This paper was studied in order to clarify the form and position of transverse crack under actual construction condition with SAW (Submerged Arc Welding) process. In recent years many of the new steel, such as TMCP (Thermo-Mechanical Controlled Process) steel, developments have been intended to improve weldability. TMCP steel have been used achieve high strength with lean compositions, the weld metal is more likely to suffer hydrogen cracking than the HAZ of the parent steel. Weld metal hydrogen cracking is even more likely if alloying is necessary to match the strength and toughness of the parent metal. This is primarily due to the increased susceptibility to hydrogen cracking of more highly alloyed weld metal. But most of the published literature on transverse cracks, so far, different compared to the appearance of transverse crack in actual construction. The reason is a large restraint stress under actual construction compared to a small test piece.
This study is focused on the dependence of microstructure and mechanical properties of maraging steel welded joints on both heat input and pre-weld heat treatment condition. Two different procedures were used for producing fully heat treated welded joints. Procedure I included solution annealing before welding then, aging after welding. Procedure II included full heat treatment (solution annealing and aging) before welding then, aging after welding. It is found that optimizing heat input decreased austenite content and prevented coarsening of weld metal dendritic structure, HAZ grain size and grain boundary precipitates which in turn prevented softening of welded joints. Restoring properties in the HAZ and developing good strength in the weld metal are depended on pre-weld heat treatment condition. Optimum combination of tensile strength, elongation, toughness and structure of welded joints are attained using procedure I. This is due to forming of homogeneous microstructure consisting of fine weld metal dendrites, fine martensite and fine intermetallic compounds in addition to less retained austenite. However, satisfactory welded joints can be obtained using procedure II which should be applied in the case of manufacturing large-size welded assemblies since only the welding zone are treated locally after assembly.
In high frequency electrodes that are composed with a metal substrate and a dielectric coating layer, it is important to clearify the bonding between the metal substrate and the dielectric coating layer and to produce a low dielectric coating layer for electric discharge parts. In this study, the low dielectric coating material is selected the borosilicate glass and the metal substrate is selected the 18Cr-stainless steel by the thermo-electric analysis based on the thermal expansion coefficient of the glass. And it is investigated that the effect of residual stress in the glass in evaluated by thermo-elastic analysis and experiments. Also the interface between the metal substrate and the coating layer is observed from the point of bonding mechanism and is mesured the permittivity in the glass-coated components. As a result, it is showed that the coating layer in thickness of four milimeter could be obtained over the 18Cr-stainless steel by multi-layer coating technique.
For higher reliability of bonding on TCP (Tape Carrier Package), research has been done on the bonding of leads coated with Sn and Sn-Pb on Au bumps formed on LSIs. Major defects of bonding are (1) insufficient bonding, (2) vanishing of Au bumps, and (3) solidification of solder in lumps. Defects (2) and (3) occur when the coating reacts with Au bumps excessively, that is, if the coating is thick or the bonding temperature is too high. As for defect (3), it has been revealed that lumps form when excessive solder flows along the lead and solidifies because its melting point rises as Sn is taken in from the coating. This is more likely with Sn-Pb coating than with Sn coating, probably because the melting point of solder formed at the time of bonding falls due to Pb, allowing reaction to take place more easily. As a result, bonding conditions for practical uses have been formed Sn and Sn-Pb coatings.
For higher reliability of bonding of outer leads to TCP (Tape Carrier Package), research has been done on temperature changes in the wettability of leads, coated with Au, Sn and Sn-Pb, by Sn-Pb eutectic solder. From changes in the wetting force according to the wetting balance method, an apprent activation energy is obtained, with the speed of degradation of wettability defined, dependence on coating thickness measured, and a formula to obtain permissible temperature aging time presented. The speed of degradation is lowest with Au ; it rises much more with Sn. It has been determined that the difference between Sn-Pb and Sn comes from the fact that degradation due to diffusion of Cu (the core meterial of the lead), in the coated layer is more influential than that due to surface oxidation. By forming lap shear joints with test pieces that possess zero wetting force, it is proved that bonding is possible, and that the speed of degradation of strength can be defined like that for wettability.
Alloy tool steel is thought low weldability materials concerning conventional fusion welding process because of high carbon content. Electron beam welding process has the metallurgical advantage and it is likely to be able to apply to alloy tool steel. In this research, the electron beam welding of alloy tool steel as SKS 93 in JIS G 4404 for thickness 16 mm, effects of process parameters and post heat treatment on weld properties have been investigated by observation of penetration shape and defects of welds, measurement of hardness, tensile, impact and EPMA tests. Bead welding were investigated to select suitable welding conditions for prevent defects such as hot cracking and cold cracking and suitable welding conditions were selected. Butt welding were investigated to proper post heat treatment for mechanical properties. Proper post heat treatment were normalizing treatment such as 1113 K and 1133 K for holding time 45 min. Effective application can be expected of the electron beam welding process as a fusion welding process of alloy tool steel.
