Investigations were made on the depth profiles of nitrogen (N) and oxygen (O) absorbed in HAZ of ZrTN802D alloy (Zircaloy-2) tubes relative to the microstructure changes by TIG welding in the atmospheres with extremely low level of N2 and O2 partial pressures in total pressures of 0.10 and 0.32 MPa. The original fine microstructures of cold worked and heat treated ZrTN802D alloy tubes were changed by transformation in the HAZ heated to α+β and β phase temperature ranges (1, 090-2, 113 K), and the regions microstructurally changed by welding at 0.32 MPa were narrower than those welded at 0.10 MPa. By the measuring of secondary ion intensities of 90Zr14N- and 18O- using SIMS continuously from surface into deeper portion in HAZ, it was made clear that N was absorbed and diffused at the portion heated to α+β and β phase temperature ranges therein and the content of N decreased exponentially toward inside. O was absorbed more at the portion heated within a phase temperature range (<1, 090 K) in HAZ rather than that of β phase range in HAZ and O was diffused thereinto within only a few μm in depth.
High toughness are requested in the weld metals for offshore steel structures and steel line-pipes used at low ambient temperatures. Micro-alloying of titanium and boron effectively improves the toughness of low-alloyed weld metals with tensile strength ranging between 490 and 590 N/mm2. It is well known that refined intragranular ferrite or acicular ferrite nucleates on titanium containing oxides. However, there have been few reports on the chemical composition at local positions of these effective inclusions and their crystal structures. Two types of submerged arc weld metals were used ; one is a silicon-and-manganese type weld metal with a ferrite with aligned second phase and the other is a titanium type one with the acicular ferrite. The mechanical and metallurgical examination included the microscopic observation, Charpy impact tests of the welds and the characterization of oxides in weld metals with X-ray diffractions and analytical electron microscope. The following facts were clarified from the above investigations. The oxides in the titanium bearing weld metal are crystallized in a form of (Mn, Ti) (Al, Ti)2O4 with angularly rugged surfaces, while the oxides of a Si-Mn type are amorphous with smooth spherical shape. Titanium as low as 0.005 wt% in a weld metal satisfactorily crystallized oxides if titanium is included in oxides with aluminum and manganese.
Strength mis-matching between the base and weld metals exerts a marked influence on the deformation behavior as well as on the fracture resistance of the weld HAZ. HAZ-notched CTOD test results for high strength steel welds were discussed with attention to mis-matching effect. Stress fields in the HAZ were addressed by 3D FEM with a model having a notch at the HAZ/weld metal boundary. Strength overmatching of the weld metal brings about different effects depending on the toughness level of the HAZ. In the case of the HAZ with moderate toughness, strength overmatching results in crack path deviation toward a softer material due to asymmetrical plastic deformation. On the other hand, for the embrittled HAZ, the overmatch condition lowers the critical CTOD value of the HAZ. This is attributed to elevation of the local stress in the HAZ by constraint effect of the overmatched weld metal. The geometry of the test specimen also affects the degree of crack tip constraint. The deep notch bend specimen produces the largest geometrical constraint. The fracture resistance of the weld HAZ is controlled by the combined effects of strength mis-matching and the specimen geometry. The geometrical constraint in the deep notch bend specimen was more significant than the constraint by 25% strength overmatching in the tension specimen.
Brazing of A7003 AI-Zn-Mg alloy is considered to be difficult because of its low melting temperature and high content of oxidation susceptible elements such as Mg and Zn. Obtaining high joint strength by vacuum brazing with conventional fillers, where no flux in used, is practically impossible. In this study, Al-Ge-Si-Mg-Cu and Al-Ge-Si-Mg alloys were examined as brazing fillers for A7003 alloy. These fillers were formed into 100 μm thick foils by PFC (Planer Flow Casting) method and used in the brazing experiment to investigate relation between brazing temperature and joint strength. SEM observation of the brazed interfaces and surface analysis of the specimens were performed. In Al-Ge-Si-Cu-Mg fillers, the joint strength values measured by tensile test dispersed widely, whereas average strength was 310 MPa, which is 78% of A7003 alloy's tensile strength. In Al-Ge-Si-Mg fillers, the joints brazed with the filler of 753 K melting temperature showed 340 MPa of joint strength in average with narrower dispersion. Auger electron spectroscopy (AES) carried out on the surfaces of specimens revealed the following facts ; (1) Before brazing, surface of the alloy is covered with aluminum oxide. (2) After the brazing at 773 K, aluminum oxide converts to magnesium oxide partially. (3) Surface oxide changes to magnesium oxide perfectly after the heating at 823 K. Mg in the fillers therefore acts as wetting agent only in the conditions where the brazing temperature is lower than 773 K, being ineffective at 823 k. This is responsible for the higher strength with narrower dispersion in the joint brazed with the Al-Ge-Si-Mg filler of 753 K of melting temperature.
