A vacuum roll bonding apparatus has been developed to produce clad metals. Clad metals such as Al/SS41, A5083/SS41, Cu/SS41, Ti/SS41, SUS304/SS41, Al/Cu, Al/Ti, Cu/Ni, Cu/Ti and Nb/Ti were produced at temperature in the range 0.7-0.85 of the homologous melting temperature using the vacuum roll bonding. And bond mechanism on this method, bond microstructure and bond strength of the clad metals have been investigated. The results obtained are as follows: (1) Bondings of dissimilar metals such as aluminum clad steel, which is difficult to bond by diffusion bonding, were performed under the low reduction in thickness. (2) Though the bondings were performed at elevated temperature, interdiffusion of the elements at the bond interface which occurred during the bonding and cooling process was so little that it was not detected by EPMA analysis. (3) Bond shear strength of A5083/SS41, SUS304/SS41 and Ti/SS41 was higher than that specified by JIS. As the bond shear strength of other clad metals was very high, shear fracture at the bond interfaces did not develop on the shear test.
Impact properties at cryogenic temperature of candicate materials for fusion reactor and their electron beam welded joints are investigated by using instrumented Charpy impact testing apparatus. Material used are aluminum alloys (A7N01, A5083, A6061), JFMS (Japanese Ferritic Martensitic Steel) and two kinds of high manganese steels. Although JFMS is a steel for high temperature use, the impact test is conducted at low tenperature same as the cases of the other materials. Testing results are obtained as follows. 1. Base metals and welded joints of aluminum alloys exhibit high absorbed energy at low temperature. Ductility of each base metal and welded joint gradually decreases with decreasing of testing temperature. 2. Base metal and welded joint of JFMS exhibit an absorved energy transition temperature at near a room temperature. 3. Base metal and welded joint of high manganese)steel A-T (18Mn) exhibit abrupt decreasing of absorbed energy at 77K, but base metal and welded joint of high manganese steel B-T (22Mn-0.2N) exhibit gradual increasing of maximum strength and decreasing of ductility with decreasing of testing temperature.
In this paper, the fatigue limits of simulated butt-welded joints were obtained under reversed bending and the results were discussed based on the critical condition for existence of a non-propagating crack. It is well known that there is a close connection between the fatigue strength and the flank angle of a welded joint, as point out by Newman and Gurney. However, the relation shows a considerable amount of scatter. According to the present results, the cause of the scatter can be explained through the critical condition above mentioned.
In this paper, the influence of plate thickness on the fatigue strength of non-load-carrying fillet weld joints is examined both experimentally and analytically, from the view point of weld residual stresses. In order to control the longitudinal residual stresses (in the direction of the weld line), rib-cruciform joint specimens with various plate width were prepared. On the one hand, specimens of which heat input for each pass was varied were also prepared to control the transverse residual stresses (in the perpendicular direction to the weld line). Using these specimens, both residual stress measurement and fatigue tests were carried out. It was found that the plate width of specimen had great effects on the longitudinal residual stresses and little effect on the transverse residual stresses respectively. And it was also found that the transverse residual stresses increased as the heat input decreased. As far as the heat input was constant, the plate width had no effect on the fatigue strength. On the other hand, the heat input significantly influenced the fatigue strength of joints with a same thickness of main plate. That was, the fatigue strength in the case of high heat input was much higher than in the case of low heat input. From above results, it is concluded that the fatigue strength of non-load-carrying fillet weld joints depends on the transverse residual stresses and that the tensile residual stresses increase as the plate thickness increases and/or the heat input decreases, causing the reduction of the fatigue strength.
