JPH1034374A - Method for generating residual compressive stress in stainless steel and ni-based superalloy, and method for repairing stress corrosion crack by underwater welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart a residual stress to a molten part by melting underwater the surface of stainless steel or a Ni-based superalloy using a plasma arc welding torch (PTA torch) that is provided with a suitable water eliminating device, performing repair welding for cracks, and quenching in accordance with the movement of the torch. SOLUTION: A PTA torch 10 for underwater melting or welding is equipped with a conical or cylindrical water eliminating device 16 at the tip end of a gas lens 14; with the skirt of the device coming into contact with the surface 41 of a base material to be processed, the surrounding water is eliminated by a shield gas from an inactive gas supply line 11, enabling a local waterless area to be obtained forming a stable beam 42 and a molten metal pool 45. In addition, the body of the water eliminating device 16 is provided with minute and numerous holes for diffusing extra shield gas. With this torch 10 moved in the direction of the arrow 47, the surface 41 of the base material is continuously melted and cooled. Incidentally, as necessary, a welding material may be added to the molten pool 45.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to the field of residual tensile stress in stainless steel and nickel-base superalloys.
nsile stress) and residual compressive stress (residual
about increase in compressive stress). In another aspect,
The present invention relates to the prevention of damage caused by stress corrosion cracking, helium embrittlement and hot cracking of such alloys.
More specifically, the present invention relates to a conductive quench for promoting the generation of residual compressive stress to prevent crack damage in structures made of crack-prone alloys.
ing).

[0002]

BACKGROUND OF THE INVENTION Welding involves the localized heating of the joint of two parts to be joined, whereby the joint and the filler metal applied to the joint are filled.
l) causes local melting. The weld is obtained by solidification of this molten material. This local heating causes not only local melting, but also expansion of the metal adjacent the weld pool. Following this expansion, shrinkage occurs during cooling. The temperature gradients inherent in such welding operations lead to thermal stress gradients, which generate residual stresses. Such stress is called residual stress because it remains after the welding operation. Such stresses are intrinsic to the material being welded, in other words, no external traction is required. These stresses are present in the solidified weld metal and in the heat affected zone (HAZ) around the weld. In conventional welding, such residual stresses are generally tensile stresses in the weld and inside the HAZ. These generally become compressive at a distance from the weld, but the magnitude of such compressive stress is generally smaller than the magnitude of the tensile stress. The overall force must be balanced, which is achieved by balancing large local tensile stresses with compressive stresses that spread over a smaller but larger volume.

[0003] The magnitude and distribution of these residual stresses is determined by the heat applied to the weld, the geometry of the part being welded, and the heat transfer to the outside of the weld and the HAZ. The exact thermal gradient depends on the balance between the heat input by the weld and the rate at which that heat is removed. The boundary conditions considered in conventional welding assume that this heat is removed by conduction to the cold portion of the surrounding metal (ie, the portion of the material being welded away from the weld).

[0004] Relatively little heat is removed by radiation from the weld and the HAZ or conduction through the gas in contact with the outer surface of the weld and the HAZ. The invention disclosed in the present specification renews this so that a relatively large compressive residual stress is generated in the weld and the HAZ. This can be achieved by performing the welding in water or in some medium that can be used to quench the weld and the HAZ. In the present invention, water acts as a conductive medium that removes heat from the weld and the surface of the HAZ very efficiently. This modified heat flow results in the generation of compressive stresses in the weld and the HAZ. This is important, because of the generation of such compressive stress, there is a tendency for the weld and the HAZ to promote stress corrosion cracking after hot welding and helium cracking (He cracking) that develop when the weld cools or after welding work. Stress corrosion cracking that occurs when exposed to certain conditions.