Waste treatment by thermal plasma is an attractive technology from the viewpoint of environmen-tal problems. For this application, the short lifetime of plasma generator (torch) is the most serious problem. It is essentially governed by the durability of electrode, which is used in the severe condition of a rather high current for a long time. In this study, the consumption of tungsten electrode under a high current condition was studied. The consumption test was carried out under the following conditions. For 2.4 mmφ electrode a 350 A, Ar arc was applied for an hour and also for 3.2 mmφ electrode a 500 A, Ar arc was applied. After the test, the weight change was measured, and the morphology was observed by SEM and analyzed by EDX. Tip shape effect was also discussed from the viewpoint of current density. At high current conditions, the tungsten electrode activated by 2% rare-earth-metal oxide (La2O3, Y203, Ce2O3) showed severe consumption. In those cases, rare-earth-metal oxide disappeared near the tip and sometimes vacant holes were formed at the area. The effects of grain morphology on the cosumption were studied. The electrode of longitudinalgrain micro-structure showed better property than that of granular one. This may indicate that migration of oxide is important factor to the consumption of electrode.
A comparative study has been made of characteristics of gas-tungsten-arc (GTA) cathode consisting of tungsten mixed with a small quantity of lanthanum-, yttrium-, thorium-oxide and lanthanum hexa-boride. In this study, temperature distributions of each electrode are compared at various conditions. The temperature distribution was measured by the use of infrared thermal monitor. The influence of arc light emission on the measurement was discussed, and there was a little influence in measured temperature. It was less than 5% of its value. The consumption test of the electrode was carried out at constant current for 1 to 5 hours. After test, the weight change was measured, and the microstructure was observed by SEM and analyzed by EDX. In this study, the LaB6-W electrode showed good performance in high current condition. The temperature distribution of LaB6-W electrode was different from conventional La2O3(2%)-W elec-trode. LaB6(0.2%) -W electrode showed relative flat temperature distribution and La2O3(2%) -W showed steep one. The relation between temperature distribution and consumption of electrode was discussed.
The joining between stainless steel (SUS304) and carbon steel (SS400) was carried out using thermal spray coating of nickel based self-fluxing alloy under atmospheric conditions for basic data. The size of joining specimen is 50 mm in length and 10 mm in diameter. After the each edged surface of SUS304 and SS400 specimens were blasted by used steel grid material sized No. 70, those were sprayed with self-fluxing alloy (S.F.A.) at the each surface of both specimens coated about 100μm in thickness. The effects of joining conditions on the structure and strength of joining were studied. The results are summarized as follows: (1) The maximum tensile strength at the joint part using R notch specimen was about 579 MPa under condition of 30 sec raising time and 60 sec holding time at 1373 K temperature. (2) The hardness gradient was not observed near the joining zone in the Vickers hardness distribution of the both materials. Furthermore, the Vickers hardness distribution near the joining zone of SUS304 was about Hv120, that was lower than base metal because of the annealing effect. (3) The microstructure near the joining zone did not indicate the martensitic structure, the carburized and the decarburized layer because of its lower cooling rate. The structure near the joining zone of SUS304 was indicated in the annealed twin at the transgranular. (4) By the EPMA line analysis across the joining zone, Cr, Ni, and B were not observed because the inserted material S.F.A. was very little diffused and the most of it was discharged out of the joining part. The elementary analysis of Fe was indicated sligthly concentrated gradient.