Repair works by welding on the structures in service condition are often done under the pulsating loads. In this study, the deciding method of the initiation of quasi-solidifiaction crack was investigated by using the results of hot weld crack test under the pulsating loads. Moreover, hot crack was considered from a mechanical point of view. The main results are as follows. (1) The equation for the initiation condition of quasi-solidification crack under the pulsating loads was shown. Moreover, based on it, the equation to decide the initiation of quasi-solidification crack was also shown, in which relative root gap opening displacement, Δδ, that can be easily measured before welding was used as a practical mechanical measure. (2) For the case that the uniform pulsating loads are applied, the practical deciding equation for the initiation of quasi-solidification crack was shown in non-dimensional form. Moreover, applying it to the result of hot crakc test, the validity was concretely shown. (3) Without distinction between solidification and quasi-solidification crack under the pulsating loads, the critical strain curve for hot crack of weld metal used in this study was shown. (4) The main mechanical factor was the product of repeat number of times and Δδ by the external loads concerning the solidification crack and was the opening rate of root gap and the magnitude of Δδ in a cycle concerning the quasi-solidification crack. (5) The concrete procedure to apply the evaluating equation for hot crack, that is solidification and quasi-solidification crack, was shown. Besides, so far as the evaluating equation proposed in this paper is used, critical strain of each crack is not necessary to be obtained.
Coupling effects between the temperature field and the structural changes are considered in the analysis of the laser transformation hardening process. The volume fractions of the structural components, the latent heat during the phase transformation and structure dependence of the thermophysical properties are introduced during the iterational calculations of the temperature distribution and the structural changes. The carbon content, mean value of the grain size of the prior austentite, and the size and the interlamellar spacing of the pearlite colony are input for the initial parameters. Numerical computations are carried out by the finite element method, and the hardness distribution in HAZ can be also obtained
This study evaluated homogenizing process of alloying elements such as aluminum, titanium and chromium during Transient Liquid Insert Metal Diffusion Bonding (TLIM-bonding) of Ni-base superalloys such as MM007, Mar-M247, Inconel 713C and IN939 with a Ni-15%Cr-4%B amorphous insert metal. The detailed analysis at the bonded interlayer of TLIM-bonded joint was performed quantitatively using electron probe microscopy (EPMA) technique. From the experimental results, the concentrations at the center of the bonded interlayer (Ct) of aluminum and titanium increased and that of chromium decreased dependent on the holding time during homogenizing process due to elements diffusion from the base metal to the bonded interlayer. Further, increasing temperature decreased the holding time for completion of homogenizing process. Homogenizing process was calculated analytically by applying one-dimensional diffusion model considering the base metal dissolution, thereby equations were derived for estimating the concentration Ct of aluminum, titanium and chromium. The calculated values corresponded well with the experimental ones, except in the early stage of homogenizing process. It follows that the equation by applying one-dimensional diffusion model can estimate the holding time for completion of homogenizing process in fabrication.
This study investigated the effects of bonding conditions on the mechanical properties at 1255K of Transient Liquid Insert Metal Diffusion Bonding (TLIM-bonding) joints of Ni-base superalloys, MM 007 with the commercial amorphous insert metals such as MBF-30, MBF-80 and MBF-90. The bonding conditions, viz., the bonding temperature, the bonding atmosphere and the homogenizing atmosphere were varied. The bonding temperature didn't affect the tensile property of the TLIM-bonding joint, but the bonding atmosphere and the homogenizing atmosphere affected it, viz., the tensile strength of the bonding joint was approximately equal to that of base metal at the bonding atmosphere of 13.3 mPa and at the homogenizing atmosphere of 6.7 mPa. Moreover, the tensile strength scattered without using the bonding spacer. It can be concluded by the detailed observation of the fractured surfaces of the bonding joints that the tensile strength lowered by forming the flat and brittle fractured surface due to the oxide film on the surface of base metal.
The Ni50-Ti50 type of shape memory alloy is welded using friction welding process under several upset force conditions. When friction welded joints were heat treated, joints showed the good mechanical properties and shape memory characteristics, because friction welding process gave severe hot deformation in welded zone during joining process. This heavy deformation made fine micro-structures and this was preferable effect on shape memory characteristics. It clearly shows that the all welded joints has almost same transformation temperatures to base metal after heat treated condition. The stress strain curves shows the better shape memory tendencies than base metal.