[0005] Hot cracking is caused by a tensile stress acting on a weld during solidification. Welds generally do not solidify at a single, limited temperature. Solidification occurs over a range of temperatures, unless one deals with ultrapure single element or single compound materials. As solidification occurs, the shrinkage that evolves during solidification or shrinks due to the temperature drop causes the generation of stress. When such stress acts on the solidifying material, hot cracking occurs. This is because the existing liquid cannot support the tensile stress. Such cracks can be prevented if a compressive stress is generated instead of a tensile stress.

Helium embrittlement also occurs due to the action of tensile stress generated during cooling, and can be prevented if compressive stress is generated instead of tensile stress. Helium embrittlement results from the generation of internal He generated by nuclear irradiation. This phenomenon hinders the success of repair welding on irradiated materials. The generation of compressive stress allows such repairs. The generation of compressive residual stress is caused by stress corrosion crack (SCC).
king). As the name implies, stress corrosion cracking requires the action of stress, and residual stress is an important source of such stress. SCC occurs when the weld and the HAZ are exposed to a suitable medium after the welding operation.
By preventing the action of tensile stress in the presence of such a medium, stress corrosion cracking can be prevented. Therefore, if compressive stress is generated instead of tensile stress, SCC
Can be minimized.

[0007] It has now been found that plasma transfer arc welding repair of stress corrosion cracking damage in water exposed parts of nuclear reactors and similar equipment and structures can be achieved by performing an underwater welding process. This welding process involves setting requirements, forming a weld pool of molten metal, cooling the weld pool to form a metallurgical bond with adjacent unmelted parts, and welding to ambient temperatures below the melting range. Includes rapid cooling of parts. The weld pool can be formed from a compatible alloy filler metal supplied in powder or wire form, or can be formed spontaneously from the substrate to be repaired. By bringing the molten pool into contact with the surrounding water during cooling, it is possible to obtain heat flow characteristics that reduce tensile stress and promote generation of compressive stress.

[0008]

It is clear that a number of beneficial effects can be obtained by generating compressive rather than tensile stress, and the present invention produces such beneficial stresses.
Such stresses occur when welding operations are performed underwater using a local drainage system that keeps water out of the weld pool. As the welding torch moves, the weld is exposed from the local drainage device, but the weld has solidified by that time. Nevertheless, heat transfer from the weld and the HAZ is altered by placing the weld in water, which causes the generation of compressive stress.

[0009] Since the rejection device is pressurized to a pressure slightly above ambient pressure, such underwater welding can be performed at shallow or deep water. Beneficial effects can be obtained with or without filler metal. Conventional filler metals may be used, or special filler metals that mitigate hot cracking, He embrittlement or SCC may be used.

In this case, a compressive stress is generated to cause hot cracking,
It has been found that plasma transfer arc (PTA) welding can be used in water to prevent embrittlement and reduce SCC. A displacement device pressurized to a level equivalent to an 80 foot water column was used. This would allow repair welding to take place in the reactor without draining the cooling water (which would require the removal of nuclear fuel and the use of shielding to supplement the water shielding effect). It is what went. Welding requires proper establishment of the weld pool, proper bonding of the materials to be joined to the weld pool, and crack-free solidification of the weld pool. Doing this in water requires the use of local rejection devices to keep water out of the weld pool when in the liquid state. The weld pool may be formed spontaneously from the material to be joined, or it may be formed from filler metal, which can be introduced into the weld pool from powder or wire, or used for welding. It can also be introduced as a thin plate or wire that has previously been laid over the joint.

In the method of the present invention, fusion welding (f) is performed to reduce the tensile stress in the heat-affected zone of the molten and re-solidified metal and the adjacent treated material and to promote the generation of residual compressive stress.
Use usion welding or cladding techniques. In the practice of the present invention, a locally molten weld pool is formed in a protected exclusion zone by a suitable heat source, such as a welding torch, from which the surrounding environment is excluded. The rejector is attached to and moves with the torch or other heat supply. As the torch and evacuator move along the path, the weld pool begins to cool, exposing it past the protected area and exposing the weld to the surrounding environment, which acts as a quench medium. The quench fluid rapidly cools the upper surface of the weld and the heat affected zone of the treated material. Heat is removed from the fusion weld and the surrounding material by conduction through the quench medium rather than by convection as in conventional atmospheric welding. Some heat is dissipated by the flow of heat inside the bulk material being processed. But,
For the process of the present invention, most of the heat flow occurs through the quench medium. The effect of this heat flow phenomenon is the generation of compressive stress in the weld and the nearby heat affected zone.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the drawings will be described. FIG. 1 is an exploded cross-sectional view of a torch and a liquid exclusion device that provides an area where liquid is excluded. FIG. 2 is an exploded cross-sectional view of a powder splitter having a pressure relief stem.

