Microbially influenced corrosion (MIC) of stainless steel welds has occurred in natural sea water or fresh water. SUS304AB containing Ag has an antibacterial ability. The antibacterial ability of SUS304AB against Bacillus megaterium and Pseudomonas putida was investigated using the film adhering cell suspension method, and also the effect of weld scale on the MIC resistance was investigated by means of corrosion tests for 140 days. The results were as follows; (1) SUS304AB has an antibacterial ability against Pseudomonas putida, but not to Bacillus megaterium. (2) Bacterial adhesion on SUS304AB welds has been reduced to 1/10 that on SUS304 welds, however corrosion pits were observed by SEM. (3) The occurrence of corrosion pits was prevented by means of the weld scale removal by brushing, polishing and pickling, although the bacterial adhesion on SUS304AB welds could not be prevented.
This paper has dealt with the feasibility of friction-stir welding a zinc-coated steel plate to a pure aluminum plate in a lap joint configuration (the aluminum plate was top and the steel bottom). The friction stir welding was carried out at rotation speeds of 16.7-41.7 s-1 and travel speeds of 3.3-5 mm/s. It was found that the performance of the joint depended strongly on the depth of the pin tip of the FSW tool relative to the steel surface; when the pin depth did not reach the steel surface the joint showed quite weak fracture loads, while the penetration of the pin tip to a depth of 0.1 mm under the steel surface significantly increased the joint strength. The joint strength tended to increase with rotation speed and slightly decrease with the increase in the traveling speed. As compared with the similar joints of an aluminum to a steel without Zn-coating, joints of aluminum to the Zn-coated steel exhibited high strength at all bonding parameters employed in this investigation, which suggested the beneficial effect of the Zn coating on the bond strength.
We tried to bond two dissimilar combinations, 5052/SUS304 and 5052/SPCC, by ultrasonic spot bonding. The bondability of bonds was evaluated by performing ultrasonic testing and tensile shear test. In principle, good bonding was obtained by ultrasonic bonding without developing any intermetallic compounds. A good correlation between results of ultrasonic testing and tensile shear test could be obtained by selecting the appropriate threshold level in the ultrasonic testing. The microstructure in nano-scale order was observed near the bond interface using TEM to make clear the mechanism of the bonding. We could notice that amorphous structure was developed near the bond interface and this contributed the good bonding of the dissimilar materials by ultrasonic bonding.
A parallel multi-frontal solver is developed for finite element analysis of arc-welding process, which entails phase evolution, heat transfer, and deformations of structures. We verify the code, which is implemented using the hyper-elastoplastic formulation based on Simo and Miehe, via comparison to a commercial code, SYSWELD. Attention is focused on the implementation of the parallel solver using MPI library, on the speedup by parallel computation, and on the effectiveness of the solver in welding applications.
Feedability of welding wire is controlled by sliding contacts between contact tube and wire surface. It is very important for the stable arc discharge that feeding speed of wire does not deviate from the constant speed derived from average welding current. Temperature of contact tube, current branch, voltage drop, and contact resistance of the sliding contact were measured during welding of Cu-coated and non-Cu-coated solid wires. The sliding contacts of Cu-coated solid wire have both states of solid and liquid depending on welding current. On the other hand, the sliding contacts of non-Cu-coated solid wire have a state of liquid without depending on welding current. Discontinuity of solidification at the sliding contacts causes feeding resistance of welding wire. Shearing strength of bridge solidified at sliding contact is about 4.5N, and this force is amplified in liner tube to about ten times. The amplified force is feeding resistance of welding wire. Deviation of wire speed is 43% to average wire speed assuming spring constant of welding wire to be 6600N/m.
Stable sliding contact is the most important factor for stable arc discharge of solid wire. If the contact tube wore seriously, arc discharge would become unstable and wire position would be shifted. Ordinary non-Cu-coated solid wire has much wear of contact tube about ten times comparing to Cu-coated solid wire. The mechanism of contact tube wear is not only friction at high temperature but also molten bridge formed between contact tube and wire surface. Some complex of superfine particles decreases the amount of contact tube wear. For example, the mixture of graphite and magnetite reduces the amount of contact tube wear by 80%. These particles form interface layer on inner surface of contact tube, and the layer prevents the transfer of molten Cu to wire surface. The interface layer mainly consists of FeO and complex oxides.
