A reliable method of weld-line detection for electron beam welding has been developed by incorporating semiconductor X-ray sensor and signal processor. The fundamental characteristics of weld-line detection and the signal processing to eliminate the noise component are studied. The sensing methods of X-ray and scattered electrons are compared under the condition of practical use. The conclusion obtained are summarized as follows: (1) The X-ray sensing method is very reliable, comparing with the scattered electron method, because of its durability against metal vapours and sputters, and its complete shielding property against an electromagnetic noise. (2) The processing of the weld-line signal, such as a time averaging, is very effective for high resolving power, because the weld-line detector is used in the environment of high noise level caused by high-frequency inverters, power contactors, and so forth.
Adhesion strength of sprayed coating, F, is related to fused metal temperature in arc spraying of aluminium and stainless steel. Fused metal tempreatures are estimated at tow stages on the flight process of fused metal. One of them, Tc, is estimated at adhesion stage with a silicone oil calorimeter, and the other, Ti, at fusion stage by the calculation of heat input. Main results of the study are summarized as follow; (1) F, Tc and Ti depend on the wire feed speed parameters ν+/(ν++ν-) where ν+ is positive electrode side and ν- is negative. The graphs of F, Tc and Ti versus ν+/(ν++ν-) all exhibit a similar pattern. (2) F increases with increasing Tc and Ti. (3) The maximum F is obtained when heat input per unit wire deposition is maximum. (4) The arc spraying condition to obtain the maximum F is estimated by measurement of the heat input parameter [S.S.H.], where [S.S.H.] is calculated from ν+, ν- and average arc current.
As Laser beam can be focused to pointed area, it is suitable to apply high speed welding of thin sheet metal. This experiment was carried out to know what advantage can be expected by applying Laser beam welding to surface coated steel sheet and austenitic stainless steel. The results obtained in this report are as follows; 1) Steel sheet can be welded with much smaller distortion by Laser beam welding, compared with TIG welding. For coated sheet, Laser beam welding gives less damage to coated layer than that of TIG weld-ing. It is possible to make full penetration weld to use 3-5 times faster speed by Laser beam welding than by TIG welding. 2) TIG weld metal of Zn coated sheet shows Zn rich region at surface but Laser weld metal does not. 3) Laser beam welded joints of stainless steel show little weld decay tendency, which is almost same level as electron beam welded joint.
It is well known that fatigue crack propergates accompanying a small scale yielding at the crack tip. In filler metal between base metals of brazed joint, fatigue crack growth rate depends possively on the degree of restraint of crack tip plastic deformation by base metals, because the width of crack tip plastic deformation zone is nearly the same with the width of joint gap and crack tip plastic deformation can be restrained by base metals. The theoretical discussions on correlation of crack tip plastic deformation and base metals revealed; 1) The degree of restraint of crack tip plastic deformation by base metals depends on yield strength of filler metal in joint gap, stress intencity factor and joint gap. 2) Under shear stress, crack tip deformation is restrained when joint gap is smaller than a certain scale, and fatigue life of joint becomes longer. 3) Under tensile stress, base metals do not restrain a crack tip plastic deformation, and fatigue crack growth rate depends on stress concentration factor range which becomes greater with the width of joint gap. Some experiments on fatigue crack propergation rate in copper filler metal of steel butt joint showed good agreement with the theoretical assumptions.
Fatigue strength characteristics at room temperature were investigated for the base metal and electron beam welded joints of SGV49 steel. In load-controlled high cycle fatigue tests, the effects of reinforcement and stress relieved annealing were compared. In strain-controlled low cycle fatigue tests, on the other hand, fatigue strength between the base metal and welded jioint without reinforcement were compared. The results are suzmnarized as follows: (1)The high cycle and low cycle fatigue strength cbaracteristics were made clear for the electron beam welded joints of SGV49 steel. (2)The fatigue strength of the electron beam welded joints in the high cycle region is higher than those of the schielded arc welded joints and submerged arc welded ones. (3)The high cycle fatigue strength is improved due to the stress relieved annealing which has an effect to reduce the residual stress of welded joint. (4)All the fatigue cracks in the welded joints without reinforcement are observed at the base metal, because strain concentration in the base metal were occurred due to the different material characteristics of the base metal and weld metal. In the low cycle region, moreover, the fatigue curve for the base metal agrees well with that for welded joint using strain concentration factors.