FIG. 3 is an overall view of the powder feeding system. FIG.
FIG. 3 illustrates an exemplary use of the present invention and conditions sufficient for generating a compressive force remaining in a weld. FIG. 5 is a graph showing the relationship between the distance from the fusion tangent line of the weld in a direction parallel to the axis of the weld and the residual stress generated in the weld and the surrounding material.

FIG. 6 is a graph showing the relationship between the distance from the fusion welding line of the weld in a direction perpendicular to the surface of the weld and the residual stress generated in the weld and the surrounding material. FIG. 7 is a schematic diagram of a plasma transfer arc system for wire feed water. These drawings are comprehensive and describe devices that can be used or modified in practicing the present invention.

FIG. 1 is a cross-sectional view of a welding torch 10, for example, a plasma transfer arc torch (sometimes referred to herein as a PTA torch), a gas lens 14, and a liquid drainage device 16 useful in practicing the present invention. Is shown. Plasma transfer arc torches and gas lenses are well known in the art. Although the present invention will be described with reference to plasma transfer arc welding, the technical idea of generating residual compressive stress by underwater welding is based on other welding equipment such as laser welding, tungsten inert gas (TIG) welding and metal inert gas (MIG). ) It can be applied to welding and the like.

Referring to FIG. 1, a PTA torch 10 comprises:
It includes electrodes of voltage and current suitable for maintaining a welding arc and a gas inlet 11 for receiving a gas flow for adjusting the shape of the plasma generated by the arc. This gas is generally supplied by a so-called plasma center gas flow around a central electrode for supplying gas to the plasma.
ter gas flow) and so-called shielding gas flow (shielding
gas flow) (usually to prevent oxidation of the weld pool and HAZ, but is also used in the present invention to replace the surrounding gas or liquid at ambient hydrostatic pressure and to wrap the outer edge of the plasma). You. These gas streams are
Modified by a commercially available type of gas lens and directed in the immediate vicinity of the arc plasma. The details of the gas lens are generally not critical to the practice of the invention.
The gas lens has PTA for the convenience of replacement and replacement.
A thread (not shown) that fits with the thread 15 is provided. A powdered welding material may be introduced into the torch through the inlet 12, which forms part of the apparatus of the present invention described in detail below.

The rejection device 16 according to the invention is likewise mounted on a gas lens or torch with a thread 17 formed in a mounting collar 18. Body 19 of elimination device 16
May be conical or, more generally, cylindrical, and may be determined by providing a tip dimension A of about 1-3 inches. This dimension A defines an exclusion area larger than the length of the weld pool. Solidification of the weld should begin inside the exclusion zone. Exposure of the weld to ambient water occurs after the onset of solidification of the weld pool. Thus, dimension A forms an important aspect of the present invention with respect to generating a compressive force inside the weld.

With regard to the exclusion of the surrounding liquid, the dimension A is not a critical factor, but in practice, the skirt 20 should not be so large as to surround a harsh topology in which the skirt 20 cannot fit and maintain the liquid exclusion. It should also not be large enough to provide a perimeter of a length that increases the gas escape area so as to require more gas. Its minimum size must be able to avoid the thermal damage of the welding process as well as premature quenching of the weld (for example, liquid coming into contact with the weld pool).

