HASTELLOY® alloy X (HX) (UNS N06002)
Ni 47.5, Cr 21.8, Fe 18.5, Ni 9.0
HASTELLOY alloy X can be welded by metallic-arc, inert-gas-shielded arc, submerged-melt, and SIGMA methods. Hardness and tensile properties of welds made by these methods can be found on pages 6 and 11 respectively. Welding guides to assist you in using these methods are included in the sections dealing with each process.
The welding surface and adjacent area should be thoroughly cleaned down to bright metal before welding. All grease, oil, crayon marks, and other foreign matter should be removed by scrubbing with trichlorethylene or some other suitable solvent. The surface should be wiped clean before welding.
Normally, a V joint is used for butt welds in plate thickness' up ¼ in. and a U joint for greater thickness'. The V or U joint is used where the welded material will be exposed to high stresses. These joints will cause the stress to act axially. The lap or tee joint may be used for conditions of lower stress.
The U joint is preferred for material greater than ¼ in. in thickness. While the cost of preparation may be increased by this type of joint, the amount of welding materials and man-hours needed for welding will be much less than if a V joint is used. The amount of residual stress will also be lower since less weld material is required and less transverse shrinkage is incurred.
Usually, V joints should be beveled to 75- to 80-Deg. Included angle; U joints beveled to 30-Deg. Included angle with a minimum bottom radius of 3/16 in. J grooves should have a 15-Deg. Bevel with a minimum bottom radius of 3/8 in. Tee joints between dissimilar material thickness' should have a bevel of 45 Deg.
The type of joint chosen will not necessarily be affected by a change of welding process since these joint designs are standard. To make these joints suitable for automatic stressed material before welding operations, such as inert-gas-shielded arc, certain slight modifications may be necessary.
Use of a machine tool in beveling is the surest way to obtain correct fits although hand grinding can also yield satisfactory results. When sheared sheet or plate is used, the sheared edges should be ground back approximately 1/16 in. to remove any stressed material before the edge is prepared for welding. In all instances, the edges should be squared, aligned properly, and tacked before welding. Any misalignment causes variation in gap width and bead contour, which results in stresses in the weld area. These factors contribute to cracking in the weld joint. Careful preparation to assure good welds is well justified. Thermal cutting and beveling of plates can be done, but, with the exception of HELIARC cutting, these are not recommended procedures.
For good penetration, material 12-gage and heavier should be beveled and welded from both sides. When joining material of dissimilar thickness', the heavier section should always be beveled for ease of welding. Material thinner than 12-gage may be welded from one side by using proper edge spacing to allow full penetration. Care should be exercised to eliminate non-uniform penetration. This condition can leave undesirable crevices and voids in the underside of the joint which may contribute to areas of accelerated corrosion. Non-uniform penetration in material used for high-temperature applications creates stress raisers which may serve as focal points for mechanical failure.
Welding from both sides is recommended wherever possible. When this is not practical, the joint spacing should be increased and copper backing bar used. Currents slightly higher than normal are then used to obtain complete penetration.
HASTELLOY alloy X does not have the same thermal conductivity as steel, therefore, when using a standard groove, it is necessary to use a slightly larger clearance than would be needed for steel. This larger clearance insures complete penetration of the weld.
Jigs and Fixtures
Proper jigging and clamping of the weld joint holds buckling and warping to a minimum. The use of a backing bar helps to obtain a more uniform bead penetration. The bar also serves as a chill to the base metal and helps prevent excessive bead penetration. When the arc process is used, the portion of the fixture contacted by the arc should be copper. The bar should have a groove of the proper contour to permit good penetration and bead contour. For arc welding, the grooves should be of a minimum depth, usually from 1/16 to 3/32 in., and approximately 3/16 in. wide. The corners of the groove should be rounded. Square corners cause poor bead contour, flux pockets, and non-uniform beat transfer. Jigs and fixtures can be used to particular advantage when using the inert-gas-shielded arc process.
Direct current with reversed polarity produces the best mechanical properties. When joint design permits, rapid travel with as little "weaving" as possible is preferred in order to minimize heat. To avoid overheating when starting or stopping a bead, minimum currents that are consistent with the gage or size of the parts should be used. To prevent crater-cracking it may be desirable to strike the arc on a tab adjacent to the weld joint. The arc may be broken on a similar tab, however, doubling back on the bead with a slant arc is the accepted practice. Because of the fluidity of the alloy, position welding is somewhat difficult. Whenever possible, therefore, welding should be done in the flat position.
Inert-Gas-Shielded Arc Welding
In general, a minimum of heat input should be used, followed by a rapid cooling of the weld deposit. The welding currents, as listed in the following table, are dictated by the thickness of the sheet or plate to welded, not b the wire diameter. Use an electrode whose diameter is smaller than the thickness of the material to be welded. This method is not recommended for welding plate over 3/8 in. thick.
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