In order to get the fundamental knowledge about the pitting corrosion in austenitic stainless steel welds, some experiments with TIG welds of nine kinds of steels were conducted. The pitting phenomenon occurring in ferric chloride solution was observed minutely, and the localized corrosion potential distribution at the weld was measured to. explain the location where the pitting corrosion is apt to occur. The following results were obtained: There were three types of forms in a weight loss of austenitic stainless steel welds by pitting corrosion in ferric chloride solution. When a delta ferrite phase appeared in weld metals, the pitting corrosion concentrated on the weld metal, and this resulted in a large weight loss. The measurement of the localized corrosion potential distribution revealed that the locations which were likely to be anodic were a slaglike oxide-carbide deposited on the weld metal surface, the interface between the slaglike oxide-carbide and a matrix, and the ripple lines on the weld metal surface.
Measuring corrosion potential at the micro-part of the weld metal surface of many kinds of austenitic stainless steels has revealed that the ripple lines formed on the weld metal surface are apt to be anodic and be corroded by pitting. In this study, the reason why the pitting corrosion is likely to occur at the ripple lines and the phenomonon of pit-growing in a weld metal interior were discussed metallographically. The following results were obtained: The ripple lines on the weld metal surface correspond to the bandlike regions where delta ferrite phases exist high densely. The delta ferrite phase at the ripple line supplies a site for the pitting corrosion to start, and promotes the pit progression. The mechanism for solute segregation to occur at the ripple lines was explained qualitatively from solidification metallurgy.
Though it is often necessary to perform repair welding in structures already constructed, welding under pulsating stress or oscillation is considered to be undesirable for operative weldability and crack sensitivity. In this study, welding crack test was carried out for HT-60 to survey the possibility of welding under pulsaring stress in bridges, offshore structures and power transmission lowers, etc. The results obtained are as follows: 1) Tne crakes detected in welded joint under pulsating, stress are classified into solidification crack and root hot crack in weld metal. 2) The solidification crack arises under high stress frequency and high stress range. 3) The critical stress range for root hot crack is smaller than that for solidification crack, and it decreases under decrease of stress frequency and increase of heat input. 4) It was clarified that the welding under pulsating stress is possible when the restrain intensity of weld joint, stress range, groove length and stress frequency is known.
A production technique of Ultra-fine Particles (UFP) has been investiagted to achieve a high genera tion rate of UFP. Ultra-fine Ni, Fe and Ti particles were generated in the Hydrogen-Argon mixed gas atmosphere at various current between Tungsten electrode and the bulk metal, and the generationrate of the UFP were measured. It is found that the shape of arc is changed by increasing the arc current abruptly and the generation rate of UFP is drastically reduced at the particular arc curret (transiticn current). At the lower arc current than the transition current the arc is concentrated on the anode spot, and the generation rate of UFP is very high. At the higher arc current than the transition current, the arc spreads on the bulk metal, and the genreation rate is very small. This transition current changes, depending on a concentration of hydrogen in atmcspher, arc length and a kind of bulk metal.
From the viewpoint of fundamentally examining the weld metal solidification process by referring to knowledges of casting to prevent the high speed SAW solidification defect, investigations were previously made on the relationship between the solidification variables in weld pool and the solidified microstructures using 25Cr-20Ni austenitic steels (Reports Nos. 1 and 2). In the present report, solute behaviours during weld metal solidification have been discussed. In the weld pool quickly solidifying close to a high-temperature heat source, a violent liquid flow occurs. This is a large difference between welding and casting. In the previous examination, however, it was shown that the formation mechanisms of solidified microstructures for both welding and casting are identical owing to a great thermal influence, in spite of their difference in liquid flow condition. On the other hand, the influence of liquid flow was clearly revealed on the solute behaviours such as micro- and macro-segregation. The present report has quantitatively pointed out the features of such behaviours. Moreover, the micro-segregation results have been applied to Burton's analytical solution concerning the degree of liquid-phase mixing to estimate the flow actions at various parts of SAW weld pool.
Fracture toughness testing of heat-affected zone, especially grain coarsened zone, in welds is considerably difficult compared with weld metal and base metal, because the embrittlement of HAZ causes in the localized region. However, grain coarsened HAZZ is usually the most embrittled region in welds, it is often required to evaluate fracture toughness of its region itself. In the present paper, a probabilistic procedure for evaluating fracture toughness of the localized embrittlement region has been proposed newly, based on the weakest link model. By means of this procedure, distribution of cleavage toughness of localizedt embrittlement region, e.g. grain coarsened HAZ, is proved to be analyzed from test results on specimens of which notch is located in weld metal and base metal, respectively, and cross-bond-type notched specimens which have localized embrittlement region at notch front. Moreover, the sufficient number of cross-bond-type notched specimens which are necessary to evaluate fracture toughness of localized embrittlement region itself according to our present procedure has been investigated. By using 20 or more cross-bond-type notched specimens, cleavage toughness of the localized embrittlement region can be grasped.