Evaporation characteristics in CO2 laser welding stainless steel was experimentally analyzed at power densities in a range from 5×104 to 107 W/cm2 with M2 of 1.4 and 5.6. Welding mode transits from a thermal conduction to a deep penetration type at a critical power density around 4-5×105 W/cm2. The penetration depth tends to increase with decreasing M2 with accompanying decreased evaporation loss when the power density at the work surface is the same. The latent heat of evaporation is negligible small, at most around 1% of laser power. In the thermal conduction welding, where the power density is less than 4-5×105 W/cm2, the evaporation rate per unit area was found to be equivalent to that of the deep penetration welding, indicating that the recoil force of the evaporation is at least as high as that of the keyhole welding, providing a shallow hemispherical depression by the recoil force in the molten pool. The evaporation rate in the deep penetration welding decreases with increasing aspect ratio of the weld bead due to the condensation of the vapor at the side wall of the keyhole.
Crimping mechanism between the stranded copper wires and brass terminals was investigated in terms of repulsion force acting on crimp terminations by way of the stranded wires. The repulsion force was estimated from the load-displacement curves recorded during the crimping process. We obtained the results as follows; (1) Repulsion forces, which were based on the elastic deformation of the strand composing wires, are observed between the stranded wires and crimp terminals. (2) The repulsion forces have a peak value at the compression ratio of 27% in the crimp terminations. (3) The suitable conditions of the contact resistance and the crimping strength are secured under the conditions of the peak value of the repulsion forces.
This paper describes the shape processing approach to the schedule problem. Many methods are proposed for the schedule problem until now. However, it is very difficult to apply these methods to solve or optimize the problem, if its condition is changed widely or during the course of processing. The method proposed here increases the flexibility using shape processing. The system utilizes the Coded Boundary Representation (CBR) method which was developed as the geometric model. The CBR method has several features. For example, the model can be represented in the form of lists, and topological features can be easily extracted. It is believed to provide a very useful tool for solving the schedule problem.
The development of a scheduling system which used the geometric model was described and its processing alogorithm was shown in the previous paper. The system utilizes the Coded Boundary Representation (CBR) method which has been developed as the geometric model. The scheduling problem is reduced to a 2 dimensional box-packing problem by using this geometric model. In this paper, the proposed method is applied to the simple scheduling problems which can be processed by ordinary methods. The comparison is made on the scheduling ability of this method with ordinary methods, i.e., PERT and the load balancing method. The proposed method is also applied successfully to the other problem which ordinary methods can not treat with ease. It is shown that this method is very useful and flexible for the general and special problem as the result.
On using the signal processing ability of Backpropagation Model of Neural Network, the noise elimination is performed on the image of a joint part of arc welding. The object image, which is obtained by the slit light slice method, is often used for the detection of joint configurationis on the purpose of welding automation. The noise caused by the welding arc is superimposed on the image and disturbs the detection. Such noise is eliminated through the learning process of Neural Network which is carried out for the noise imposed input images and the noiseless teacher images. The structure of the network, the image input method, the selection of the teacher image and the method to recover the resolution of the processed result are investigated experimentally. It is shown that the noise elimination is successfully done as the result.
The creep rupture strength (CRS) of welded joints of 9Cr-1Mo-V-Nb-N steel was studied by means of welding heat cycle simulation. The reduction of CRS in the welded joints has been successfully reproduced, and the reasons for the reduction was discussed from the points of fine precipitates in the matrix. The CRS of simulated HAZ (Heat-Affected Zone) changes with the peak temperature of welding heat cycle simulation (PT). It goes down sharply beyond Ac1 temperature, then gradually reaches to the bottom at Ac3 temperature of 925°C. At higher temperatures than Ac3, it goes up steadily and shows almost the same CRS as base metal at 1100°C. The weakest CRS of simulated HAZ lies just at the lowest limit of CRS data band of various welded joints prepared by GTAW, SMAW and SAW with the same base material. The simulated HAZ is useful for evaluating and analysing the reduction of CRS in the welded joints. Heating up to Ac3 temperature by welding changes the shape of VN from thin plate to sphere. This makes the size of VN smaller. Moreover, the Ac3 temperature being too low for the solution of Nb, VN that precipitaes further during PWHT (Post-Weld Heat Treatment) contains little amount of Nb ; It causes the contraction of lattice constant of VN, and the decrease of coherency strain between VN and matrix, which is beneficial for the suppression of local diffusion around VN. These changes could be the reasons for the reduction of CRS of HAZ.