This paper deals with the welding chamber applied to gas-shielded arc welding under the environment of strong wind. Basically, gas-shielded arc welding method itself is established technology but it is assured the welding quality only in calm environment. Generally, it is necessary to keep the wind velocity at 1.5m/s or less. The fluid chamber reported in this paper can protect against the wind velocity at 7m/s by coaxial jet what is called air curtain. This original coaxial jet generates a laminar swirl flow formed by plural "Partitions" arranged inside of the slit nozzle and assures the welding atmosphere in calm.
This paper deals with the Fluid Chamber applicable to gas-shielded arc welding in strong wind environment. In the case of single annular air curtain jet structure, this air curtain jet becomes turbulent in the groove position, this turbulent flow invades into welding atmosphere along the groove, and welding becomes impossible. The main causes of this phenomenon are for a part of jet stream invading into welding atmosphere along with the groove according to the big pressure slope generated in the inner side produced by the thrust of annular air curtain. So, this paper reports the subject solution method based on the above-mentioned phenomenon.
Generally, plasma welding method is difficult for applying to fillet weld, because of its big plasma force and big torch head. In this report, theplasma welding method of 0.6-2.0mm thick plate which becomes to able to weld easily is investigated, aiming to plasma force. Although plasma force shows to ten times of TIG arc force, it decreases to set small pressure and flow rate of plasma gas. So, it enables to weld various joints by using the plasma welding method setting those small plasma force condition and short stand off length. In the case of small size fillet welding using this method especially, it is successful by using Ar+5%H2 shielding gas and high frequency pulsed current control.
Arc sensors have been widely used for real-time weld-seam tracking in various applications of MAG (Metal Active Gas) welding. Among the applications, the high-speed oscillating MAG process has an advantage over conventional MAG process in the accuracy and fast response of seam-tracking control due to its high sensitivity. For a relatively low current MAG welding in which short-circuiting transfers occur, however, fluctuations in the sensing signals caused by the electrical short-circuiting reduce the sensitivity. The present paper describes the characteristics of the arc sensor focusing on the sensitivity to the torch oscillating frequency f in the low-current and high-speed oscillating MAG process. First, a mathematical model of the short-circuiting droplet transfer phenomena is established based on a conventional mathematical model of the spray transfer phenomena in MAG welding. Then, the relationship between f and the number of short-circuiting Ns is discussed using the model. Numerical calculation results reveal that, when f equals to around half Ns0, which is the value of Ns during welding without torch oscillation, short-circuiting transfers regularly occur at both the oscillating edges and the findings agree with the experimental results. Finally, numerical analyses in the frequency-domain show that the arc sensor indicates the maximum of sensitivity in a specified frequency range that short-circuiting transfers are synchronized with the torch oscillating motion. As a result, when f is set at around half Ns0, the sensitivity is maximized and an accurate control can be achieved in the high-speed oscillating MAG process even at low current levels.
High power laser is a promising tool to weld heavy section plates. One of the major problems, in this case, is formation of some weld defects such as porosity and hot cracking. A final goal of a series of our investigations is to develop defect free laser welding process with the depth of more than 20mm. In the present study, characteristics of deep penetration welding have been investigated using a 20kW CO2 laser facility. Deep penetration of more than 20nm can be attained even at a high welding speed 16.7mm/s. However, porosities are always observed in the longitudinal sections, more significantly for upper focusing conditions. The porosity is not observed, on the other hand, with nitrogen shielding, although large plasma periodically formed during welding and leads to significant reduction in the penetration depth. Pulse modulation of the laser power at the same frequency and duty of the periodical plasma formation can effectively decrease the porosity formation even with helium shielding. This suggests the possibility of porosity prevention by laser power modulation. Dissolution of nitrogen in the molten pool has also good effect to prevent the porosity with nitrogen shielding.
