The dismantling of the pressure vessels for the commercial atomic reactor is now planning in the world and for the dismantling, underwater cutting is a good method shielding the operators and the reactor-site from the induced radiation. These pressure vessels of the commercial atomic reactors were made of 150-250 mm thick carbon steel with 18-8 type stainless steel of 6-12 mm thick cladding and the underwater cutting have to carried out from stainless side. The report is concerning underwater derwater gouging of the stainless steel clad to underwater gas outting of the stainless clad steel used for the commercial pressure vessels. Underwater gouging is a process that the stainless steel clad is melted by arc heat which is generated between a mild steel wire or strip as a electrode and the stainless steel as a work, and blown out by jetting water from a rear nozzle. Continuous gouging can be done by means of travelling a carriage automatically. Gouging current flown discontinuously at gouging speed of 15-20 cm/min, but satisfactory gouging which was achieved pretty gas cutting was obtained.
An arc welding method has been. developed in which welding current is switched alternately to each electrodes of TIG and MIG welding methods to prevent the arc interaction between the two electrodes. This method is hereinafter referred as switching TIG-MIG welding method. In this method, the polarity of the tungsten electrode of TIG is negative to eliminate the consumption of the electrode and the polarity of the feeding wire of MIG is positive to increase melting of the feeding wire. In observing the arc phenomena of this method, authors clarify that stable arcs without any interactions between the two electrodes are maintained by feeding the welding currents switched by transistor curcuits in a frequency of about 200 Hz. Furthermore, the feeding wire is easily melted at the tip and the droplets of the weld metal are periodically removed from the top of the wire without spattering due to exposing the. feeding wire in thee arc of TIG. In this welding method, since the welding currents of TIG and MIG are able to change independently to each other, the feeding wire of MIG can feed without varing the heat input complementing insufficient welding current to penetrate the base metal by the heat input of TIG.
In order to obtain fundamental data for control of weld penetration depth in election beam welding, responsibility of the depth to the variation in the beam current and its limit value were investigated. In the experiments, linear current. variations with time were selected for easy analysis of the experimental results. Results are summarized as follows: 1) Response of the depth to increase of the beam current is worse than that to decrease. Especially, under the conditions of lower welding speed and larger beam diameter, that is, when more amount of molten metal exists, the difference in both responsibilities becomes more remarkable. 2) When a focused beam is adopted, the depth varies proportionally to the beam current in the range less than 500 mA/sec. 3) When the beam current pulsates across a DC value, the limit of pulsation of the depth in the macroscopic view is fr, that is, the characteristic frequency of the intermittent melting process of the electron beam as described in the previous report. 4) From the results above mentioned, spike phenomenon in the root of penetration could be suppressed by control of electron beam current keeping the macroscopic shape of fusion zone constant.
Pure iron was welded in a controlled arc atmosphere. Effects of the welding conditions and the oxygen partial pressure in Ar-O2 welding atmosphere on the oxygen content of iron weld metal were systematically studied. The results are summarized as follows: 1. The temperature of iron molten pool is measured by using a thermocouple. According to the result, the temperature is suggested to be above 1600°C-1680°C. 2. The oxygen content of iron weld metal decreases with increasing welding current and increases with increasing arc voltage (PO2=0.03 atm). 3. The oxygen content of iron weld metal increases with increasing of partial pressure of oxygen under low partial pressure of oxygen in Ar-O2 welding atmosphere. However the oxygen content becomes a constant value of about 0.24 wt.% under high partial pressure of oxygen. 4. The oxygen content of weld metal is higher under electrode negative (DCRP) condition than under electrode positive (DCSP) condition. 5. Behaviour of oxygen absorption into iron weld metal is discussed by using equilibrium data.
