Al-clad materials were fabricated from commercial aluminum alloys of A1050, A1100 and A3003 as an overlay plate, mild steel SS400 and stainless steel SUS304 as a base plate using three methods of explosive bonding as well as roll bonding in air and roll bonding in vacuum. The isothermal heat treatments at 580 to 650°C for 0 to 60 s were given to the Al-clad materials to study the formation of Al-Fe intermetallic phases. Main results obtained are as follows ; (1) FeAl3 and Fe2Al5 were formed in the bond interface of the Al-clad steels, and only (Fe, Cr, Ni) Al3 was formed in the bond interface of the Al-clad stainless steel. (2) The highest growth rate of these phases was in the bond interface of the explosively bonded Al-clad steel, the second highest rate was in the Al-clad steel roll bonded in vacuum and the lowest rate was observed in the Al-clad steel roll bonded in air. (3) Effect of the purity of the aluminum alloys on the formation of the intermetallic phases was not readily noticeable. However, the growth rate in the bond interface of Al-clad steel fabricated from high purity aluminum (99.99 mass%) was the highest of all Al-clad steels roll bonded. (4) The thickness of the intermetallic phases in the Al-clad steels was larger than that in the Al-clad stainless steel under the same isothermal heat conditions.
Several kinds of cermaic particles were plasma sprayed and collected on the metallic flat substrate surface held at various temperatures. Effects of both solidification and wetting at particle/substrate interface on the flattening behavior of the particles were investigated. The linear relation between transition temperature and thermal conductivity of the particle was clearly observed, and the worse the wettability at particle/substrate interface was, the steeper the gradient of the line was. This result indicates that even in the ceramic particles, the rapid solidification at the bottom part of the splat occurs when a temperature of the substrate is close to the transition temperature. The central disk part in the splash splat diminished gradually with decreasing the substrate temperature. Wholly scattered splat could be often observed when the wetting of the particle to the substrate was bad, like in the case of alumina splat on the gold coated metal substrate. Therefore, the occurrence of the splash splat does not always need the rapid initial solidification at collision of the particle to the substrate. Consequently, the wetting seems to be the most dominating factor in the flattening of the thermal sprayed ceramic particle on the substrate. The rapid solidification is thought to affect on the flattening of the particle when the wetting reaches to some moderate condition.
Generally, GMA welding method is used to high efficient welding process of stainless steel. In this paper, aiming to establish the suitable welding procedure, MIG and MAG welding method of 3-9 mm thick SUS304 plate are investigated. In MIG welding method using solid wire, the short arc welding conditions with pulsating control arc effective in various welding operations. On the other hand, in MAG welding method using flux cored wire, the suitable arc voltage conditions are about 2V upper than short circuiting voltage. In each welding methods, the suitable welding conditions of various kind of joints are easily found by using the graphs those show the relationship between welding condition and the volume of wire deposited metal for unit welding length(Vw).
In horizontal position, welding bead has an inclination to become hanging bead by gravity, and this problem makes horizontal welding difficult for high-deposition rate welding. A new basic concept so called Electromagnetically Controlled Molten Pool (ECMP) welding process that used electromagnetic force was proposed to solve this problem, and it was proved the possibility by new TIG welding process (1 wire type) with ECMP in horizontal position. In this paper, TIG welding using 2 filler wires with ECMP is proposed for higher deposition rate welding in horizontal position. 2 filler wire feeders are connected in series to a. wire heating power source, and one wire is inserted at front position, and another is inserted at rear position of the arc. So, joule heating ability and heat exchanging ability to the arc is increased comparison to 1 wire process. Farther more, area of unidirectional current in molten pool is increased by this wire arrangement. So, more wide upward electromagnetic force compared to 1 wire type is generated, and controlling ability of bead shape is increased under magnetic field. In the test, wire melting characteristics were investigated, and it was found that stable welding was possible under high deposition rate such as 100-150g/min. Bead shape was improved remarkably, and contact angle of bottom side in weld bead was decreased under the half of magnetic flux density that was required in lwire process. V groove joint weld was done for stainless clad steel, and good penetration, smooth bead shape, sound weld joint property was obtained under high deposition rate welding condition such as 100 g/min. After these basic tests, new 2 wires type TIG welding process with ECMP was applied to huge steel structure, and practicability of this process was proved by successful result.
In order to advance automatic arc welding and progress quality of welding, the spot laser sensing system has been developed which can be used by general articulated welding robots. The sensor head is attached to the side of welding torch when sensing and detached before welding because of ensuring approach to narrow areas and avoiding influence of arc. It is the main characteristic of this sensor that the robot user can easily introduce exclusive functions for each work piece. In this study, sensing practical applications have been developed for the purpose of improving functions of wire touch sensor and realizing new functions. As a result, it is ascertained to be able to correct welding points and decide welding conditions by measuring groove shapes. Furthermore, evaluating quality of welding becomes possible by measuring inspection of weld bead shape in the same system.