New methods of triggering arc discharge using a plume and a plasma channel in a tungsten inert gas (TIG) arc welding system were demonstrated. The plume and the plasma channel were produced by pulsed laser focusing on an aluminum alloy plate (anode) under a tungsten rod (cathode). The plume was ejected from the laser focusing spot. The plasma channel was generated by gas breakdown in laser beam path. To avoid oxidation, argon (Ar) or helium (He) gas is usually used to shield the rod and molten metal of the workpiece from air. Therefore, formation of the plume and the plasma channel was performed in Ar or He gas. The disadvantages of the conventional triggering methods that require high-frequency generation, high-voltage pulse, or may cause sticking of the rod to the plate are removed in the new methods. The minimum laser energy required for the triggering using the plume and the plasma channel was investigated. Results in this study indicated that laser energy required for the triggering using the plume in Ar gas was lower than that in He gas and that laser energy required for the triggering using the plasma channel in Ar gas was lower than that using the plume in Ar gas. It was found that plasma channel formed by pulsed laser focusing in Ar gas is preferable for triggering arc discharge in the TIG arc welding system.
Hollow Cathode Arc (HCA) was developed as a plasma source under the condition of low pressure in the 1960s, and various researches were performed to make clear the mechanism of the HCA. Since the HCA is a plasma source under low pressure environment, it attracts attention as a welding heat source in space. Moreover, the HCA is expected to be useful for the industrial application on the earth, because the melting process by HCA is very active and the penetration is huge in comparison with that by the conventional GTA. In the previous paper, the discharge and melting process by the HCA has been discussed, and it has been shown that a concentrated columnar arc and a huge penetration are obtained in the case of low gas flowrate. In the present paper, the current distribution on the anode surface and the floating potential of the HCA column have been made clear and the plasma structure of the HCA has been discussed to understand the heat input to the anode by the HCA. It is concluded that the huge penetration by the HCA in the case of low gas flowrate is closely related to concentrated current distribution on the anode surface and the strong flow of electrons in the HCA.
Numerical model to calculate the fraction of liquid phase which takes into account the formation of crystallized phase during welding solidification was proposed in order to predict the solidification cracking susceptibility of high Ni steel weld metals. For evaluating the validity of the proposed model, changes in the fraction of residual liquid phase on solidification process for Fe-36%Ni-0.02%C-1%Nb weld metal solidifying at nearly γ phase and Fe-36%Ni-0.2%C-1%Nb weld metal solidifying with niobium carbide during γ solidification were quantitatively investigated as follows. After each quenched solidification microstructure of these weld metals was made by liquid tin, the change in the fraction of residual liquid phase for Fe-36%Ni-0.02%C-1%Nb weld metal was quantitatively evaluated by analyzing the region corresponding to residual liquid phase in SEM (Scanning Electron Microscope) image of the quenched weld metal. Also, Fe-36%Ni-0.2%C-1%Nb weld metal was quantitatively evaluated by separating NbC from residual liquid phase by using the mapping data of Nb and C by EPMA (Electron Probe Micro Analyzer). These experimental data coincided with the fractions of liquid phase obtained by using the model for Fe-36%Ni-0.02%C-1%Nb and Fe-36%Ni-0.2%C-1%Nb weld metals and the morphology of niobium carbide predicted by the model also corresponded to TEM (Transmission Electron Microscope) observations. Furthermore, the effects of niobium and carbon contents on the solidification cracking susceptibility of Fe-36%Ni weld metal was able to be explained by using the model.
In order to repair and improve the performance of machinery parts of a power plant, pulsed Nd: YAG laser, CO2 laser, diode laser and TIG cladding were carried out for deposition of Stellite 6 alloy on the surface of 12%Cr martensitic stainless steel plate (t=12mm). These clad layers were characterized by investigating cross sectional geometry, microstructural features and DAS (Dendrite Arm Spacing) values, dilution, macro- and micro-distribution of alloying elements, primary and eutectic phases, hardness distribution and wear resistance by microscope, SEM, EDS, EPMA, X-ray diffractometer, Vickers hardness tester and Oogoshi wear resistance tester. The small dilution ratios, fine microstructures, narrow widths of heat-affected zones, high Vickers hardness, excellent wear-resistance, high contents of Co and low contents of Fe in the clad layers were obtained by laser cladding in comparison with TIG process.