The final properties of our study is to discuss the selection of surface modification processes and/or materials from a viewpoint of blast erosion properties. In this study, an experimental investigation was carried out on the blast erosion resistance of sintered ceramics and ceramic sprayed coatings. Three different coatings of WC-12Co, Al2O3 and Cr2O3, which were produced by FLSP and PSP, were examined in comparison with the sintered ceramics. The effect of test conditions, such as blast angle and blast particle size, on the erosion resistance were made clear. The better correlation between volume erosion rate and Vickers hardness after erosion could not be obtained from the experimental results. It appears that the blast erosion properties of sintered ceramics and ceramic sprayed coatings may be affected by not only the hardness but also the fracture toughness. It was also confirmed by experiments that the material (process) selection could be easily conducted using the relationship of the erosion resistance between the blast angle 30° and 90°. It made clear that the effect of blast angle on the volume erosion rate of the sintered ceramics and sprayed coatings could be approximately estimated by the assumption of sinΨ (Ψ: blast angle) dependency.
In welding fabrication of heavy electrical sections which are composed of thick plates and are not mass-produced, ti is not so easy to utilize industrial arc welding robots because of taking a long time for teaching weld lines and welding parameters. It is necessary to simplify teaching operations so that a industrial arc welding robots may be applied to wedling of heary electrical sections. The welding program for multi-pass wedling, which is able to set up the welding parameters for various welding positions (flat, vertical and horizontal) and groove shape of Joints (fillet, single bevel, V, J etc.), has been developed. This multi-pass welding program was built in arc welding robots system and applied to welding fabrication of heavy electrical sections. With this system, the optimum parameters and wire tip positions are set automatically only by inputting welding position, groove shape and its size after teaching the weld line of first pass. As a resultl the efficiency was greatly improved.
A two dimensional solidification modelling of cellular dendritic growth was proposed in order to study the weld solidification phenomena of stainless steels. The modelling was made based on the quenched solidification microstructures. Fraction solid with temperature and segregations of the solutes within the cellular dendrite were calculated by means of finite difference method. Main conclusions obtained are as follows: (1) In this modelling, fraction solid was increased very rapidly just below liquidus temperature, and thus the temperature where the beginning of solid bridge was formed was very close to the liquidus temperature. Therefore, the temperature range where the residual liquid was confined by the sllid bridges was very long. (2) These behaviors mentioned in (I) were fitted well with the actual solidification microstructures revealed by liquid-tin quenching. On the other hand, the parabolic growth model where solid-liquid interface advances in proportion to square root of time did not fit with the actual microstructure. (3) Distributions of Ni and Cr in cellular dendrite calculated corresponded well to the EPMA results. (4) It was concluded that the two dimensional modelling proposed in this reoprt was very useful to understand the weld solidification phenomena.
Two dimensional modelling of the cellular dendritic growth during weld solidification was applied to the prediction of Solidification Brittleness Temperature Range (BTR) of several kinds of stainless steels. The calculation of BTR was done based on the observation that the lower temperature limit of BTR corresponded to the temperature at which residual liquid enriched with impurities solidified completely. This treatment gave a good agreement between the calculated and the experimental BTR for ferritic and fully austenitic stainless steel by paying attention to mesh size in the model. Moreover, the treatment was also useful to rank harmful elements in crack susceptibility. Then the modelling was applied to the prediction of the reason why duplex stainless steel had a relatively large BTR. As the results of this calculation, it was judged that nitrogen was very harmful element. This prediction was confirmed experimentally by making the tentative deposited metals containing low nitrogen. Therefore, the calculation proposed was considered to be very useful to predict or analyze BTR for materials which solidified as single phase.