Small crack-initiation-arrest events so called Pop-ins often occur at COD tests for welds and COD values at such Pop-ins are usually very small in comparison with those at. the following final fractures. Present assessment regards Pop-in as a critical event because significance of Pop-ins for actual structures hasn't been made clear. Therefore much effort has been made in materials and welding procedures in order to prevent Pop-ins. It is, however, considered to be too conservative to assess Pop-in as initiation of critical brittle fracture if it.is proved that Pop-in makes no influence on the safety of actual structures. And so it is indispensable to clarify the significance of Pop-ins which occur at COD tests and to establish their safety assessment in actual structures.
The purpose of the present study is to conduct the consideration on V-notch Charpy characteristics of HT80 electron beam welds which have remarkable hcterogeneity, by using side-groove Charpy tests developed in this study. Two kinds of 800 MPa class high tensile steels were used and three kinds of heatinput conditions of electron beam welding were selected. Both standard V-notch Charpy specimen and Charpy specimen with deep-both-side groove, 3 mm deep, were used. The fracture path of electron beam welds which have considerable heterogeneity does not necessarily select the net section of standard V-notch Charpy specmien. For that case, the evaluation method proposed newly in the present paper is effective to evaluate fracture transition temperature vTS of weld metal/HAZ of EB-welds. The absorbed energy vE versus temperature T relations of welds should be arranged uniquely by using the relative-temperature parameter (T-vTS). Although the evaluation of absorbed energy of HT80 EB-welds by standard V-notch Charpy tests is impassible due to remarkable heterogeneity in strength, the evaluation method using side groove Charily tests and the absorbed energy vE versus (T-vTS) curve proposed newly gives the reasonable results from the engineering sense.
As a basic research of diffusion bonding between dissimilar materials which have the marked difference in coefficients of thermal expansion, diffusion bonding of WC-Co hardmetal to steel has been carried out. Thermal stresses generated as a result of the difference in the coefficients of thermal expansion of the hardmetal and the steel during the cooling of bonded parts have been estimated by. the theory of thermal elastic analysis based on the finite element method. Tensile strengths of the bonded joints have been also discussed on the effects of thermal stress, interlayer thickness and cooling rate after bonding. It is found from the result of the calculation that a maximum tensile stress is generated on the surface of the bonded hardmetal. Therefore, the bonding strength seems to be lowered by the thermal stress. The use of an interlayer affected the bonding strength. The bonding strength increased through a maximum at 0.25 mm thickness of the interlayer then decreased with increasing the thickness. The improvement of the bonding strength is due to the decrease of the thermal stress. The bonding strengths were improved at faster cooling rates than 13°C/min. The improvement of the bonding strength was interpreted by the decrease of the thermal stress whihc is due to the expansion of the bonded steel caused as the result of the martensite transformation during cooling.
As a series of the development for the welding simulator, the authors proposed the system with which any user can compute easily the thermal conduction. If shapes of an object and a preheating region can be drawn on a CRT graphic display, computing the thermal conduction of the drawn object is executed automatically. This system can be applied in the following cases; (1) two-dimensional heat conduction in a finite object (2) a three-dimensional heat conduction in a finite object with a uniform cross section to the welding direction-The uniform cross section is drawn on the CRT, and a size and heating range to the welding direction are put with the numerical value. (3) a special case of two dimensional heat conduction in several thin plate structures as a box or vessel-The development of the structure is drawn on the CRT. In the case of (1), (2), and (3), a thermal conduction is processed by a use of the finite difference method. (4) a large size plate or a long pipe-A shape of the heating region is drawn on the CRT. Point or line heat sources are distributed in the drawn shape, and the heat conduction is processed by the summation of the analytic solution
Aluminum alloys and stainless steels are used in the construction of many types of industrial equipment, but the welds in these materials are subject to micro-cracking and blowholes. In order to reduce such welding defects, the authors used magnetic stirring in TIG welding of an Al-Mg-Mn alloy (5083) and SUS316, and studied the effects of magnetic field intensity and frequency and welding conditions on the solidification structures, hot cracking and blowholes in the welds. The test results are summarized as follows: 1) When aluminum alloys had a field intensity between 100 and 300 gausses and field frequency between 5 and 10 Hz and stainless steels had field intensity between 200 and 300 gausses and field frequency between 1 and 5 Hz, the magnetic stirring reduces the grain size. The combined effects using the pulse arc were also observed. 2) Under the conditions in 1), the columnar structure disappeared. This contributed to the reduction of hot cracking. 3) The magnetic stirring released gas from the molten metal, and as a result, reduced the occurrence of blowholes.