In order to study on fatigue crack growth characteristics at the toe of fillet welded joints, simple plate type specimens with fillet welded gussets were tested under load controlled conditions by T- and 4-point-bending. Fatigue crack growth tests on edge-notched and planer surface notched specimens were also carried out under plane bending load. The results are summarized as follows: (1). Fatigue crack growth behaviors along the weld toe lines were affected by bending stress range, Δσb and stress concentration factor at the weld toe, Kt, but to depth direction not so much affected by the variation of Δσb. (2). The average crack growth rates along the weld toes in earlier stage of life may be expressed as, d(2b)/dN=C(Kt⋅Δσb⋅f1(R))m here, f1(R): Coefficients of stress ratio R, 1.0 for R=0 and 0.614 for R=-1; C, m: Material constants. The values of f1(R), C and m to be used were derived from the test results of surface notched specimens. (3). The crack growth rates to depth direction may be expressed. as, da/dN=C⋅f(R)⋅(ΔK)m here, f(R): Coefficients of stress ratio R, 1.0 for R=0 and 0.5 for R=-1. ΔK: Range of stress intensity factor in a plate with edge crack under uniform bending. C, m: Material constants derived from the test results of edge notched specimens.
The development of GMA welding (D.C.R.P.) for 9%Ni-Steel with similarly composed nickel alloy wire through the study on the instability of welding arc based on the aspects of cathode spots movement is described. Under the condition of open arc in Ar atmosphere with constant current characteristic power supply, cathode spots move erratically and irregularly on the plate surface in front of weld pool, and it results in unstable welding arc. The addition of oxygen to Ar shielding gas causes the concentration of cathode spots in the narrow region right under arc column, and the increase in melting efficiency of base metal and in oxygen content in weld metal. On the other hand, under the condition of buried arc in He atmosphere with constant potential characteristic power supply, the arc root is confined within the well of weld pool and fairly good weld metal for 9%Ni-Steel with similarly composed nickel alloy wire is obtained. Very small blow holes are apt to appear at the root of fuzed zone in this case, but they are effectively decreased by applying a fast transverse weaving method to buried arc.
Studies of mechanical properties of steels subjected to thermal prestraining cycles have been presented as valuable experimental works for discussion of weld joint strength. It is noted here that if mechanical properties of steels subjected to thermal prestraining cycles can be denoted as a function of the Vickers hardness, then it is easy to determine material constant and analyze the deformation behavior of weld joint from the view of heterogeneity. Three kinds of steels, a carbon steel (SM41B), an austenitic stainless steel (SUS304) and a martensitic stainless cast steel (SCS5) were used for experiments. The mechanical properties depend upon thermal prestraining conditions, especially peak temperature. For example, as the peak temperature is higher yield stress increases and also Vickers hardness increases. The experimental results indicate that elastic limit, yield stress, strength coefficient and strain hardening exponent of steels subjected to thermal prestraining cycles can be expressed as a function of Vickers hardness. As an application, material constants for elastic-plastic FEM analysis can be determine from the Vickers hardness distribution of weld joint and in this paper weld joint with poor penetration is analyzed in terms of path independent J-integral, crack opening displacement (COD) and plastic zone extension.
In order to detect precisely internal flaws at boundary surface of clad plates, ultrasonic testing with scanning device and focusing type probe are carried out on two subjects. First, the tests are made for various forms and dimensions of hole defects artifically drilled within test pieces, and accuracy and sensitivity of measurement and effects of flaw size and position on the echo pattern are evaluated. Secondary, the scanning tests are applied for explosively welded Al alloy- or mild steel-clad steel plates, and the areas of interfaces are finely inspected, the results of which are confirmed by microscopic examination on the sections of the plates. A summary of the results is shown below. When the focus of ultrasonic beam probe coincides with flaw position, it is possible to detect seperately two adjacent flaw 1 mm away, and the sensitivity depends upon the focal diameter. Delayed echo, however, occurs when two flaws are too close together or the focus shifts from flaw position. The detectable depth of internal flaws depends upon the diameter and focal length of probe, and becomes deep-er with increasing focal length and diameter. There are three types of flaw echo for boundary surface of clad plate, that is, lower wave-shaped, higher wave-shaped, and flat-shaped patterns reflected at interspersed flaws, large defect with interspersed flaws, and unwelded interface respectively.