The characterization of reheat cracks in FCAW weld metal of a fluid catalysis cracking (FCC) unit has been performed to clarify the effect of bismuth on the reheat cracking sensitivity, and y-groove self-restraint cracking tests have been carried out with FCAW weld metal containing various amounts of bismuth. As for the weld metal of practical construction, the fractured surfaces of reheat cracks showed a dendritic appearance and cracks mainly propagated along the columnar grain boundary. No evidence of liquation was observed on the fractured surface. During the y-groove self-restraint cracking test, reheat cracking occurred only in the bismuth-containing weld metal at temperaturs above 823K during heating or holding. The reheat cracking sensitivity was increased with increasing bismuth content in the weld metal. The results of the cross sectional observation showed that the crack initiated at the root of the test bead and mainly propagated along the columnar grain boundary. The fractured surface showed a dendritic appearance. Based on these observations, the cracks that occurred in the y-groove self-restraint cracking test are similar to those that occurred in the weld metal of the FCC unit. Therefore, the y-groove self-restraint cracking test reproduces the reheat cracking in weld metal and bismuth is considered to be the main factor that causes the reheat cracking in the FCAW weld metal during operation.
To evaluate the high temperature ductility, which is considered to affect the reheat cracking sensitivity, creep rupture tests with Type 308 stainless steel weld metals made from various commercial welding materials at 823 K-1023 K have been performed. To clarify the effect of bismuth on creep embrittlement, creep rupture test with FCAW weld metal including Type 308, Type 316 and Type 347 containing various bismuth contents have been carried out at 823 K and 973 K. The experimental results indicate that with an increasing Larson-Miller parameter value, the rupture strength of the Type 308 weld metal decreased linearly with decreasing rupture ductility. Among the welding processes using commercial welding materials, the FCAW weld metal showed the poorest rupture ductility. However the bismuth-free FCAW weld metal showed a better ductility compared to the bismuth containing FCAW weld metal. It is concluded that the main factor which causes creep embrittlement in the FCAW weld metal is bismuth which is usually added to the flux for improvement of slag detachability. Also, the Type 316 and Type 347 weld metals were embrittled by bismuth as in the case of the Type 308 weld metal. The characterization of cracks in the creep rupture test specimen indicated that regardless of the bismuth content in the weld metal, the fracture mechanism can be categorized into two types, the transgranular type and the intergranular type. At the higher test temperature and/or the prolonged rupture time, the intergranular type fracture becomes dominant and the rupture ductility decreases. Bismuth is considered to severely affect the grain boundary embrittlement and enhances the degradation of rupture ductility.
According to previous reports, the main factor causing reheat cracking in stainless steel FCAW weld metal is bismuth added in the flux to improve slag detachability. The cracks, whose surfaces have a dendritic appearance, propagate along the columnar grain boundary. In this report, the constant speed tensile test at elevated temperature in an inert gas atmosphere was performed and the ductility of the FCAW weld metal was evaluated to clarify the temperature range of weld metal embrittlement, and characterization of the fractured surfaces was performed to categorize the fracture type. Also, the effect of initial ferrite content and precipitates such as the σ phase on the ductility was evaluated. As for the bismuth-free weld metal, a significant ductility drop was not observed at any test temperature and the fractured surface showed a dimple pattern which suggests a ductile and transgranular fracture. On the other hand, in the case of the bismuth-containing weld metal, ductility is remarkably depressed at temperatures above 873 K and the fractured surfaces showed a dendritic appearance. Moreover, at temperatures above 1173 K, the fractured surface showed sighs of Equation at higher magnification. The ferrite content in as-welded condition and aging time at 973 K had no effect on the ductility at elevated temperature. Therefore bismuth is the main factor that causes the grain boundary embrittlement at elevated temperature. However, in the case of the high ferrite content under as-welded conditions, the aged weld metal showed slightly depressed ductility compared with the low ferrite content material, therefore, the precipitates in ferrite are considered to be a secondary factor for reheat cracking.