The purpose of the body 19 of the exclusion device 16 is to impart a favorable geometry to the exclusion zone, otherwise the exclusion zone cannot be maintained for high hydrostatic pressures. At high hydrostatic pressure, the collapse of the bubbles near the arc allows a very rapid ingress of liquid towards the arc and the arc cannot be maintained reliably. At the same time, it is desirable to avoid turbulence or high velocity gas flow near the arc and the base metal.

The skirt 20 provides compliance with the weld bead or build-up associated with the formation of the base metal surface and the weld, and a relatively even distribution of gas escape through the body 19 of the elimination device 16 throughout the body 19. It may be made of a woven wire mesh provided by spot welding at the distal end of the rejection device to be provided by the small opening 21. The diameter of the opening is not critical, provided that the escape of gas to the hydrostatic pressure is sufficiently limited and the bubbles substantially fill the opening so that the air pressure in the evacuator is maintained. Alternatively, the body 19 can be made of a tight device wire or fibrous material, which may be woven or mated, which improves compliance with the surface of the base material and the weld. Escaping liquid through openings or interstices of wires or fibers displaces liquid, otherwise the liquid is forced into the interior by hydrostatic pressure. Elimination device 16
Gas confinement ensures that the exclusion area is maintained with low gas flow rates by maintaining a pressure above ambient hydrostatic pressure well above 80 feet due to contraction of the gas escape path from the exclusion device Also make things possible.

The exclusion zone is maintained by a combination of a plasma center gas and a shielding gas (sometimes supplemented by a powder carrier or carrier gas),
It should be understood that an independent gas supply may be provided to the rejection device itself. Therefore, the use of the exclusion device described above,
There is no limitation on the gas supply provided during operation of the welding torch. Similarly, use with a PTA torch is presently preferred, but in using the exclusion device in the present invention, not only the plasma torch described above, but also an oxygen acetylene torch, a carbon arc torch, a tungsten inert gas torch and a gas metal arc. It can be used with any heat source, including a torch. Of course, the basic invention described above does not rely on the use of a powdered welding material as suggested above (its preferred delivery system in the present invention will be described in detail below), but rather the present invention. The invention may be practiced using a conventional welding rod with a continuous supply of wire or powdered welding alloy, or by spontaneously forming a weld pool from the substrate or body to be welded. You can see that it can be done.

FIG. 2 shows a single twin feed hose powder splitter (s
The modified Y device 30 is shown as an ingle to double feed hose powdersplitter). The Y device is similar to the device normally mounted on the bottom of a gravity fed powder hopper that is placed at a height of about 3 feet or less above the torch during welding. However, as shown in the figure, the Y device has been modified in that the internal cavity 31 is widened and a hole 32 is provided on the feed side of the device and a tube 33 is mounted therein. These modifications can be facilitated by making two parts 30a and 30b with threads to fit the Y device and sealed by an O-ring seal 34, as shown. The improved Y device is preferably mounted snugly above the torch. The powder can be sent to the torch through a hose 39 attached to a barbed device fixed to the lower end of the Y device.

The use of a modified Y-device allows a controlled amount of powder-carrying gas stream to bleed through holes 32 and pipes 33, providing a significantly higher gas flow rate than can enter the torch. It can be used to transport powder. The resulting gravity feed from the splitter is such that the pressure in the splitter is balanced with the pressure inside the rejection area defined by the torch or rejection device 16 so that backflow of gas from the torch to the splitter does not occur. It is enough to send the powder to the torch. However, with regard to the control of the material flow, it is considered preferable to send a relatively small amount of gas from the splitter to the torch to facilitate the supply of powder to the torch. In any case, the volume and velocity of the gas sent to the nozzle is
The heat source can be easily reduced to a level such that the weld is formed with a single bead without significantly distorting the heat source. The principle of bleed-off of additional gas used for the convenience of powder transport is:
Applicable to any size hopper. However, a small hopper near or on the torch is preferred. This is because such small hoppers can be assembled to provide tight clearances near the weld, have a large ability to reduce gas flow to the torch consistent with good powder delivery, and withstand high internal or external pressures. This is because it has the advantage of being able to. Smaller sizes are particularly advantageous because existing equipment can be modified to provide improved powder delivery without significantly distorting the heat source.