Weld solidification crack susceptibility and pitting corrosion resistance of tentative duplex stainless steels were investigated in order to decrease the crack susceptibility without decreasing the corrosion resistance in a duplex stainless steel. The results obtained are as follows: (1) Crack susceptibility was improved with decreasing the N content in 22 to 25Cr-1 to 10Ni duplex stainless steels, but was not considerably changed with increasing the Mo content up to 4.5% at constant level of 0.03%N. (2) Corrosion resistance was improved with increasing the Mo content at constant level of 0.03%N. As a result, it was suggested that a lower N and Mo in the range of 4.0 to 4.5% were very effective for the development of a duplex stainless steel which had the low crack susceptibility without decreasing the corrosion resistance.
Microstructures of stainless steels rapidly solidified by laser surface melting (LSM) were investigated. In addition to the massively solidified structure and the rod-like eutectic structure which have been reported, characteristic structures, named as film-like ferrite, and rod-like ferrite were observed in LSM treated specimen. TEM and STEM analysis have revealed that there was not specific orientation relationship like K-S relationship between rod-like ferrite and austenite matrix, while there was K-S orientation relationship between film-like ferrite and austenitee matrix. Between ferrite and austenite matrix in vermicular ferrite structuer 4 or 5 degree deviation from K-S orientation direction had been observed. Segregation of elements due to solid transformation from ferrite to austenite was observed in vermicular ferrite and film-like ferrite structures, but no segregation due to solid transformation was observed in rod-like ferrite structure. From these results it was deduced that: (1) as for vermicular ferrite structure, delta ferrite is the primary phase of solidification, and austenite solidifies at the terminal stage on solidification and a diffusional solid transformation from ferrite to austenite takes place. (2) as for film-like ferrite, delta ferrite is dominant phase of solidification and a diffusional solid transformation follows with drop temperature than that of vermicular ferrite structure. (3) as for rod-like ferrite, LSM treated specimen solidifies completely to ferrite and a massive (patitionless) solid transformation from ferrite to austenite takes place during cooling.
A series of Fe-Cr-Ni ternary alloys were surface-treated by laser beam at four traveling velocities and an investigation was carried out to determine the effect of rapid solidification on the microstructures and ferrite content of laser surface-treated alloys. The cooling rates in laser surface-treated alloys were estimated to be 1.9×103K/s-2×105K/s by cell size. It was found that the variation of ferrite content with increasing cooling rate could be categorized into five types. The first one was that ferrite content was always 0% and did not change with cooling rate. The second one was that ferrite content decreases with increasing cooling rate, and this was corresponding to the change in solidification mode from primary austenite to full austenite or from primary ferrite to massive solidification. The third one was that ferrite content increases with increasing cooling rate, as for this type it was found that solidification mode was always fully ferritic while solid state transformation after solidification was suppressed. The fourth one was that ferrite content first increased and then decreased with increasing cooling rate. TIG weld metal of this type solidifyed in form of primary ferrite and solid state transformation from ferrite to austenite occured during cooling, but in the laser surface treated specimen alloy solidifyed in form of the rod-like eutectic and no solid state transformation occured, so ferrite content increased a little. When cooling rate became larger than the critical cooling rate, solidification mode changed to the massive solidification and ferrite content decreased. The last one was that ferrite content was always 100% and did not vary with cooling rate. From these results it can be said that it is necessary to modify the Schaeffler diagram for rapid solidification process. So in present study the ferrite content in all specimens surface-treated by laser beam were measured and modified Schaeffler diagarams for four different cooling rates were given. By analysis of these data, the experimental formula to estimate ferrite line in the modified Schaef ler diagram for any cooling rate was presentated.
In the previous report, it was shown that the massively solidified structure and the rod-like eutectic structure formed when stainless steels of a certain composition range have been rapidly solidified using laser surface melting technique. It was also found by the formation of these structures a homogenization of element distribution and refinement of structure could be obtained. In the present study, the corrosion resistance of stainless steels with the massively solidified structure and the rod-like eutectic structure which was formed by laser surface melting was investigated. Corrosion resistance was evaluated by the passivation current density (Icrit) and Piitting potential (V'C100). It was found that the corrosion resistance of stainless steels was markedly improved by formation of massively solidified structure or the rod-like eutectic structure. SEM observation revealed that such improvement was considered to be attributed to the alleviation of the solidification segregation and refinement of structure in the massively solidified structure, and to be mainly attributed to the increase of interface area due to formation of fine two-phase structure in the rod-like eutectic structure.