According to previous reports, columnar grain boundary embrittlement caused by bismuth is responsible for the reheat cracking of Type 308 FCAW weld metal. It is necessary to quantitatively evaluate the reheat cracking sensitivity for comprehension of the reheat cracking mechanism. It is considered that grain boundary cracking at elevated temperatures occurred when the strain due to creep deformation caused by residual stress in the relaxation process reached a critical value in the neighborhood of the grain boundary. Therefore it can be said that this critical strain represents the reheat cracking sensitivity of the weld metal. In this report, a constant load tensile test using a notched specimen is performed and the reheat cracking sensitivity of weld metal is quantitatively evaluated by crack opening displacement (Φc) which corresponds to the critical strain of a grain boundary fracture. The results show that Φc is reduced with increasing bismuth content and increasing test temperature. At temperatures above 1100 K, Φc is remarkably decreased in the bismuth-containing weld metal whose fractured surface shows signs of requation. Φc shows a good relation with the cracking ratio of the y-groove self restraint cracking test. Therefore, Φc quantitatively represents the reheat cracking sensitivity of the weld metal.
In order to make clear the metallurgical characteristics of the heavy steel plate laser weld metal, the effects of cooling process and chemical compositions on hardenability and microstructure of the weld metal. Cooling rate and cooling time in the laser welding process were considerably correlated with the incident laser energy per unit welding length (heat input). Cooling rate and cooling time from 1073 to 773 K of the weld metal of 25 mm thick steel plate, which was welded with laser power of 45 kW and welding speed of 25 mm/s, was estimated at 35 K/s and 8 s respectively. The thermal efficiency in laser welding was almost the same as that in TIG welding, and the efficiency was estimated to be 50 to 60%. The hardness of laser weld metal was proportional to the carbon equivalent, Ceq IIW. Especially the laser weld metal with high carbon equivalent remarkably hardened compared to the submerged arc weld metal. The acicular ferrite structure, which was generally reported to result in high toughness, was also obtained in the laser weld metal containing Ti, O and B by controlling the chemical composition of weld metal in an optimum range. The acicular ferrite in the laser weld metal was finer than that in the submerged arc weld metal. The optimum range of carbon equivalent of the weld metal for acicular ferrite formation became narrow and sifted to lower carbon equivalent area as the cooling rate increased. For welding 25 mm thick steel plate with laser power 45 kW and welding speed 25 mm/s (cooling time from 1073 to 773 K : 8 s), the optimum Ceq IIW was ranged between 0.15 and 0.35 mass%.
Two dimensional microstructural model of the liquid evolution between the matrix and NbC particles on grain boundaries was presented to make the mechanism of grain boundary liquation clear during laser welding of Inconel 718 alloy. The constitutional liquation mechanism was adopted as the basic liquation mechanism of second particles. The numerical analysis of local melting of NbC under welding thermal cycle was divided into three stages such as solution stage, liquation stage and solidification stage. The first of solution stage corresponds to that NbC particles dissolved into matrix during heating process. The second of liquation stage corresponds to that liquation takes place between the matrix and NbC particles and liquid infiltrates along the grain boundary also during heating process. Finally the third of solidification stage corresponds to that liquid phase on grain boundary solidifies during cooling process. During this work, a local equilibrium between the solid and liquid phase was assumed and the compositions at interface were calculated by Thermo-Calc using Ni-DATA as a database. The numerical results suggest that a liquid begin to appear between the particle of NbC and matrix at a temperature of 1439 K and as the temperature increases, the volume of liquid increases. Meanwhile, the liquid infiltrates along grain boundary during heating.
In this study, grain boundary liquation phenomenon using two-dimensional model was calculated in order to estimate infiltration length of liquid phase around precipitate NbC on grain boundary as a function of the temperature. The high temperature ductility test was carried out as a verification of the numerical calculation, and the numerical calculation result was compared with the experimental result. Grain boundary liquation start temperature calculated by the numerical analysis was well correspondent to the temperature measured by the experiment. In addition, the effect of heating and cooling speed, grain size and particle size of NbC on the liquid phase infiltration length to grain boundary in the laser welding was examined by the two-dimensional grain boundary liquation analysis. In Inconel 718, grain boundary liquation started in the heating process at 1434 K. The length of the liquid phase which infiltrates along grain boundary on the heating rate within 5000 K/s was not affected by heating rate. In addition, it was suggested that the liquation crack sensitivity be improved by decreasing grain size and doing the particle size of NbC under 1.0μm.