A typical powder transfer system is shown in FIG. The powdered welding material is carried through a hose 35 to an inert gas, preferably at high pressure and speed, and conveyed to a Y device distribution block 30. The effluent carrier gas, which is expected to contain some amount of powder, is conveyed by gravity relief line 33a to gravity powder separator or recovery unit 36. Separation of the residual powder from the gas can be facilitated by providing a baffle 36a. For safety, an overpressure prevention safety valve may be provided, which will also provide a function to prevent excessive gas pressure increase in the Y device 30 (which would increase gas flow to the torch). The separated gas flows from the upper part of the powder separation / recovery device 36 through a moisture-proof filter 37 and a flow meter 38 so as to adjust the difference between the amount of the carrier gas and the allowable effluent gas amount. Of course, the difference between the carrier gas and the exhaust gas is sent to a torch to help maintain powder delivery and rejection areas.

A high quality weld is obtained because the exclusion zone can be maintained and the powder weld material can be fed to the torch operated at such hydrostatic pressure without distortion of the heat source. In addition, it has been found that underwater welding facilitated by these structures can produce residual compressive stress in the weld, resulting in reduced hot cracking, helium embrittlement, and stress corrosion cracking. The mechanism by which this cracking force is reduced is based on the presence of compressive forces that remain within the weld and adjacent areas (of the heat affected material).

The amount of heat required to establish a compressive stress is expected to be a function of the relative dimensions of the material and the rejection device. In the rejector used, the generation of compressive forces was generally most pronounced at heat inputs above 1.0 kJ / mm of weld. The details of such heat input will be a function of the rejection device diameter. FIG. 4 illustrates the creation of a weld under conditions sufficient to generate residual compressive stress and to prevent hot and stress corrosion cracking. Although underwater welding is schematically illustrated by a tank 40 containing a liquid similar to that used in the trial example of the present invention, it is not necessary to practice the present invention. The torch 10 fitted with the inert gas supply line 11, the gas lens 14, and the elimination device 16 is shown in an assembled state, and a plasma 42 reaches the surface 41 to be welded in close proximity to the surface. Placed in such a position. It will be appreciated that the exclusion device 16 is not necessary if the exclusion zone is not deep enough to produce a large hydrostatic pressure and an exclusion zone of approximately the same size as the size 43 can be established by gas flow alone. On the other hand, the tank used in the trial of the present invention could be pressurized to simulate a water depth of 80 feet or more, but under such circumstances an elimination device 16 would be required. The welding material is sent to the Y device distribution block 30 through the hose 35, and the outflowing carrier gas is discharged through the hose 33a after the pressure / flow rate adjustment and powder separation as described above. The powder welding material is conveyed to the torch 10 through the two hoses 39 as described above. Assuming a plasma transfer arc torch, electrical connection 44 supplies power to torch 10 and base material 41.

To make the weld, an inert gas is supplied through the hose 11 so that the exclusion zone develops, and an arc is ignited on the torch 10, thereby supplying heat to the surface 41 and melting the molten metal. A pond 41 is formed, and powder welding material and flux are added to the molten pool through a hose 39. The torch moves in the direction indicated by the arrow 47, and at that time, a molten pool 45 is formed so as to follow the plasma 42. The size A of the exclusion zone is chosen such that A / 2 is greater than the length of the weld pool 45, so that the weld is quenched shortly after the start of solidification, as shown in FIG.
6, a residual compressive stress is generated. These stresses are plotted in FIGS. 5 and 6 as a function of the distance from the centerline of the weld in the X and Y directions shown in FIG.