Effect of rapid solidification by laser surface melting on pitting corrosion resistance in weld metals of Mo containing stainless steels was investigated. Pitting corrosion resistance was evaluated through the pitting potential and the density of pits after FeCl3 solution immersion test. The pitting resistance in the weld metal was shown to deteriorate severely in comparison with that in the base metal, whereas, with laser melting treatment, to be improved to about the same level or slightly better than that of the base metal. SEM observation revealed that pits which had preferencially formed at the core of the solidification cell in the weld metal, had reduced in number and also in size after laser treatment. The element distribution across the solidification cell was found to become more even in the laser treated weld metal than non-treated one. On the basis of the results, the improvement of pitting corrosion resistance in the weld metal by laser treatment was considered to be attributed to the alleviation of the segregation due to the rapid solidification effect which caused the increase of Mo and Cr contents at the cell core, resulting in the enhancement of its corrosion resistance.
The effect of cooling rate and impure gas on microstructure in Ti-6Al-4V weld metals was studied. The width and length of columnar prior-β grain of weld metal definitely depended on both the cooling rate during solidification and the prior-β grain size in HAZ. The microstructures within prior-β grain strongly depended on the cooling rate below β-transus. The weld metal consisted of α', α and β phases on smaller cooling rate, and only α' phase on larger cooling rate. The microsegregations during solidification readily decreased at very early stage of the weld cooling. Consequently, the distribution profiles of solute elements in the weld metal is due to the element partition during transformation from β to α' and α on weld cooling. When some amount of nitrogen or oxygen was added through the shielding gas on GTAW process, it was found that the enrichment of Al, and Fe, and the depletion of N or O took place at dendritic boundaries during solidification. These weld metals exhibited stable lamellar dual-microstructures of α and β phases, where depleted Al, V, and Fe. enriched N or O in α-phase, vice versa in another.
Susceptibility to weld solidification cracking of three kinds of Ti-alloys was investigated by Trans-Varestraint test. Weld crackings did not occur in Ti-6Al-4V at all, but significantly occurred in Ti-6Al-6V-2Sn and Ti-15V-3Al-3Cr-3Sn. Ti-15V-3Al-3Cr-3Sn was actually the most susceptible to cracking. Through close examination of weld solidification microstructures by tin-quenching, conspicuous segregations of V, Cr, Cu and Fe were confirmed at dendritic grain boundaries during solidification in each alloy The diffusion rate of solute elements in Ti-6A1-6V-2Sn and Ti- I5V-3A1-3Cr-3Sn was I order smaller than that in Ti-6Al-4V. Consequently, the amount of compositional microsegregation at dendritic boundaries in the former alloys was larger, because the effect of solid diffusion during solidification was smaller. In Ti-6Al-4V, these microsegregations were readily decreased and eliminated by the occurrence of solute diffusion at very early stage of weld cooling, while that in the other alloys remained till rather lower temperature to cause crackings due to liquid films of low-melting constituents.
Weld solidification was systematically investigated in Cr-Ni-Fe-Mo alloys. Emphasis was placed on the microsegregation of solute elements and the precipitation of intermetallic phases during solidification. Increased Ni content was found to reduce the extent of the segregation of Cr and Mo in the austenitic solidification. The precipitation of intermetallic phases was obvious at the welds with high Mo, Nb and Si content, but was suppressed by the increase of Ni content and the addition of nitrogen. The results obtained were compared with phase diagrams by Themo Calc to understand the equilibrium aspects of the solidification of these alloy welds.