In this study, aluminum and copper tubes (diameter : 10mm, thickness : 0.5mm) were welded to some kinds of bars by MIW (Magnetic Impulse Welding). The joints welded by MIW were evaluated by water tightness test, tension test and microscopic observation. The most suitable clearance between tubes and bars was 0.5mm for welding under the charged voltage of 14.0±2.5 kV, and it was not dependent on kinds of tubes and bars. Aluminum tubes could be welded with wider clearance than copper tubes, because the plastic deformation of aluminum tubes was easier than that of copper tubes. As bars were harder, tubes were welded better. Degreasing the welded interface had an effect on welding strength. The regular wavy pattern was observed on the welded interface. Microvickers hardness increased as approaching to the welded interface from the base metal of tubes and bars.
Wettability of Cu and Cu-Sn intermetallic compound was investigated in terms of their surface oxidation by spreading and meniscograph tests, and their surface oxides were characterized by SEM, XRD, AES, XPS, TEM and galvanostatic coulometry analysis. In the case of Cu, surface oxidation influenced its wettability a little, although the crystalline Cu2O layer of about 55nm thick was formed on its surface during the heat treatment at 150°C for 2h in air. In the case of Cu-Sn intermetallic compound, surface oxidation appreciably lowered its wettability : spreading factor became smaller, wetting time longer, and wetting force smaller. The surface of the oxidized Cu-Sn intermetallic compound was covered with an amorphous layer of about 5nm thick, while the layer thickness was 55nm for Cu. This thin amorphous layer could not be identified by conventional surface analysis, but its existence was suggested by galvanostatic coulometry analysis. The amorphous layer was identified to be a Cu-Sn complex oxide, by the difference in cathodic potential from Cu2O or SnO. This Cu-Sn complex oxide is more difficult to reduce than Cu2O or SnO because of its lower cathodic potential, which cause the appreciable decrease in wettability of Cu-Sn intermetallic compound.
The accurate measurement of temperature is very important in the material processing. In measuring temperature, it is available to use the radiation thermometer that requires no physical contact with an object, but it is reported that the IR (infrared) radiation thermometer has led to noticeable error in measuring temperature of molten pool where the emissivity is variable. According to the Planck's law of radiation, it is evident that the luminance temperature (measured by radiation thermometry) approaches the true temperature of an object, when the measuring wavelength is shorter than IR. In the present paper, the molten pool temperature measurement by UV thermal radiation has been discussed. In the experiment, stainless steel (SUS304) and mild steel have been melted with GTA (gas tungsten arc) or laser beam, and the temperature distribution of molten pools has been measured with UV sensor (CCD camera, image intensifier and interference filter). As a result, the melting point of metals has been measured with a high accuracy by UV sensor, without correcting the emissivity. The maximum temperature in the molten pool melted with GTA has been 90 K-130 K higher than the melting point, but the maximum temperature in the molten pool melted with laser beam has been much higher than the melting point, when the defocal distance is shorter.
Microstructural analyses of the bonding interface in R-SUS304ULC/Ta/Zr diffusion bonded joints were conducted in order to clarify the embrittlement behavior of the joint. Diffusion bonding of R-SUS304LUC/Ta/Zr was carried out at 1073-1473 K for 0-10 ks in vacuum. SEM and TEM observations revealed that the production layer was formed at the R-SUS304ULC/Ta interface, and that the transition zone existed at the Ta/Zr interface. The intermetallic compounds such as TaFe2, (Fe, Ni)2Ta and TaCr2 were identified in the production layer, however, only Ta was precipitated on α-Zr matrix in the transition zone. The Burgers' orientation relation was almost held between Ta and α-Zr. The hardened area was located at the R-SUS304ULC/Ta and Ta/Zr interfaces, and the severe embrittlement was occurred at the bonding interfaces when the bonding temperature was increased. The growth of the production layer could be expressed by the parabolic growth law, while the growth kinetics of transition zone was complicated during bonding operation.