The applicability of 100 kgf/mm2 grade high tensile strength steel developed for penstock was evaluated in this paper. Firstly, five kinds of weld-cracking tests were performed and it was demonstrated that the 100 kgf/mm2 grade steel, including its weld metal, has a good resistance for cold cracking. Secondly, mechanical properties and fracture toughness were investigated and evaluated the safety of the weldment against brittle fracture. As a result, it is confirmed that the 100 kgf/mm2 grade steel weldment has enough toughness to prevent the brittle fracture. Finally, the corelation between fracture toughness and absorbed energy obtained by Charpy-V test was investigated, and Charpy-V values required to prevent the brittle fracture was proposed.
In an earlier report an initial investigation into the influence of parent plate steel deoxidation practice, and in particular Al level, on the microstructure and toughness of submerged-arc welds had shown that even small changes in weld metal Si and Al levels (e.g. 0.02 to 0.03% Al) could produce drastic deterioration in Charpy toughness when using some basic fluxes. In the present report the results are presented of further work, primarily aimed at improving the tolerance to high weld metal Al levels, by using TiO2 additions to fluxes or Ti additions to wires. Significant improvements in toughness of high Al (0.03-0.04%) weld metals were observed by increasing flux TiO2 contents and weld metal oxygen levels. Titanium introduced from the wire was much less effective than that introduced from TiO2 in the flux. A schematic diagram describing the different effects of Al, Ti, Si, oxygen and flux TiO2 content on acicular ferrite formation is proposed.
The diffusion bonding has been applied to the dissimilar metal joining of aluminum bronze (JIS C-6191) to austenitic stainless steel (JIS SUS 316L) which is very difficult to bond by conventional welding techniques. The microstructure of the bond zone and fractured surface of the joints have been examined to get better understanding of important factors that determine the strength of the joints. Results obtained are summarized as follows. In the diffusion bonding without insert-metal the maximum tensile strength of the joint, which was obtained at the bonding temperature of 1273K, was about 300MPa much lower than the strength of base metals. In this joint the stainless steel adjacent to the bonding interface undertook transformation from austenite to ferrite owing to the increase in the concentration of aluminum (ferrite former element) supplied from aluminum bronze. Along the grain boundaries in the transformed layer, an intermetallic compound composed of Al, Cu and Ni was observed. When the joint bonded at 1273K was subjected to a tensile test, crack propagated chiefly along the intermetallic compound. Therefore, the intermetallic compound was considered to be an important factor that depressed the strength of the joint. In order to improve the strength of the joints, copper foil and iron foil as the insert-metal were used. The formation of the intermetallic compound was suppressed considerably by using the insert-metal. However, when iron insert-metal was applied, it was very difficult to attain intimate contact between stainless steel and the insert-metal, because the flow stress of the insert-metal was much higher than that of aluminum bronze at bonding temperatures adopted. On the other hand, when copper insert-metal was applied. The tensile strength of the joint was considerably increased compared with that of the joint without insert-metal. The maximum tensile strength of 400MPa was obtained at the bonding temperature of 1313 K by using the copper insert-metal 50 μm thick.
A study of diffusion bonding of Ti-6AI-4V alloy has been made to lower the bonding temperature and pressure. Al brazing sheet, whihc is consist of 0.6 mm thickness A3003 core material and 0.07 mm thickness Al-10% Si clad metal on both sides, was used as an intrelayer and the bonding parameters, temperature, pressure and time, were changed in different conditions. Al brazing sheet has been also compared with pure Al interlayer in bonding strength in order to make clear the effect of Al-1OSi clad metal in the Ti alloy bonding. The bonding strength increased with incraesing bonding temperature, pressure and time. The joint bonded at 610°C for 30 min with a pressure of 0.5 kgf/mm2 showed tensile strength of 20 kgf/mm2. The diffusion bonding of the Ti alloy with an interlayer of Al resulted in the formation of intermetallic compounds at the bond interface, especially the bonding with an interlayer of Al brazing sheet showed the excessive intermetallic formation. However, the bonding strength increased as the thickness of the intermetallic compounds was increased from 2 to 7 μm. The significant difference between Al brazing sheet and pure Al interlayer was recognized in the strength of joints bonded with the pressure of less than 0.2 kgf/mm2 and for the time of less than 15 min. The bonding strength of the joint with Al brazing sheet interlayer ieacl ed 12.5 kgf/mm2 with no bonding pressure although in the bonding with pure Al interlayer the strength was not achieved. Improvement of the bonding strength by the use of Al brazing sheet interlayer was attributed io melting of Al-Si clad metal which leads to increase of the contact area and acceleration of diffusional processes at the bond interface.