Diffusion bonding and explosive welding of oxide dispersion strengthened silver (ODS-Ag), which is one of electric contact materials, to copper (Cu) have been conducted to compare their interfacial microstructures and bonding strength. The diffusion bonding was carried out at 973 K for 3.6 ks to achieve solid state bonding. Defects like void were observed at the interface in the diffusion bonded ODS-Ag/Cu joint. It is considered that insufficient contact at the interface is responsible for the formation of the defect. The shear strength of this joint was less than 40 MPa and far inferior to that of Ag/Cu joint produced under the same condition. On the other hand, the explosively welded joint had no defects in the collision interface. Its bonding strength exceeded that of the diffusion bonded Ag/Cu joint, and was about four times as high as that of the ODS-Ag/Cu joint fabricated by diffusion bonding. From the results of TEM observations, microstructural aspects of the ODS-Ag in the vicinity of the collision interface appear to be similar to those observed before bonding. This suggests that the characteristics of the ODS-Ag as a electric contact material are retained even after the bonding treatment. Therefore, the solid state bonding with momentary high pressure such as explosive welding is suited to the bonding method for the ODS-Ag materials.
Recently the reduction of the product cost is rapidly advanced, and the demand that must join the cast iron to mild steel is heightening. At present, for the joining of cast iron and mild steel, the mechanical joining using the bolting is usually carried out, and it becomes a cause of the cost increase. If the welding can be applied to the joining of cast iron and mild steel, the contribution to the manufacturing industry will be large. But when welding engineers consider the welding of these materials, they do not have the appropriate answer for the welding process and the welding consumables. The welding of cast iron and mild steel is possible. In actuality, the researches on this welding have been carried out. The researches are divided into 2 types. The first is the examination of the weld zone made by changing the filler metal, the flux and the welding wire in same welding process. The second is the examination of the mechanical property and the structure in weld pieces made by one welding process. Therefore the papers in which various welding processes are applied for the material of same condition and then the welding results are examined have not been published yet. In this study, 11 kinds of test pieces are produced using 4 kinds of generally used welding processes. And in the viewpoint of the practicability, the welding of cast iron and mild steel is examined from hardness, tensile strength, elongation, impact strength, weldability (workability), efficiency and cost. As the result, that the metal-arc active gas welding using the solid wire for mild steel is suitable for the welding of these materials clarifies.
Fracture behavior of high strength linepipes with weld defects is of great interest for the integrity of pipeline system. Especially, in the seismic or permafrost area, where large grand displacement can be expected, linepipe materials need to have sufficient resistance against brittle and ductile fracture under large deformation. Since large weld flaw can be eliminated by recent advance in material, welding and inspection technology, ductile fracture must be a next concern for high strength linepipe. Therefore, ductile fracture behavior of girth weld joints of Grade X80 and X100 linepipes were investigated in this study. Wide plate tensile tests were conducted using girth weld joints with the surface notch in the weld metal. Close observations were conducted in order to determine crack initiation from the notch root of the wide plate specimens. Local stress-strain conditions were evaluated by 3-D FE analysis, and criterion for ductile cracking were compared with that was obtained by small-scale specimen. Results showed that ductile cracking behavior is strongly affected by hardening properties of the base materials. Resistance to cracking in girth weld metal can be improved by applying the materials with lower Y/T ratio even with the similar weld metal property, and over-matching of the weld metal should be important condition. Concepts for defect assessment in terms of preventing ductile cracking are discussed with regard to the effect of base metal properties and strength matching of girth weld joint.
780MPa class high strength steel has a problem concerning about work hardenability because of many dislocations in the martensite matrix due to the mechanism of transformation itself. In previous report1), it is pointed out that poor work hardenability may decrease ductile crack initiation property. For this problem, three metallurgical methods were investigated aiming to improve uniform elongation. (increasing Fe3C, increasing Ni, refinement of γ grain). In this paper, two newly developed steels are manufactured in laboratory scale taking those methods into consideration. Property of ductile crack initiation of developed steels is evaluated in two ways. One is the method by small round bar tensile specimen. The other is the method by specimen supposed to be real penstock structure. Finally, according to these two tests, superior properties of work hardenability and ductile crack initiation are clearly observed in developed steels. Through this study, it is known that increasing intragranular pile-up site on the assumption of martensite structure can control property of ductile crack initiation.