5 and 6, the stress in the sheet material welded by the present invention is compared with that of a sheet material conventionally welded in air. Tensile stress was plotted as a positive value and compressive stress was plotted as a negative value. The measurements shown in the figure are standard X
It was obtained by the line scattering method. From FIG. 5, it can be seen from FIG. 5 that in welding in the atmosphere, a considerable tensile stress is generated in a direction parallel to the welding direction and spreads over a considerable distance of the plate surface, so that it is easily damaged by stress corrosion cracking. It can be seen that the maximum value is obtained at a position near the center line of. For the same sheet material welded in air, although a slight compression force is generated at a considerable distance from the fusion line of the weld,
A considerable tensile force is generated in the weld (FIG. 5). In contrast, in welds formed in water according to the present invention, compressive stress dominates at the weld centerline,
At a distance of 5 mm to 20 mm from the welding center line, the compressive stress becomes very significant (FIG. 5). As shown in FIG. 6, a very large compressive stress occurs inside the weld and continues to a level of at least 19 mm from the fusion line, but in some samples a relatively small tensile force is observed near the fusion line. Was done.

FIG. 7 shows a method in which a filler wire is used instead of powder for forming a molten pool. It is possible to melt the area containing the crack, which facilitates self-repair.

[0030]

EXPERIMENTAL PROCEDURE A crack specimen was made using a 1 inch thick 304 stainless steel plate. In crack healing studies with PTA, cracks were simulated in one of two ways. The ends of the two steel pieces are butt-butted and shims are inserted to obtain a controlled crack of 1 inch depth and width, or a grinding wheel is cut into the steel surface to create a coin-shaped crack. In the case of a specimen made by joining two steel pieces end to end, weld only the corners of the ends and leave the front and back of the crack open, or both ends to simulate a closed crack. The shim specimen was completely welded at the corners and backside and carefully closed. Essentially all coin-shaped cracks are closed.
Some butted specimens were made to have different widths by placing shims of different widths at both corners before tacking. As a result, the maximum width at which welding can be performed with predetermined welding parameters could be quickly obtained. Another crack specimen design simulated two parallel cracks by sandwiching a 1/8 inch thick 304 stainless steel plate with two butted 1 inch thick steel plates. In this case, these cracks were always closed cracks.

All operations were performed in water in tanks designed to be pressurized to simulate various water depths. Stellite S with modified 610 type torch
A tarweld PTA system was used. This modification allows for local drainage and remote powder delivery under back-pressure conditions that occur at a simulated depth of 80 feet. The torch equipment and gas flow conditions were not changed in this limited range of studies. These parameters, as well as current, voltage and travel speed, were generally maintained at constant settings. In some cases, the heat input was increased by varying the current and speed of movement to close wide or parallel cracks or to increase the depth of penetration. Nominal equipment, gas flow and powder parameters are shown in Table 1.

The evaluation methods used to identify the results of the simulated crack healing test were visual inspection, metal microscopy of the cross section of the completed weld, and residual stress measurements on representative specimens. Visual inspection was performed to determine whether the crack was successfully sealed and to measure the weld bead width with a vernier caliper. Metallurgical microscopy determined the depth of penetration and weld quality for defects such as porosity and cracks.

[0033]

[Table 1]

Results The results of this study demonstrate the ability to hermetically weld simulated cracks wider than the crack width predicted by intergranular stress corrosion, as well as improved structural integrity. Indicate significant penetration depth for Table 2 shows that P
The conditions, parameters and measured weld bead dimensions for the TA crack healing test are shown. The first twelve items shown in Table 2 describe data on four types of open crack specimens having different crack widths. For each, the cut surface at the center point of the weld (center), at an intermediate position from the start point to the center point of the weld (start), and at an intermediate position from the center of the weld to the end point (end). I got All sections for metallurgical microscopes cross the welding direction. In these twelve items, data that applies to the entire crack specimen is shown without parentheses, and data that applies only to a specific cutting location is shown in parentheses. All other items recorded dimensional data at the cut plane cut at the center of the weld bead. Table 3 shows nominal 110 amps / 4 inches per minute /
Width successfully sealed with welding parameter of self 0.0
The result of the residual stress measurement by the X-ray diffraction method measured on the 05-inch deep 1-inch closed crack specimen is shown.

