Fe-Cr and Fe-Ni alloy sheets were welded by gas tungsten arc welding in an arc atmosphere-controlled chamber filled with argon-nitrogen gas mixtures in order to stduy effects of chromium and nickel on the nitrogen absorption of iron alloy weld metal. In Fe-Cr alloys, the nitrogen content of weld metal decreases with increasing the welding current. In Fe-Ni alloys, the nitrogen content of weld metal hardly depends on the welding current. In each alloy, the nitrogen content of weld metal increases with the nitrogen partial pressure of the atmosphere in low nitrogen partial pressure region, and is constant in nitrogen partial pressure more than 0.01MPa. The nitrogen content of weld metal increases remarkably with the chromium content, while decreases slightly with increasing the nickel content. The nitrogen absorption of iron alloy weld metals was discussed thermodynamically by comparing with data of arc-melting and equilibrium.
We have developed a new pressure joining process of Al-Cu pipe joints utilizing an eutectic reaction as reported in a previous paper. In this report, the process has been applied for joining Al to Al by using insert foils at the joining interface. Al-Si hyper-eutectic alloy foils solidified rapidly from the melt was found to have an excellent bondability even in air. Joints with high mechanical properties comparable to those of Al base metal can be obtained under the following conditions: 1) Si contents in the Al-Si alloy foils are above 20 wt% 2) joining pressures are above 19.6MPa. The reason for being able to join successfully in air is considered that Al surface layers are melted and cleaned by the reaction between the Si of hyper-eutectic composition and Al.
The purpose of this study is to investigate the influence of oxygen on the weldability of the joints between aluminum bronze and austenitic stainless steel. Bondings were performed using Cu foils with different oxygen content. Different aluminum bronzes with various aluminum content were also used. The tensile strength of joints decreased rapidly as the oxygen content in Cu foils increased. The joint efficiency decreased as the aluminum content in aluminum bronez increased. When the oxygen content was low up to 28 ppm, the aluminum content in aluminum bronze did not affect its strength. The segregation of aluminum and oxygen on the surface of the aluminum bronze was recognized by AUGER analysis. From the results of this analysis, aluminum oxides are considered to be formed on the surface of the aluminum bronze. The weldability of the joints lowed when the higher oxygen content Cu foils were used, but the tensile strength of the joints increased when the surface of the aluminum bronze before bonding was sputtered by Ar-ions first and then coated by Cu.
The possibility of the welding of amorphous metal foils was examined. Fe78Si9B13 amorphous metal foil having 20 microns in thickness was welded by using a stored energy type spot welding machine. This foil was possible to weld without crystallization at a welding time within 0.4 milliseconds. The irregularity of weld nugget shape was due to the unevenness of the foil surfaces employed. This resulted in the scattering of tensile-shear strength of single spot welds. Increasing weld time with the use of the capacitor bank having excessive capacitance led to a brittle weld nugget, though crystallization did not occur. In tension-shear test, a crack initiated near the periphery of the weld nugget and propagated in the base metal. It means that the enhancement of joint strength was difficult by multiple spot welding.
Temperature at the joint interface is able to be measured by detecting the voltage between copper alloy lead and thick film on alumina substrate in micro-soldering process. Temperature at the interface of soldered joint is very important quantity for quality of soldered joint. But it is too difficult to measure the temperarture at the interface of micro-soldered joint, because of its size being too small. It is found that the voltage occurs between copper alloy lead and thick film on substrate during reflow soldering process using heated tip and, furthermore, it is shown that the voltage is proportional to the temperature at soldered interface of the joint. As a result, the temperature of the joint interface of can be easely measured by detecting the voltage between lead and thick film during micro-soldering process.
Monitoring of the quality of soldered joint is researched and developed by detecting the voltage between copper alloy lead and thick film on the substrate in micro reflow soldering process with heated tip with controlled current. Quality of soldered joint, which is composed with copper alloy lead (Cu-Sn) and thick film (Ag/Pd or Ag/Pt: thickness 10 μm) on alumina substrate or porceline substrate, is mainly influenced by the temperature at soldered part, heating time in micro-soldering process and tip force. Furthermore, the quality of joint confirmes by being approximately estimated soldered area by tensile shear testing or peel testing. The quality of soldered joint is shown experimentally to be estimated to some extent by the measurement the effective integral of the voltage between copper alloy lead and thick film on the substrate in micro-soldering process.