This study was carried out to select suitable welding methods and welding consumables used for constructing a galvanizing bath. In this report, these were selected in terms of the elevated temperature strength, the susceptibility of liquid metal embrittlement and corrosion resistance in liquid zinc. The base metal used was a carbon steel specialized for a galvanizing bath. The shielded metal arc (SMA) and gas shield arc weldings (GMA) were used with a covered electrode (E1) and solid and flux cored wires (F1, F2 and F3). The elevated temperature strength of all deposited metals were measured at the temperature range from room temperature to 600°C. Moreover, the notched bar tensile (NBT) test, where the bottom of notch was coated by liquid zinc, was performed at the temperature of 480°C to know the susceptibility of liquid metal embrittlement. Corrosion resistance was measured at the temperature of 450°C in molten zinc of practical bath. Strength at the elevated temperature of deposited metals by GMA welding was higher than that by SMA welding. The susceptibilities of liquid metal embrittlement of deposited metals became high in the order of E1, F3, F1 and F2. The susceptibilities of F1 and F3 were almost corresponded with that of the base metal. The susceptibility of liquid metal embrittlement at liquid zinc increased with an increase in the term of C+Si+Mn. Moreover, corrosion resistances of F1 and F2 in liquid zinc were higher than those of the base metal, E1 and F3. When the value of C+Si+Mn exceeds 1.7%, corrosion resistance of weld metal decreases. The solid wire, F3 was. selected as a candidate of welding consumable used for constructing a galvanizing bath from the present results.
The structure and constituents in two types of nickel-base self fluxing alloy coatings thermal sprayed and subsequently fused were precisely investigated by use of X-ray diffraction analysis, electron probe microanalysis, scanning electron microscopy and transmission electron microscopy. JIS-MSFNi1 alloy coating was composed of primary nickel solid solution and Ni3B phase between primary nickel grains with a small amount of Ni-Ni3B eutectic. In case of JIS-MSFNi4 alloy coating, lumpy crystals and two kinds of rod-like crystals appeared in addition to Ni-Ni3B eutectic. It was found that the lumpy crystal is M6C carbide containing chromium, molybdenum and nickel. The rod-like crystals are M3B2 boride of tetragonal structure and M7C3 carbide of hexagonal structure. Metal constitution of M3B2 are chromium and molybdenum and M7C3 contains mainly chromium. The nickel phase in the Ni-Ni3B eutectic of MSFNi4 alloy coating has the superlattice structure.
The effect of bonding misfit on creep rupture properties of TLP-bonded joints of Ni-base single crystal superalloy CMSX-2 were investigated bonded using MBF-80 insert metal. The bonding misfit was defined by ‹100› twist angle (rotating angle) at bonded interface. The post-bond heat treatment consisted of the solution and sequential two-step aging treatments was carried out in the Ar (oxygen partial pressure : 6.7 mPa) or vacuum (oxygen partial pressure : 4 mPa/0.27 mPa) atmosphere prior to creep rupture testing. Creep rupture properties of joints were comparable to those of base metal within the rotating angle being up to 3° while drastically fell down with increasing the rotating angle more than 5°. The boundary energy and oxygen content at bonded interface increased with increasing the rotating angle. Creep rupture properties of joints could be improved with lowering the oxygen partial pressure during post-bond heat treatment attributed to the restraint of grain boundary oxidization of bonded interface. It was deduced that the bonding misfit which promoted the grain boundary oxidization during post-bond heat treatment caused by the increment of boundary energy at bonded interface was deteriorated the creep rupture properties of joints.
The fatigue strength of developed box welds was improved about two times of the conventional box welds. The improved welds used the low transformation temperature welding material which contains 10% Cr and 10% Ni. The expansion of the developed welding material was 0.55% due to the transformation from austenite to martensite. This expansion induced the compressive residual stress around welds. On low stress range condition, the stress ratio effect by this compressive residual stress avoids the fatigue crack initiation at the weld toe. On high stress range condition, the fatigue crack initiated from weld toe and the fretting was observed on the fractured surface. While in the conventional welds, no trace of fretting was observed.
Electrochemical migration is the phenomenon that the electric circuits are shorted by anode dissolution or cathode extraction on a conductor metal surface, when an electric field is done under humidity environment. The growth of an electrochemical migration is largely influenced by a kind of the conductor materials, the insulation resistance between the conductors, or the strength of electric field, because this electrochemical migration is based on the electricity chemical reaction on the surface of conductor material. Noticing to that an electrochemical migration is the electricity chemical reaction associated with transfer of electric charge on a conductor metal surface, in this research it examines about an electrochemical migration evaluation method from an electric charge volume based on potential distribution between a conductor. A current concentration degree in an edge department of an electrode can be made 2 times of electrode parallel departments, by using a electrode with trapezoidal shape. And then, by this current concentration, an occurent place of an electrochemical migration is fixed and the state of voltage potential is difficult to be influenced by other electrode parts. Now, considerating the critical current value for electrochemical reaction instead of the critical voltage potential, electric charge for occurrence of migration can be calculated by leak current above an critical current value. It is conceivable that a case as a standard evaluation scale is possible, to become the criticism value that an electric charge volume reflected insulation resistance between conductors or surface condition of a conductor.