The authors have treated hardenability in this paper in welding of medium and high carbon machine structural steels without and with Cr, Mo and Ni low alloy elements using Gleeble machine. Then a new equation for estimating HAZ hardness is introduced, using the concept of Δt8/3 parameter and carbon equivalent. Moreover, the new equation has been confirmed for the reliability by many data measured. Therefore, the estimation for HAZ hardness is possible for the steels whose carbon content is more than 0.3%.
Corrosion resistant alloy welds for seawater applications are necessary to be over-alloyed with Cr, Mo and nitrogen to have an increased Pitting Index value. The desired weld chemistry also requires less microsegregation of Cr and Mo and precipitation free microstruciure not only for higher corrosion resistance but also for good mechanical properties and weld hot-cracking resistance. Based on such requisites for the welds, nitrogen-added Ni-based filler metal, 22Cr-60Ni-9Mo-0.1N, was developed for the welding of a 6%Mo superaustenitic stainless steel. The weldment by the newly developed filler metal showed excellent chloride corrosion resistance comparable to the base metal. The weld solidification and microstructure were fully austenitic without any other phases and brittle precipitates in the whole weld. Thereby, the weldment also offered good ductility, toughness and hot-cracking resistance superior to the weldment by the conventional Alloy 625 filler metal.
In the previous report it was proved that the stress releasement mainly occured by transformation superplasticity compared with by transformation expansion under some conditions. For example one of conditions is the case that the much amount of thermal stress is generated in spite of a small transformed area. In the present study, in order to obtain the suitable conditions which make most use of the stress releasement in welding by transformation superplasticity, the transformation temperature was remarked. Since the transformation temperature changes by the kind and content of alloying elements, the steels with many kinds of transformation temperature were made and the effect of transformation temperature on stress releasement was investigated by use of a special torsion thermal cycle test apparatus. The results are shown as follows; 1) In the region of 4-14%Cr and 3.5-14%Ni in this study, the transformation start temperature (that is a martensite transformation) of the test steel is in proportion to the alloy contents. Martensite start temperature was shown as follows: Ms(°C)=719-26.5×Nieq(%)-23.7×Creq(%) Nieq=30×C+Ni+0.5×Mn, Creq=Cr+Mo+1.5×Si+0.5×Nb (unit: mass%) 2) The deformation stress in the midst of cooling took the minimum value at the temperature 70-80 degrees lower than its transformation start temperature. 3) According to the selected test materials having nearly the same transformation temperature and different chemical compositions, their deformation stress-temperature curves showed a similar characteristic. 4) From the results of 1) and 3) the change of deformation stress during cooling can be estimated from its chemical composition.
Selecting the tensile pin test from among the test procedures for evaluating the adhesive strength of sprayed coatings, the authors devised an adhesive strength evaluation technique. The results obtained are summarized as follows; 1) The fracture net stress (σnet)cr obtained by the pin test is influenced by the coating thickness and pin diameter, and thus dose not necessarily use as an index of the adhesive strength. 2) In the vicinity of the coating edge of the pin test, the stress σy in load direction is inversely proportional to the square root of the distance x from the coating edge to the center of pin. This stress singularity is expressed as follows; σy= κ/√x = FI×σnet/√x in which κ is an index representing the size of the field of singular stress. 3) The pin test results, when sorted out using the stress singularity parameter kcr universal values were given regardless of changes in coating thickness and pin diameter, suggesting that employing kcr enables the adhesive strength to be quantitatively evaluated.
It is well-known that hardenability of HAZ is one of the important factors for estimating weldability of steels. Therefore the parameter of cooling time from 800 to 500°C (Δt8/5) has been usually used for estimation of the hardenability of lower carbon high strength steels. However it is not clear if for higher carbon steels Δt8/5 is also useful parameter for the estimation, because the Ms temperature of these steels is lower than usual lower carbon steels. For this purpose this paper has investigated the usefulness of application of Δt8/5 parameter for the HAZ of higher carbon steels. Conclusively, it was cleared that the Δt8/3 parameter is better than Δt8/5 for these steels. Then the authors have introduced a new equation for estimation of the HAZ hardness for higher carbon steels. using Δt8/3 parameter.