Recently it has been reported that porous Ti-N sprayed coating became fine structure by laser irradiation. In this paper, we have investigated about the effects of infiltrated metals species for the wear resistance of Ti-N remelted layer. Nonferrous powder metals were sprayed on the substrate of SS400 steel plate in an atmosphere of Ar gas. The coating thickness was about 200μm. Father more, pure titanium was sprayed on the nonferrous spray coating in an atmmsphere of N2 gas. The coating thickness was about 400 μm. The coating specimen consisting of nonferrous layer and Ti-N layer was remelted by laser irradiation in atmosphere of N2 gas. Remelt layers of the coating consisted of fine microstructure and their's hardness values were above HV1000. The wear resistance of Ti-N coating was improved remarkably by remelting.
The low-pressure plasma spray coating process has been established in gas turbine and is used for some parts, such as turbine blades and duct segments, which are exposed to corrosive gases at high temperatures. Overlay coatings based on the MCrA1Y alloy system (M is Ni and/or Co) are commonly employed as oxidation- and corrosion-resistant coatings. Mechanical properties, such as short-time tensile strength and creep-rupture lives, of CoCrA1Y- and CoNiCrAlY-coated systems were investigated at high temperature and compared with the uncoated substrates, such as equiaxis IN738LC, directional solidified CM247LC and single-crystal CMSX-2. As a result, it was clarified that MCrAIY coatings had no significant influence on the tensile strength and creep lives at high temperature. However, the tensile strength at room temperature was reduced for the low-ductility of MCrAlY coatings.
The creep rupture properties of 9Cr-Mo-W welded joints were studied. The creep rupture property of HAZ was also studied by means of simulated HAZ subjected PWHT (Post Weld Heat Treatment). The effect of W on creep rupture strength of welded joint was discussed. The creep rupture tests of GTA welded joint were conducted. The longest stress rupture time is about 20000 hours. In the creep rupture test, the welded joints ruptured in the base metal at higher applied stresses, while they ruptured in the fine grained HAZ adjacent to the base metal with low ductility at lower applied stresses. When the welded joints ruptured in the base metal, the creep rupture strength was as high as that of the base metal. However, when the welded joints ruptured in HAZ, the creep rupture strength of welded joints was lower than that of the base metal. The crack which occurred in HAZ was Type IV cracking which tends to occur in the welded joints of ferritic heat resistant steel. In the creep rupture test, the simulated HAZ heated up to a temperature around Acl and Ac3 temperatures gave lower creep rupture strength than that of the base metal. Especially the simulated HAZ heated up to Ac3 temperature gave the lowest creep rupture strength. The Type IV cracking owes to the fine grained HAZ. The comparison of creep rupture strength of welded joints between 9Cr-Mo-W and 9Cr-Mo-Nb-V (Mod. 9Cr-Mo) indicated that W improved the creep rupture strength of welded joint as well as base metals.
It is important to understand the liquid surface configuration, meniscus configuration in brazing and soldering process. In this study, meniscus configuration formed on circular rod base metal during brazing and soldering has been investigated using computer simulation. Meniscus configuration is determined by combining the Laplace equation and hydrostatic pressure. The meniscus configuration on the plane surface could be determined by simple equation, however, on the curved surface it could be obtained only by the numerical analysis. In the present study the meniscus configuration on circular rod was simulated by Runge-Kutta method. The effects of radius of rod on meniscus rise height and its configuration were investigated. It was found that the meniscus height became small with decreasing the radius of rod. Meniscus configuration of various brazing metals having different surface tension and density were also simulated. Within the present estimation, aluminum brazing filler metal offered the largest meniscus rise height, whereas, Sn-Pb solder gave the smallest one. Similarly, the meniscus configuration depending on the contact angle and the volume of liquid metal was also derived by the present method, therefore, this method is effective to obtain the accurate meniscus configuration of brazing filler metals and to prevent brazing defects such as overor in-sufficient brazing.
A method to measure the surface tension of liquid solder alloys has been developed by the use of wetting balance. In principle, non-wetting Al2O3 rod was immersed into the molten solder bath under the fixed speed. The force acts on Al2O3 rod was measured and then the surface tension was calculated by analyzing the measured force. The theoretical model was based on the hypothesis that the meniscus configuration of molten solder gradually varies depending on the depth of rod and its radius, and also the configuration shows stable form when the depth exceeded the critical value. After exceeding the critical depth, the force increased in proportion to the depth of rod, therefore, the surface tension could be measured by analyzing the obtained force-time curve. As a result, the surface tension of 63Sn-37Pb solder (504 K, in air atmosphere) was 0.53 N/m ; the value is reduced by the use of soldering flux. The surface tension of Sn-Ag-Bi system lead-free solders have been also measured. Increasing of Bi content decreased the surface tension. The effect of flux on the reduction of surface tension is similar to that in 63Sn-37Pb solder.