[0035]

[Table 2]

[0036]

[Table 3]

Table 2 contains two calculated values associated with each crack healing test. The value of the heat input item is the power per inch calculated based on the output current and the output voltage displayed on the power meter. The equation used to calculate this value is as follows:

[0038]

(Equation 1)

The operating supply voltage was back calculated from these values.
Also, the voltage loss associated with the 25 foot cable length used in this setup was approximately 6.5% at 110A and 16%.
It was measured to be about 9-9.5% at 5-175A. Therefore, if the transmission efficiency is neglected, the electric power sent to the base material is 6.5% to 9.5% more in accordance with the current than the value shown in Table 2.
It is considered low. Another calculated value is the aspect ratio of the weld, that is, the value obtained by dividing the penetration depth by the width of the weld bead. In this case, the maximum penetration depth was used.

[0040]

[Table 4]

From the data in Tables 2 and 3 and the results of the visual inspection of the weld, the following conclusions can be made. Results with nominal parameters at 110A current and 4 inches per minute of travel speed (300A at 60% utilization, about 1/3 of 32V rated power) without the addition of filler metal:
The open crack was sealed with a single weld pass to a maximum penetration depth of about 0.15 inches up to a limit of about 0.1 inches wide. The 0.020 inch wide 1 inch deep crack was successfully sealed in a single pass. 0.065 penetration depth
Inches. A 0.040 inch wide 1 inch deep crack was not successfully sealed in a single pass. A blowhole was created in the weld bead due to the internal water vapor pressure. A closed coin-shaped crack 0.025 inch wide and 0.23 inch deep was successfully sealed in a single pass. The penetration depth is 0.
094 inches. 0.050 inch width 0.2 depth
The closed coin-shaped crack in inches did not work due to the steam blowhole. 0.005 width each 1/8 inch apart
Two parallel tears, one inch deep, were sealed in a single pass to a depth of 0.096 inches. Width 0.01
Two 5-inch parallel cracks did not work due to steam blowholes. Increased current level (about 60% of rated voltage) with no filler added. Result: 1/8 inch wide open crack was not yet completely sealed, but penetration depth was 0. 0.3 inches.

The addition of filler material increased the current level (approximately 55% of rated voltage). Result: The 1/8 inch wide open crack was successfully sealed. The penetration depth was 0.3 inches. The result of increasing the heat input and adding the filler metal at a reduced moving speed (3 inches per minute instead of 4 inches):
Two parallel closures, each 0.005 inch wide, 1/8 inch apart, were successfully sealed to a depth of 0.118 inch in a single pass.

In the residual stress measurement performed on a representative fusion crack specimen, compressive surface residual stress was mainly recognized. However,
The stress level is about one unit greater than the typical value for underwater PTA self-welding performed on 1 inch thick solid 304 stainless steel.
0-15 ksi high (low compression), almost negligible tensile stress value (X direction only) at the weld center and light tensile stress (X direction only) 1/8 inch away from the fusion line Was. These residual stress values are nevertheless much lower than welding performed in air.

These experimental results demonstrate that the use of an underwater PTA process with local drainage can hermetically seal a simulated crack having a width greater than the crack width created by SCC. Regarding the potential of underwater PTA for structural welding, using only about 60% of the system's active power, a 1/8 inch wide gap of abutted 304 steel plates could be 0.3 inches deep and 0.65 inches wide. Demonstrated by the result of closing to width.

[Brief description of the drawings]

FIG. 1 is an exploded sectional view of a liquid removing device and a torch.

FIG. 2 is an exploded sectional view of a powder splitter.

FIG. 3 is an overall view of a powder feeding system.

FIG. 4 is a schematic view showing a specific example of underwater welding for generating a residual compressive stress.