Radial heat flux distribution of plasma arc on a surface of cutting plate influences not only on the cutting groove shape but also on the maximum cut thickness. No available technique, however, have been realized to estimate the radial heat flux distribution in cutting groove until now. So, a new technique was developed for measuring the radial heat flux distribution in the cutting groove with two information on cutting front shape and position of the plasma arc, since the required heat flux to melt the cutting front balances with the heat flux from arc to the cutting front. Each arc position in the groove was measured with snapshots of the arc and the cutting front. The required heat flux value was estimated by a numerical calculation with a least squares-collocation method on the cutting boundary, which belongs to the Method of We ghted Residuals (MWR). A set of functions derived by separation of variable for the two-dimensional heat conduction equation in quasi-stationary state was selected for trial functions in the MWR, which satisfies the differential equation and boundary conditions except those on the cutting front and side surface. Following results are clarified by the new technique; 1) Heat flux distribution on the cutting front can be estimated by using the new technique even though wide unknown regoin of boundary condition exists near solidifying line of cut surface. 2) The degree of symmetry of radial heat flux distribution in plasma arc cutting groove scarcely changes in comparison with that in free boundary condition. 3) Values of melting efficiency in ordinary plasma arc cutting pretty differs from those in moving line heat source model.
Thermal cycling and thermal shock tests of Zirconia thermal barrier coatings deposited to structural steel substrate were carried out. Finite element analysis of thermal stress was also carried out. The number of thermal cycles to failure was reduced with increasing in test temperature. The number of thermal cycles to failure increased with an increase in specimen width and by introducing the bond coatings. The oxidation of substrate and the tensile thermal stress overlapped to occur the adhesive failure at the interface during thermal cycling. The heating rate and the holding interval seemed to be the important factors to influence the failure life in the thermal shock test, while the cooling condition was not so relevant in the present case of the adhesive failure at the interface due to the oxidation and the thermal stress.
In this report, isothermal solidification process on transient liquid phase insert metal diffusion bonding of Ni-B binary system and Ni-P binary system was investigated. From experimental results on the isothermal solidification process, it was clarified that this process was controlled by the diffusional process of B and P in the base metal. The activation energy Q and frequency factor Do for diffusion of B and P in Ni obtained were as follows B in Ni: Q=226 kJ/mol, Do=0.14 m2/s P in Ni: Q=284 kJ/mol, Do=0.49 m2/s The complete time of the process can be estimated by equation (1) and (2) Ni-B system: t1/2f=53.8×(2h/D1/2)…………(1) Ni-P system: t1/2f=26.4×(2h/D1/2)…………(2) The isothermal solidification process on Ni base superalloy joints were also examined. The isothermal solidification process of MM-007, MarM-247, Inconel-713C and Inconel-600 joints with using Ni-15.5%Cr-3.7%B insert metal can be also interpreted by the same theoretical equation applied to the process of Ni-B system.
The previous paper revealed that quenching crack type cold cracking in HAZ of medium/high carbon low alloy steels can be suppressed by the reduction of hardness and phosphorus, which are the main influencing factors on the cracking. Therefore, in this paper, the changes in hardness, intergranular fracture surface and fracture stress under the various cooling conditions have been studied in detail by the simulated cold cracking test. From the results of this investigation, a criterion has been proposed to prevent this type of cold cracking. The fracture stress has an excellent correlation with the area fraction of intergranular fracture surface. The fracture stress giving little intergranular fracture surfece is more than about 950 MPa. The hardness has also a good correlation with the area fraction of intergranular fracture surface. The hardness giving little intergranular fracture surface is less than about Hv600. The area fraction of intergranular fracture surface within Hv600 to 700 is largely influenced by cooling rate, i.e. that is fairly low at lower cooling rate, although the hardness is nearly the same compared with the higher cooling rate. Therefore, there is a good correlation between hardness and fracture stress; however, within Hv600 to 700, the fracture stress is fairly high at lower cooling rate because of the effect of cooling rate due to the relation of the hardness and the area fraction of the intergranular fracture surface. By adoption of the condition of the hardness less than about Hv600 or fracture stress more than about 950 MPa, it was thought that quenching crack type cold cracking is avoidable.
The effect of preheating on quenching crack type cold cracking in HAZ of JIS SNCM439 and SK5 has been studied by the y-slit cracking test utilizing GTA welding with duplex stainless filler wire without the effect of diffusible hydrogen. Furthermore, the validity of the crack free condition which was proposed in the previous paper by the simulated cold cracking test under the various materials and cooling conditions has been also studied by use of the results of the y-slit cracking test. In SNCM439, it was noted that cracking do not occur at somewhat low preheating temperature, although the hardness and microstructure (martensite with some retained austenite) are nearly the same as that of without preheating. Therefore, it was found that cracking in this steel can be avoidable by adoption of lower preheating even in the range of cooling rate without bainite. In SK5, cracking has a tendency to decrease gradually with decreasing in hardness through the increase in formation of troostite and bainite by increasing preheating temperature. According to the crack free condition of the hardness less than about Hv600 or the fracture stress more than about 950 MPa suggested in the previous paper, it was confirmed that cracking do not occur under the condition of the restraint intensity 15 kN/mm⋅mm in the y-slit cracking test. Consequently by use of the relationship between the hardness and the fracture stress, the critical hardness in HAZ for cracking can be easily estimated for various restraint intensities in actual weldedjoint.
Solidification sequence of austenitic stainless steels, SUS31OS, SUS316L and SUS304L, was investigated by freezing the solidification microstructure with liquid-tin quenching during GTA welding. The results are as follows: (1) Liquid-tin quenching method had sufficient cooling rate to reveal the solidification sequence, even though the weld metal solidified with the primary ferrite and the subsequent austenite. (2) The solidification microstructure of SUS310S, which solidified with only austenite, can be evidently observed within Solidification Brittleness Temperature Range. Liquid droplets were confined to the intersectional site of the primary and the secondary dendrite arm boundaries due to formation of a solid bridge near the solidification front. (3) In SUS316L which solidified with the primary austenite, the subsequent ferrite formed from the same confined liquid during solidification as mentioned in (2). In the case of SUS316L which solidified with the primary ferrite, on the contrary, the subsequent austenite formed from the liquid remaining between primary ferrites. Residual liquid was found at the austenite/ferrite interphases. (4) SUS304L solidified with the primary ferrite and the subsequent austenite formed at. cellular dendritic boundaries. Residual liquid was found at the center of the austenite. With the obtained results, solidification sequence of each austenitic stainless steel during solidification could be illustrated in a more detailed fashion.
Solidification sequence of ferritic and duplex stainless steels was investigated by freezing the solidification microstructure with liquid-tin quenching during GTA welding. The features of solidification sequence observed are as follows: (1) A solid bridge formed at very high temperature near the solidification front due to the mutual contact with tips of adjacent secondary dendrite arms. (2) Residual liquid droplets were confined to the intersectional site of the primary and the secondary dendrite arm boundaries. (3) In the weld metal which solidified with only ferrite, cellular dendrites were rapidly obscured as temperature decreases even within Solidification Brittleness Temperature Range. Especially, the obsculation of the secondary dendrite arm boundary was much easier than the primary dendrite arm boundary. These features can not be explained by the application of the unidirectional solidification model.
This experiment is attempted to find corrosion resistance improvements by Laser beam surfacing. The AISI 304 type stainless steel welds were surfaced by a 2 kW CO2 Laser beam under several conditions. Laser surfaced specimens were evaluated under acidic corrosion tests and some metallurgical observations. This revealed that Laser surfacing resulted the changes in morphology of carbide precipitations in the HAZ of MIG welded joints. Following results were obtained from a series of experiments. 1) The MIG welded joints of AISI 304 type austenitic stainless are able to recover from the weld decay using Laser beam surfacing. 2) It is considered as the conditions for optimum Laser scanning being the partially melted ones. This case gave a 0.25 mm depth of solid solution treatment.
Pulse arc welding has superior characteristics on arc stability and refining of micro-structure of weld metal. This experiment was carried out to clarify the influence of pulse welding current on solidification cracking tendency of austenitic stainless steel weld metal under low pulse frequency. Experimental results were as follows; Pulse welding current makes finer columnar structure and decreases segregation of sulfur and phosphor in weld metal. From these reasons, solidification crack in austenitic stainless steel weld metal is decreased using pulse welding current.
Soft weld joints or under matching weld joints are often employed in the welding of high tensile strength steel to avoid crackings. The compressive strength of structural members, such as columns, plates and pipes, with soft weld joints is analyzed by Finite Element Method and simple mechanical models. Especially, the effects of the width and the location of the soft joint, slenderness ratio, initial deflection and the strain hardening are clarified.
The fatigue crack propagation properties were investigated in six types of steels for welded structures, those yield strengths range from 163 to 888 MPa. The effect of stress ratio R and material properties, such as yield strength or grain size, on the fatigue crack growth behavior can be traced on the crack clousre, and when the growth rates are plotted in terms of effective stress intensity factor range ΔKeff, the crack growth behavior of all steels at various R can be expressed by one curve. Then the resultant curve (da/dN-ΔKeff for all steels) can be available in the most conservative estimation of fatigue crack propagation in welded steel structures even under high tensile residual stress or high R. The crack closure is dependent on both R and ΔK, and the crack opening ratio for all steels can be expressed by the function of ΔK and R which has previously proposed by the authors. Namely, crack closure is remarkable only near threshold ΔKth for R≈O. Considering this dependence of crack closure on ΔK, the well-known relationship between Paris' coefficients C and m can be explained quantitatively. Moreover, the predicted variation in ΔKth with R using above-mentioned U equation shows good agreement with the experimental results. The ΔKth at R=0.1 decreased with increasing yield strength or decreasing grain size except for the steel with the lowest yield strength.
The effects of joint clearance on fatigue crack initiation life and crack growth rate of brazed joint were investigated. Tes tspecimens used were butt joint of carbon stcel and stainless steel brazed with pure copper with/without an artificial defect in joint. It was inferred from the fatigue test results that fatigue life of joint depend not on crack growth rate but on crack initiation time. From these test results and the theoretical investigations on the restraining effect of basemetals on plastic slip of filler metal and crack tip plastic deformation in joint, the mechanisms how joint clearance affects on fatigue life of brazed joint were made clear.
The authors proposed an off-line programming system which consisted of four levels of software modules hierarchically; i) task level, ii) tool level, iii) robot level, and iv) machine code level. This paper describes the generation of the trajectory for the weld torch on the work model at the tool level. The torch angles specified by the system user along each of weld lines is checked automatically by calculating intersections between planes of the work model and the check plane, which is an imaginary plane defined by the weld line and the axis of torch head. If an intersection beyond the weld line is detected, it is recognized that a corner obstacle is there, and the obstacle is avoided by tilting the torch head along the weld line. If the intersection can be avoided by rotating the check plane, it is recognized as a projection obstacle, and the torch angle is modified with the torch head in the rotated plane. If the intersection still exists, it is recognized as a bridge obstacle above the weld line. When the obstacle is near either end of the weld line, the bridge obstacle is avoided by inserting the torch head with tilting. Otherwise the weld line is divided into two segments at the center of the bridge area. The validity of the algorithm is confirmed using some sample objects with the motion simulation on display monitor.
Residual stress occurred in Si3N4 to metals joints were analyzed by thermal elastic-plastic finite element method. In order to investigate the effect of the bonded material to Si3N4 on residual stress, numerical analysis were conducted on the condition simulating Si3N4-Si3N4, W, Mo, Ta, Nb or Cr-Mo steel joints with the insert layer. Maximum principal stress occurred in Si3N4 was lowering in the order of Cr-Mo steel, Nb, Ta, Mo, W, Si3N4. Maximum principal stress in Si3N4 of Si3N4 to Cr-Mo steel joints decreased with increasing the insert layer thickess in the range up to about 1.0 mm thick. As diameter of specimen increased, maximum principal stress in Si3N4 increased. Maximum principal stress in Si3N4 of Si3N4 to Cr-Mo steel joints was reduced irrespective of diameter of specimen with an increase in the thickness of W being used as the interlayer.