The scatter of fracture toughness in the ductile-brittle transition temperature region was experimentally examined on 500 MPa class low carbon steel. The repeated toughness tests with the three points bend specimens were carried out at -60°C, -20°C and -10°C. The Weibull statistics of the fracture toughness K(Jc) at -60°C showed the single modal distribution with the shape parameter of around 4, which agrees with the analytical prediction from the conjunction between the Weibull stress analogy and the fracture mechanics. The Weibull distributions of the K(Jc)s at -20°C and -10°C, however, showed the typical bilinear pattern with the elbow point. The Weibull slopes below the elbow points were closed to the value of 4, but the slopes showed the transition to be smaller slope at the elbow points. The K(Jc)s above the elbow points induced the larger scatter of the data set at -20°C and -10°C. The fracture surface observations revealed that the K(Jc)s of the elbow points on the Weibull distributions are coincided with the stable extension of around 0.2mm or 0.3mm in length. This transition condition in the Weibull slope were also discussed, compared with the JIc value and the required conditions for δc or Jc prescribed in BSI and ASTM. The bilinear Weibull distributions experimentally obtained were also simulated by the analytical model, in which the Weibull stress criterion was applied to the stably extending crack tip. In spite of the simplified model with the radical approximation, the analytical model could describe the trend of the bilinear Weibull distribution.
In order to improve high temperature property of the dissimilar joint between 0.5%Ti-0.07%Zr-Mo and graphite, Nb-Ti and Nb insert metals as well as a conventional Zr diffuse material were used for bonding. Cross-sectional observation and EPMA analysis were carried out to evaluate the joining process. Mo did not diffuse into bonding layer at low joining temperature. However, diffusion of Mo into bonding layer was significantly observed at high joining temperature. For Nb-Ti insert metal, Ti-rich dendritic Ti-Nb-C solid solution layer was formed near the graphite side in bonding layer. This layer indicated high hardness. Diffusion of Mo from 0.5%Ti-0.07%Zr-Mo suppressed growth of the Ti-Nb-C solid solution layer at joining temperatures above 2073K. The joint with Nb-Ti insert metal indicated higher bending strength than that of the joint with Zr solder material above 1673K.
At GLC project, pair of liner accelerators will be built, facing each other as 33km total length and needs 18000pcs of 60cm X band accelerator structure. Now the manufacturing process of it is diffusion bonding with 72 hours, but we have to reduce process time. And so we tried direct bonding for 60 pcs OFC disk blanks with pulse current. Concerning this experiment, we developed new equipment which was an elastic electrode (CCE) for direct bonding. Then we got satisfied results on a basis experiment for accelerator structure manufacturing.
The metallographic factor controlling the strength of friction-welded interface of Al-Mg alloy 5052 to mild steel S10C has been investigated in nano-scale mainly by TEM observations. The bond strength, estimated from the tensile strength of a specimen with a circumferential notch at the interface, increased rapidly with an increase in friction time and then reduced when the friction pressure was 20MPa. A maximum strength of 327 MPa was obtained at a friction time of 4 s (rotation speed = 20 s-1 and forge pressure = 230 MPa). At a friction time of 1 s, the interface consisted of areas where an IMC(Intermetallic compound) layer about 30 nm wide was formed and areas where no IMC layer could be detected. In addition, an Al oxide film of a width less than 10 nm was observed at the interface of the mild steel substrate to the IMC layer and Al alloy substrate. With an increase in friction time, the volume of the IMC was increased and the Al oxide film remained in narrower areas to be almost disappeared at the maximum bond strength. At friction times shorter than that to obtain the maximum bond strength, fracture occurred mainly along the Al oxide film, suggesting that the bond strength was controlled by the Al oxide film. At friction times longer than that to obtain the maximum bond strength, joint were fractured in the IMC layer, which occupied almost whole areas of the interface. The bond strength of these joints decreased almost linearly with the increased in the width of the IMC layer irrespective of the friction time and pressure. Thus the factor controlling the bond strength can be considered to alter from the Al oxide film to the IMC layer with the increase in friction time. The IMC layer consisted mainly of Fe2Al5 and Fe4Al13. Small amount of FeAl2 was also detected. These compounds were granular and distributed randomly in the IMC layer. The width of the IMC layer was increased almost in proportion to the friction time at a rate which rose with friction pressure. These results suggest that the growth of the IMC layer is controlled by mechanical mixing of Al and Fe at the interface as well as the diffusion.