In order to clarify the factors that affect the creep rupture strength (CRS) of multi-layered welded joints 9Cr-1Mo-V-Nb-N steel, creep rupture tests were performed utilizing either the double cycle of welding heat simulation or electron beam welding. Metallurgical and mechanistic considerations were given to find guides for improving CRS of the welded joints. The CRS was affected by first cycle temperature (T1) of double-cycled simulated heat affected zone, where T1 were varied from 800 to 1, 400°C, the second cycle temperature (T2) was fixed at 950°C, and then post weld heat treatment (PWHT) was given. When the T1 is lower than 1, 000°C, the CRS is as low as the lowest value of the single cycle test. When T1 is higher than 1, 000°C, the CRS is higher for higher T1. This means that the CRS is improved by multi-layered welding. When T1 is higher than 1, 000°C, the second cycle of 950°C produces dense precipitation of (V, Nb) N which precipitates during PWHT. This results in the improvement of CRS. The CRS of welded joint is affected by the angle between the directions of applied stress and fusion interface. With the angle of 45 degrees, the CRS is most degraded ; the creep repture time is almost one-third of the base metal. For the prevention of the degradation of CRS, the bevel angle should be less than 18 degrees.
In an argon-oxygen gas mixture, pure iron plate was welded by gas tungsten arc welding process. The oxygen absorption behavior by the pure iron weld metal has been investigated metallurgically. The oxygen content of the weld metal increases with an increasing welding current and a decreasing arc length. Traveling speed has only minor effect on the oxygen content of weld metal. With a rising oxygen partial pressure, the oxygen content in weld metal considerably increases, and then gradually increases. In the high oxygen partial pressure region, the oxygen absorption behavior in unlike in comparison with that of the gas metal arc welding process. It is possibly caused by the slow down of oxygen absorption rate in gas tungsten arc welding process.
The effect of tungsten on the HAZ properties in duplex stainless steel was investigated to obtain the high pitting corrosion resistant duplex stainless steel. The steels tested were the modified 25%Cr SUS329J4L duplex stainless steel with the addition of tungsten. The welded joints produced by gas tungsten arc (GTA) welding and simulated HAZ were evaluated in terms of pitting corrosion resistance, impact toughness and microstructures including analysis of precipitates. As results, the tungsten addition up to 2 mass% was effective to improve the pitting corrosion resistance without remarkable deterioration of impact toughness in the HAZ. However, the tungsten addition exceeding 3 mass% decreased the impact toughness in the HAZ as well as pitting corrosion resistance because of accelerating the precipitation of intermetallic compound during the weld thermal cycles. From these findings it was clarified the corrosion resistance of duplex stainless steel is improved in the HAZ by the alloying of proper content of tungsten as well as in the base metal.
It is commonly known that the flux type of covered electrode affects the profile of welds as well as their mechanical properties, and eventually the fatigue strength of welded joint might be controlled. But, there are few investigations performed systematically on fillet welded joint. The purpose of the investigation is to improve fatigue strength of fillet welded joint by appropriately designing the flux of covered electrode. Ten kinds of covered electrodes are produced trially by appropriately adjusting the flux system of covered electrode to 2 levels to improve the profile of fillet toe region and the quantities of added alloy elements contained in each system to 5 levels to vary the hardness of weld metal. By using them, non-load-carrying cruciform fillet welded joints were made, where their base metal was 570 MPa class high tensile strength steel. Fatigue tests (S=σmax-σmin, σmax=σY) were performed by using the fillet welded joints. Main results obtained are summarized as follows: (1) The profile of fillet weld was apparently affected by flux system and base metal and was never affected by added alloy element. (2) Maximum stress concentration factor (Ktmax) at toe was rendered small being Ktmax≅1.59 for covered electrode with MgCO3-MgO-CaF2-Iron powder system flux (M' series). (3) The fatigue strength at 2×106 cycles of fillet welded joint could be improved to about 143 MPa for M' series. It can safely be said that there is an inverse correlation between Ktmax at toe and fatigue strength of fillet welded joint. (4) Recovery of alloy element into weld metal could be revealed to calculating formulae. Recovery of added alloy element was excellent being about 98-85% for Ni, Mo and Cr, and the lowest about 11% for B.
The authors have studied the tensile strength, rotational bending fatigue strength and Charpy impact property of the joints of spheroidal graphite cast iron bonded by diffusion bonding and found that the properties of the joints were comparable to the base metal. In this study, spheroidal graphite cast irons were bonded by diffusion bonding and the effects of nickel foil as an insert metal on the torsional fatigue strength of the joints have been investigated. Main results are as follows ; (1) For the directly bonded specimens after ferritizing, an S-N curve could not be obtained because of large scatters of the fatigue lives at a given stress amplitude due to the presence of fine precipitates of graphite on the interface. However, no failure was occurred for specimens tested for 107 cycles at stress amplitudes below 160 MPa. (2) When the specimens bonded with insert metal of a 10μm thick nickel foil were ferritized, the torsional fatigue limit was 170 MPa, which was lower by 20 MPa than that of the base metal. The difference in fatigue strength at the cycles between 10% and 90% of the failure probability was about 38 MPa ; this is higher by about 16 MPa than that of the base metal. (3) The torsional fatigue limit of the joints having a ferrite and pearlite structure bonded with insert metal of a 10μm thick nickel foil was 210 MPa which was lower by 10 MPa than that of the base metal. However, the difference in fatigue strength at the cycles between 10% and 90% of the failure probability was nearly equal to that of the base metal. (4) The torsional fatigue limit of the joints bonded using a 10μm thick nickel foil increased with increase in the tensile strength of the joints and was about 43% of the tensile strength.
The welding method which provides the welded joint with high performances, especially high bending fatigue strength, at as-welded condition has been studied in consideration of welding residual stress which has an effect on fatigue properties. The results of this study are as follows: (1) The formation of welding residual stress is subjected to three internal stress balances, that are a) the stress balance between the surface and the inside at final welding section followed by the expansion through transformation and the heat contraction, b) the stress balance along the longitudinal direction followed by the heat expansion and contraction of weld metal and HAZ, c) the wholly secondary stress balance followed by the solidification of weld metal and the heat contraction during the welding progress from rail base to rail head. (2) It was found that there is the difference in residual stress between the high C weld and low C-low alloy weld and that the good residual stress distribution of welded joint can be obtained by the combination of both weld metals, and the new welding method has been developed.
This report summarizes the study on numerical analysis of thermal elastic-plastic deformations of steel pipes due to annular local heating process. This process in which while the local area is heated annularly the adjacent sections are cooled can be applied to reduce the diameter of steel pipes. The results of this study are as follows ; (1) While the circumferential plastic strains generated during heating period are compressive, they are tensile during cooling. (2) When the compressive plastic strains remain after cooling, the pipe shrinks. The remaining tensile plastic strains cause the pipe to expand. (3) The variation of the longitudinal temperature distribution controls whether the pipe shrinks or expands. (4) Since the effect of the parameters on deformation of pipe, namely the distribution of temperature, the cross section shape of pipe and the number of themal cycles, can be determined by performing thermal elastic-plastic numerical analysis one can control the deformation of the pipe caused by a forementioned process. (5) The numerical predictions show good agreement with experimental results. Moreover, it is found that the value of pipe shrinkage can be represented by the parameter αTmax/βLc.
A finite element program for three dimensional thermal-elastic-plastic analysis was developed. Because of the geometrical nonlinearity and the temperature dependent material nonlinearities during welding, it is an imprortant problem how to ensure the computing accuracy and to get the stable solution, especially at a high temperature stage. Factors that may influence the accuracy and the convergence of computation were investigated. The results show that the stages with drastic change, such as transition from elastic to plastic, unloading stage, and stage in which material properties vary rapidly with temperature, suffer from the numerical error. When the solid elements are used for the bending problem of a thin plate or a shell, numerical locking phenomenon may also influence the solution. Residual deformations were analyzed by the developed program for two models taken from shrinkage fit process and plug welding process of a compressor. In the program proper methods were introduced to improve the accuracy and the convergence of numerical analysis. One of them is to use weight factors for strain increment in the stages with drastic changes in mechanical status and material properties. In order to prevent the locking phenomenon, the selective reduced integration method was adopted to the cylinder part of the compressor. The calculated deformations were compared with the measured values. The results show that good agreement can be obtained after introducing the proposed methods and that the developed program can provide satisfactory solutions. The influences of the welding conditions upon the eccentricity of assembled components in the compressor were also investigated.