CLASSIFICATION

ícast-NCA electrodes have been used in many of the same applications as the ENi-Fe-CI, ENiFe-CI-A, and ENiFeMn-CI electrodes. They are used to produce a low depth of fusion weld, since high dilution by the base metal may cause weld cracking.

Post weld Heat Treatment: PWHT may also be used to improve the machineability of the heat-affected zone adjacent to the weld metal. Tempering beads sometimes are employed to achieve the desired improvement. These beads, consisting entirely of filler metal and a previous bead, are made in such a manner that the heat input tempers any martensite present from a previous bead.

CHEMICAL COMPOSITION OF UNDILUTED WELD METAL

Single values shown are maximum, unless otherwise noted. *Nickel plus incidental cobalt.

Welding Considerations

The casting skin should be removed from the weld area by machining, grinding, chipping or other suitable means. When repairing casting defects, care should be exercised to ensure removal of any defective metal to sound base metal before welding. Also, all oil grease, dirt, or other foreign material should be eliminated using suitable solvents. If oil, grease, or solvents have impregnated the casting, heat should be applied to the area to be welded until volatilization is no longer observed. A temperature of 400°C generally is sufficient for this operation. If the casting is too greasy, flash heating the welding surfaces to about 540°C should drive off the grease in a gaseous state.

For V-groove welds, the edges should be beveled to form a 60-to-80-degree groove angle. For very thick base metal, a U-groove weld with a 20–25-degree groove angle and a groove radius of at least 4.8 to 13 mm should be used.

Welding currents should be within the range recommended by the supplier of the electrode, and as low as possible, consistent with smooth operation, good bead contour, and securing good fusion of the groove face. If welding is in other than flat and horizontal positions, the recommended currents should be reduced to some extent for vertical position and overhead position welding.

The electrode should be manipulated so that the width of the weld bead is no greater than three times the nominal diameter of the electrode being used. If a large cavity must be filled, the sides may be surfaced, and the cavity gradually filled toward the center of the repaired area.

When continuous welding is employed, heat input from the previous passes serves as moderate preheating or to maintain the preheat temperature. Use of preheating is not always necessary, but it is often used. In large castings, it may occasionally be found desirable to use intermittent welding to provide a more even temperature distribution, keeping the casting warm to the touch, but not permitting it to get too hot.

The hardness of the heat-affected zone is a function of the composition and cooling rate of the base metal. An increase in the cooling rate for a given composition will increase the hardness of the heat-affected zone. Thus, any steps taken to retard the cooling rate such as preheating, or the use of insulating material combined with preheating will be beneficial in lowering the hardness of the heat-affected zone. The hardness of the weld metal depends to a great extent upon the amount of dilution, and can be controlled within reasonable limits during welding. Single layer weld metal which has high dilution may have a hardness as high as 350 Brinell for ENiFe-CI, ENiFe-CI-A, and ESt electrodes, and around 210 Brinell for the ENiCI, ENiCI-A, and ENiCu-B weld metal. Moderately thick weld beads, where the dilution is reduced by directing the arc onto the weld pool, or the later layers of multiple-layer welds, may give lower hardness ranges.

Preheating is especially helpful in overcoming the differential mass effect encountered when welding a thick to a thin base metal. The use of preheat in conjunction with welding for pressure tightness also increases the resistance to cracking at the weld interface. Judicious use of preheating when welding cast iron will permit the weld and surrounding area to cool at a more uniform rate.

Peening often is used to reduce stresses and decrease distortion. Peening should be done with repeated moderate blows of a round-nose or needle tool with sufficient force to move the metal, but not enough to rupture it. Peening should be done while the metal is still above 540°C. Peening is not recommended for root beads or weld beads at the weld face.

The possibility of cracking makes it generally advisable in welding any sizable casting to employ studs that fasten the weld to the unaffected base metal below the weld interface. Studs are usually 6.4 to 16 mm in diameter, projecting 4.8 to 6.4 mm above the surface to be welded and screwed or pressed into a depth at least equal to their diameter. The cross-sectional area of the studs should be 25 to 35% of the area of the weld surface.

SIZES & CURRENT CONDITIONS (AC or DCEP)

WARNING: Safety and health information is available from many sources, including, but not limited to Safety and Health Fact Sheets listed in A11.3, ANSI Z49.1 Safety in Welding, Cutting, and Allied Processes published by the American Welding Society, 8669 Doral Blvd., Suite 130, Doral, FL 33166., and applicable federal and state regulations. The Safety and Health Fact Sheets are revised, and additional sheets added periodically.