FIG. 5 is a graph showing the relationship between the distance from the fusion tangent line of the weld in a direction parallel to the axis of the weld and the residual stress generated in the weld and the surrounding material.

FIG. 6 is a graph showing a relationship between a distance from a fusion line of the weld in a direction perpendicular to the surface of the weld and a residual stress generated in the weld and the surrounding material.

FIG. 7 is a schematic diagram of a wire feed type underwater plasma transfer arc system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Welding torch 14 Gas lens 16 Liquid elimination device 30 Y device 33a Pressure relief line 36 Powder separation device 36a Baffle 37 Moisture proof filter 38 Flow meter 39 Powder feeding hose 41 Base material

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location C21D 1/09 C21D 1/09 V 6/00 102 6/00 102Z C22F 1/10 C22F 1/10 A G21D 1/00 8719-4K 1/00 602 // C22F 1/00 602 8719-4K 630M 630 8719-4K 640A 640 8719-4K 650A 650 G21D 1/00 X (72) Inventor Raymond Allan White United States of America No. 3284 (72) Inventor Robert Anthony Fusaro, Jr., Schenecta Day, New York, USA.

Claims (12)

[Claims] 1. A method for generating a residual compressive stress in a metal selected from the group consisting of stainless steel and a nickel-based superalloy, comprising: forming a molten pool of molten metal; Form a metallurgical bond with the molten metal,
And quenching the bound metal to an ambient temperature below the melting range of the metal by contact with a quench medium. 2. The method of claim 1 further comprising: forming a molten pool of molten metal in the exclusion zone in the quench medium and moving the exclusion zone so that the metal being cooled contacts the quench medium. the method of. 3. The method of claim 2, wherein said quench medium is water. 4. The molten pool of molten metal is formed inside the rejection device by an underwater plasma transfer arc welding torch having the rejection device attached to and movable with the underwater plasma transfer arc welding torch. ,
The method of claim 3. 5. A method for generating residual compressive stress in a metal product, comprising forming a molten pool of molten metal on the product, cooling the metal to a temperature below its initial melting point, and solidifying the solidified metal. Quenching by contact with a quench medium. 6. A molten pool of the molten metal is formed by a fusion welding means, and the molten pool is cooled to a temperature lower than the initial melting point of the molten metal by ending the heating, and rapidly cooled from the solidifying metal and the adjacent heat affected zone. The method of claim 1 wherein the solidifying metal is quenched by transferring heat through the medium. 7. The molten pool of molten metal is formed by an underwater plasma transfer arc welding torch equipped with an exclusion device that removes water as the underwater plasma transfer arc welding torch moves across the metal surface. 3. The method of claim 2. 8. A method for repairing stress corrosion cracking damage in a substrate comprising stainless steel and a nickel-base superalloy material, the method comprising the steps of: Forming a weld pool, cooling the weld pool to a temperature near its melting point, and quenching the melt to ambient temperature by contact with the quenching medium when the melt is exposed from the rejection device. How to be. 9. The method of claim 8, comprising quenching the weld by contact with water. 10. The method of claim 8 wherein said weld pool is formed by heat supplied by a torch in a rejection device attached to a plasma arc transfer welding torch and said quench medium is water. 11. A method for forming a molten metal weld pool in an anhydrous rejection device with energy supplied by a plasma transfer arc welding torch attached to the rejection device, and placing the torch and the rejection device on a path to form a weld. 9. The underwater welding method according to claim 8, comprising quenching the melted part to ambient temperature by contact with water as it moves along and exposes the weld from the rejection device. 12. A drainage device defining an anhydrous area when placed on a surface to be welded, a plasma transfer arc welding torch attached to the drainage apparatus, wherein a weld pool is formed on the surface in the anhydrous area. A plasma-transferred arc welding torch adapted for forming, for forming a weld in the anhydrous zone and thereafter moving the drainage device and torch over the surface to quench the weld by contact with water. An apparatus for underwater welding, comprising: