homogenization of the joints was fairly improved without segregation of molybdenum and hafnium. Additionally, in case of using amorphous interlayers, the thickness of liquid layer formed at the joint interface during welding was revealed to become thinner compared with the case of using powdered interlayers, so that the isothermal solidification of the liquid phase could occur more rapidly. These phenomena were demonstrated to result in increasing the joint strength, and some of the joints showed 100 percent joint efficiency in stress-rupture tests.
A detailed study was conducted on the microstructure and the high temperature tensile properties of SUS304 stainless steel, Inconel X-750 nickel-base superalloy and 2⋅1/4Cr-1Mo heat resistant steel joint buttbrazed with a gold-nickel filler metal and an amorphous nickel-base filler metal. The high temperature strength of amorphous nickel-base alloy brazed joints was superior to that of gold-nickel alloy ones for all the base metals used, and in particular, the microstructure near brazed interface in nickel-base alloy joints, were indistinguishable from that of the base metal. On the other hand, the structure of SUS304 stainless steel and 2⋅1/4Cr-1Mo steel joints brazed with gold-nickel alloy, revealed inhomogeneity in nickel and gold distributions in filler metal layer, and particularly, a filler metal-base metal interface boundary enriched in nickel as a result of up-hill diffusion from base metal. Although the tensile strength above 400°C of all the joints brazed with the gold-nickel filler metal was inferior to that of base metal, the obtained results suggested that these joints possessed excellent corrosion, erosion and oxidation resistance. Notch toughness test indicated that the joints brazed with the gold-nickel filler metal had higher toughness compared to the joints brazed with the amorphous nickelbase filler metal.
In the present paper, joinability and interfacial metallurgical phenomena in explosive welding are experimentally examined for different combinations of aluminium alloys containing or no magnesium and mild or stainless steels with the purpose of clarifying the reason why aluminium alloys containing magnesium can be hardly joined with steel by explosive welding. The experiments show the following facts. The aluminium alloys are soundly bonded with one another, and remarkable segregation of magnesium is observed inside microvoids within fusion layer produced at a certain weld boundary between Al-Mg alloy and aluminium, from which it is deduced that evaporation and condensation of magneisum occur in the molten alloy overheated during the welding process. The explosive process for flyer plate of Al-Mg alloy and parent plate of mild or stainless steel results in poor or no weld accompanied by formation of fusion layer at the boundaries. The fusion layers between Al-Mg alloy and mild steel have chemical compositions mainly based on the Al-Mg alloy, comparatively high hardness, and a tendency to cause microcracks in them; and at the non-welded interface, too, segregation of magnesium is observed together with the fusion layer.
It is now questionable that the Liquid-Metal-Embrittlement-cracking (LME-cracking) rises in HAZ of welds of steel structure during hot dip galvanizing. Because of preventing the cracking, it is necessary to study the effect of welding factors on the critical stress of steel in molten zinc (σcr). In this report, the tensile tests were carried out in molten zinc by using the welding joint specimen with U notch in HAZ, and σcr for each materials used was investigated. The results are as follows. (1) σcr decreased as the stress concentration (Kt) was large, but it was approximately constant over Kt=3. (2) As the heat input was large, grain size at coarse-grained region was large, maximum vickers hardness in HAZ was lower and σcr increased. (3) σcr was linearly arranged by using maximum vickers hardness in HAZ.
In previous report, the effect of welding factors on the critical stress for LME-cracking of steel was examined. In addition, because of preventing the crack, it is necessary to study the behavior of thermal stress and residual stress during dipping in the molten zinc that cause the crack in steel structure. In this report, the distribution of temperature and thermal stress during dipping simple plate and pipe in the molten zinc were analyzed. The results are as follows. (1) Maximum tensile thermal stress, (σt)max occurred at the lower side of plate and pipe, and caused LME-cracking at this position. (2) (σt)max increased as plate width is large and plate thickness is small. And (σt)max increased as pipe diameter is large. (3) For the plate and pipe, (σt)max increased as dipping velocity is small.
In the second report, thermal stress during dipping the simple plate in the molten zinc was analyzed. And it was indicated that maximum tensile thermal stress, (σt) max occurred at the lower side of plate, and caused LME-cracking at this position. In this report, because of confirming the above crack position, the simulation test specimens for LME-cracking were devised, and were dipped in the molten zinc. The results are as follows. (1) LME-cracking occurred at the lower side of plate, and the results consisted with the results by analysis of thermal stress. (2) The addition of the thermal stress and residual stress affected the initiation of the cracking. (3) To make dipping velocity high, to give dipping direction careful consideration, or to make shot peening is a good example of preventing the crack.
The data base system for an effective use of the SH-CCT diagram for welding (CCT diagram) has been developed by the use of an interactive personal computer. The data base has memorized about 200 sheets of CCT diagrams and data for estimation of hardness and percentage of microstructures. The characteristics of this CCT diagram data base system are as follows: 1) In order to be most effective, this system has following three procedures for the practical application of the data base. i) Procedure I is the case of the estimation of CCT diagram, hardness, and percentage of microstructures for some steel that the user desires to investigate HAZ properties. The CCT diagram with similar composition for that steel is selected from the data base and displayed on a CRT. If there is no suitable CCT diagram in the data base, it is possible to display with overlapping two CCT diagrams of which the amount of one or two elements differ from that steel. The user can estimate the CCT diagram of that steel by the interpolation or extrapolation from overlapped CCT diagrams. ii) Procedure II is the case of the study for the effect of alloying elements on CCT diagrams, hardness, and percentage of microstructures. When the user input the all composition ranges excepting the element under consideration, CCT diagram under the condition is selected from the data base. iii) Procedure III is the case of the steel selection under the condition of the limited welding condition or study of the CCT characteristics. When the user feeds the critical cooling time ranges, CCT diagram corresponding to it is selected from data base. 2) Hardness and percentage of microstructures are estimated and displayed on a CRT, when CCT diagram is selected from the data base and cooling time (A3 to 500°C) is fed or a calculated weld thermal cycle is given. It is considered that this CCT diagram data base system is very effective for the weldability evaluation, the steel selection, and the development of a steel by the use of above functions of the selection and displaying of CCT diagram.
The report is composed of a study of the influence of four factors, oxygen, hydrogen, ferrite content and welding conditions, on the blowholes in the weld metal, using covered arc-welding electrodes for the pitting corrosion resistant austenitic stainless steel with high nitrogen concentration (25Cr-13Ni-1Mo-0.35 N). Compositions of gas in the blowholes of weld metal were also checked. The experimental results were as follows; 1) As the amount of hydrogen in weld metal increases, so does the number of blowholes in a circumstances where oxygen content are high (0.06%). The number of blowholes decreases when oxygen content are lower and the influence of hydrogen for blowholes also decreases. The number of blowholes is very few at 0.04% oxygen and 5 ppm hydrogen. 2) The number of blowholes much fluctuates by welding conditions when both oxygen content (0.06%) and hydrogen content (8 ppm) are high. When oxygen content (0.04%) and hydrogen content (5 ppm) are both lower, the number of blowholes in weld metal decreases and blowhole is almost exempted from the influence of welding conditions. 3) The number of blowholes does not change until ferrite content exceeds 5% but it begins to increase when ferrite content exceeds 50%. 4) Hydrogen and nitrogen gas were found in the blowholes of weld metal with oxygen content 0.06% and hydrogen content at 8 ppm. 5) It can be concluded that prevention of blowhole in stainless steel weld metal with high nitrogen concentration (0.29-0.34%) could be achieved by lowering oxygen content less than 0.04% and hydrogen content at 5 ppm.
The erosion/corrosion damage symptom was experienced in a part of units made of carbon steel in nuclear power plants. The damage was erosion/corrosion one caused by the wet steam stream containing little dissolved oxygen. Therefore, erosion/corrosion tests were executed about various kinds of steel having different additional elements. As the results of the tests, it has been concluded that 11/4Cr-1/2Mo steel has excellent erosion/corrosion resistance. This material was applied to actual plants to solve the above problem for the time being. However, since this 11/4Cr-1/2Mo steel is heat-resisting steel for hot pressure vessels primarily, it contains chromium and molybdenum in addition to about 0.16% of carbon. It is necessary for the prevention of cracking in the welds of this steel to keep preheat and interpass temperature at 200 to 350°C during welding and perform dehydrogen heating process at 400°C for 30 min after completion of welding. These procedure is very much complicated, as compared with the procedure for the welding of carbon steel. Furthermore, the material's strength is not so much important at the elevated temperature higher than 400°C, because the maximum temperature of the steam is 282°C in the units concern. Therefore, the reduction of carbon content has been investigated, for the improvement of the weldability of 11/4Cr-1/2Mo steel. The effect of carbon content has been examined on tensile properties, Charpy absorved energy, the resistance against weld cracking and erosion/corrosion properties. As the results of the investigations, (1) the carbon content can be reduced to 0.07 to 0.10% in case of annealed type of steel, securing its tensile properties and improving weldability, (2) the annealed type of steel can be welded free from cracking without dehydrogen heating process, keeping the interpass temperature more than 225°C, and (3) the hydrogen diffusion parameter τ=Σi(Di/Δti) can be used to prevent multi-pass weld cracking.
In this report the effect of nonmetallic inclusions on weld cold cracking has been investigated. Q-T type HSLA experimental steels having various inclusion contents were employed. These steels had the different sulphur contents ranging between 0.006% and 0.032%. Nonmetallic inclusions were mainly sulphieds and oxides. So inclusion contents were relative to sulphur and oxygen contents. The relationship between cleanliness and the sulphur+oxygen contents were indicated as following equation, d=0.0011 (S+O)+0.054 d: Inclusion area fraction at L-Z plane (%) S+O: Sulphur+oxygen content (ppm) The result of butt joint type implant test showed that lower critical stress decreased with decreasing inclusion contents. It was found that reducing inclusions increased the risk of weld cold cracking. MnS inclusions had no significant effect on hardenability of steels. So the inclusion contents must be evaluated as one of the factors affected cold cracking.
In the previous work, it was obtained that reducing inclusion contents increased the risk of weld cold cracking. In this work, further examination of the effect of nonmetallic inclusions on HAZ hydrogen induced cracking was carried out. The sensitivity of hydrogen induced cracking was evaluated by hydrogen charged three point bending test for synthetic HAZ. The results in this work were as follows: (1) At room temperature, inclusions acted as crack initiation site, so KIC of hydrogen-free synthetic HAZ specimens decreased with increasing inclusion contents. (2) In hydrogen-charged specimens, increasing inclusions result in the elevation of KTH and decrease of crack growth rate. It was aquired that inclusions reduced the sensitivity of HAZ hydrogen embrittlement. (3) It was considered that this effect of inclusions on reducing sensitivity of hydrogen embrittlement was mainly caused by the hydrogen trapping effect of inclusions. (4) Ce treatment had no significant effect on crack initiation and propagation of hydrogen induced cracking.
The cold cracking sensitivity of high strength steel in wet underwater welding was experimentally investigated by means of the implant weldability test with coated electrodes. The experiments were done with HT60 steel plates and D5003 covered electrodes, and the specimen 6 mm in diameter having 1 pitch 40 degree spiral V notch with 0.5 mm depth, and 0.1 mm tip radius. The results are the following: (1) In the implant two pass welding in comparison to single pass welding, the lower critical stress for the cold cracking (σcr)imp increased by about 20 kgf/mm2 to about 55 kgf/mm2 in underwater welding and also by about 20 kgf/mm2 to about 75 kgf/mm2 in air welding: The lower critical stress ((σcr)imp in underwater welding was about 65-75 percentage of that in air welding. (2) By underwater two pass welding the columnar structure of the weld metal was transformed into a globular structure, and the martensitic structure of the heat-affected zone was transformed into the tempered structure. By air two pass welding the needle-like martensitic structure of the heat-affected zone was transformed into a bainite structure which was a fine pearlite. (3) In underwater welding, the micrography of the implant fracture surface showed mainly the quasi-cleavage of hydrogen embrittlement and the intergranular pattern near the notch in case of single pass welding. In air welding, it showed mainly the dimple fracture, and the quasi-cleavage of hydrogen embrittlement at lower stress.
The present study proposes a measurement of transient welding strains in areas near weld. In the measurement technique, grid patterns previously photo-etched on surface of a plate are photographed progressively during welding; after welding, each grid distance at every moment is observed with the photographic film using micro-photometer, from which total strain is determined. Experiments are conducted to examine the accuracy of the measurement and the mechanism of radial and circumferential strains in aluminum alloy thin plate heated by gas tungsten arc. Moreover, the plastically deformed zone in the plate is sized from the two-dimensional total strain values by a mathematical equation based on the theory of elasticity and plasticity. The main results are as follows. The photographic recording method reveals precisely the total strain distribution which shows the individual change according to the plastic deformation occurring around the molten zone and the cooling effect of shielding gas as well as the thermal expansion of the plate. The size of plastic zone calculated from the total strain values after heating is reasonably close to that experimentally observed by stress relaxation. The size spreads at early stage of the heating with additional deformation in the thickness direction and increases with increasing heat input.
In this paper, a mathematical analysis of residual stress is proposed, by which the plastic strain is calculated from an already known total strain distribution without cutting process for relieving the elastic strain. In order to confirm the analysis, numerical calculations are carried out on the following two subjects. First, the differential equation and boundary condition are derived from the condition of compatibility and the equation of equilibrium on the assumption of incompressibility, plane stress state and nonphase transformations. The differential equation is applied to find the plastic strain value in the case that the total strain distribution for an arbitrarily assumed plastic strain distribution has been known by the analyses of inherent strain method. The resultant values of the plastic strain are in well agreement with the assumed ones. Second, the equation is applied to analyze the residual stress and distortion resulting from spot heating of aluminum alloy thin plate. The results coincide with the experimental data except around the heating point where swelling deformation occurs and the stress state is three dimensional.
To investigate effects of the corrosive environments on the fatigue strength of spot welded joint, the fatigue strength of spot welded joint which have suffered from corrosion under the outdoor exposure is first investigated. Next, in order to investigate effects of the corrosion caused by highway de-icing salt on the fatigue strength of spot welded joints in some countries, the fatigue tests of spot welded joints in the salt water spray and the salt water dipping are carried out. For the purpose of comparison, moreover, the fatigue test of spot welded joints in the pure water dipping for some test specimens are also intended to try. Test specimens used are of mild steel (SPCC) in most experiments and 440 MPa- and 780 MPa-classes high strength steels in a few experiments, which thicknesses are all 0.8 mm. As the results, unignorable decrease of the fatigue strengths of spot welded joints in each case is found. Moreover, in the experiments under the outdoor exposure and the salt water spray, it is proved that sheet separation of spot welded specimen plays an important role in the decrease of these fatigue strengths.
In the authors' previous report, although effect of residual stress on fatigue crack growth rate was quite significant, that of microstructure of the weld metal was also found to he significant: The growth rate of a weld metal specimen was higher than that of a base metal when the growth rate was plotted against effective stress intensity range. In the present study, metallurgical factors accelerating fatigue crack growth rate of weld metal specimens have been investigated. Effects of inclusions and delta ferrite are seemed to be negligible in the present range of the crack growth rate. Although effect of crystallographical heterogeneity is found to be significant, the heterogeneity may not be the factor that the fatigue crack growth rate of a weld metal specimen is higher than that of a base metal. The main factor is considered to be that dendrite structure of the weld metal is too coarse to easily cause martensitic transformation.
SCC susceptibility of sensitized SUS 304 stainless steel in high temperature water was studied. The results are as follows. SCC susceptibility was increased by adding crevice to tensile specimen surface, for the corrodent being to acidify by hydrolysis in crevice. SCC susceptibility was best fit to TTS curve gained by EPR test than other corrosion tests such as Strauss test and grain boundary corrosion test in high temperature water. In addition, giving synthetic weld thermal cycle before the sensitizing heat treatment, the sensitization was considerably promoted. This would be caused that nucleation of carbide was occurred in synthetic weld thermal cycle process and the carbide growth and chromium depleted zone formation around the carbide were promoted in following sensitization process.
The methods of plasma jet noise suppression for plasma metallizing are described. In this study the new muffler of reactance type which have the functions of noise suppression and plasma jet atmosphere control has been developed. Examining the effects of muffler under the various conditions, it has indicated that the value of noise attenuation is obtained from 12 to 21 dB, and the gas concentration and temperature of plasma jet are kept at the good conditions for plasma metallizing.