The surface film of weld parts is a very important factor affecting the weld characteristics of diffusion welds. It is desirable to clarify the behavior of the surface film on the diffusion welded interface. In this study, the surfaces before and after diffusion welding were observed with Auger electron spectroscopy. Composition and thickness of the welding surface, and the relation between change of surface composition by diffusion welding and tensile strength of welded joints are investigated. The following results were obtained. 1) The films of the welding surface of aluminum, copper, iron and SUS 304 stainless steel are composed of oxygen, carbon and base metal. 2) Composition and thickness of the surface films of various materials do not so much depend on the surface treatment such as the degreasing with acetone and the annealing in a vacuum. 3) The surface film along the welded interface of aluminum does not change during diffusion welding, but those of copper, iron and SUS 304 stainless steel disappear. 4) When the surface film disappears during diffusion welding, metallic bonding is formed at intimate contact area along the welded interface. The stability of the surface film has an influence on tensile strength of welded joints. 5) The segregation of sulfur is observed on no-contact surface along the welded interfaces of copper, iron and SUS 304 stainless steel, but it does not have much effect on tensile strength of welded joints.
A method by which intensity distribution profiles of focussed CO2 laser beam are determined from the shape of evaporated groove in acrylic plastic, polymethyl-methacrylate (PMMA), scanned across the beam has been developed. This is based on the fact that acrylic plastic is sublimated by focussed laser beam with negligible thermal conduction loss. In this paper, two essential thermal constants are determined; energy for evaporation H=3000 J/cm3, and threshold energy of evaporation G=6 J/cm2. An equation is derived which correlates the beam intensity distribution curve to shape of the groove cross-section in PMMA scanned across the beam. An accurate intensity distribution has been experimentally shown to be obtained up to power density, at least, 1055W/cm2 unless the scanning speed v is smaller than a critical value given by vmin=2W/√πa(2aH+G), where 2a is 1/e-diameter of the beam, and W laser power.
Melting characteristics of mild steel, stainless steel and copper alloy wires, are investigated for pulsed or constant current MIG arc using transistor controlled power supply. Results obtained are summarized as follows; (1) Wire melting rate in MIG welding is affected by many factors; effective anode melting potential, length and resistance of the electrode wire extension, heat contents of metal droplets and electric current applied. (2) Wire melting rate in pulsed MIG welding is found to be independent of pulse frequency, and is expressed as a function of average value and effective value of pulsive current applied. Even if the average current is kept constant, melting rate of electrode wire is possible to increase as the effective value of pulsed current becomes higher. (3) Heat conteut of metal droplets depends on an anode heating of MIG arc and joule's heating in a segment of the electrode wire travelling from the contact tip to the arc.
A measuring method for triaxial residual stress distributions that are axisymmetrical but not uniform both in radial and in thickness (namely axial) directions, was proposed and the accuracy of the measurements was confirmed. This method needs thin arch-specimens, of their length about three times as the thickness of a joint to be concerned, and a thin r-specimen, with their long axes along circumferential and radial directions, respectively, to be cut loose from the joint. The residual stresses of the joint are estimated both from the strain changes induced in the long axis of each thin plate when it is cut out, that is the strain change in the eircumferential direction for the arch-specimen Δεθ and the radial strain change for the r-specimen Δεγ and from the stresses left in those thin plates, in which the stresses are in the plane stress state. The first approximation for the residual stresses is obtained by assuming that the Δεθ and Δεγ are linear across the thickness of the plate and that the relieved stress in the thickness direction in the r-specimen when it is cut out, that is σ'z, is neglected. Then, the distribution both in the radial and thickness directions of this first approximated circumferential residual stress σθ, in other words the stress distribution acting on the section of the r-specimen before its cutting, can make it possible for the distribution in the thickness direction of Δεγ and σ'z to be calculated by finite element method and results in the more accurate estimation of the residual stresses. This second approximation is almost attainable limit by this proposed method and depends strongly upon the discrepancy of the Δεθ from a straight line joining the measurements both at top and bottom surfaces of the arch-specimen. This nature of nonlinearity concerning Δεθ becomes stronger as the weld diameter of the joint decreases. The accuracy for the residual stresses, however, maybe maintained good enough even in the weld diameter being 300 mm.