CHARACTERISTICS & APPLICATIONS
ímet-78M is low-hydrogen potassium, iron powder type electrode designed for use on carbon steel. In addition to their use on carbon steel, these electrodes are used for joining carbon steel to high-strength low-alloy steels and higher carbon steels. Fillet welds made in horizontal and flat welding positions have a slightly convex weld face, with a smooth and finely rippled surface. The electrodes are characterized by a smooth, quiet arc, very low spatter, and medium arc penetration. These are like ímet-781H4R electrodes, except that the testing for mechanical properties and for classification is done on a groove weld that has a 60° included angle and, for electrodes up to 4.0 mm, welded in the vertical position with upward progression. The impact test results are evaluated using all five test values and higher values are required at –30°C. The maximum allowable moisture-in-coating values in the “as-received” or reconditioned state are more restrictive than that required for ímet-78R. This classification closely corresponds to MIL-7018-M in the United States military standard MIL-E-22200/10 specification, with the exception that the absorbed moisture limits on the electrode covering and the diffusible hydrogen limits on the weld metal are not as restrictive as those in MIL-E-22200/10. ímet-78M is intended to be used with dcep type current to produce the optimum mechanical properties.
Storage and Drying Conditions: To maintain low-hydrogen electrodes with minimal moisture in their coverings, these electrodes should be stored and handled with considerable care. Electrodes which have been exposed to humidity may absorb considerable moisture and their low-hydrogen character may be lost. Then conditioning can restore their low-hydrogen character.
Hydrogen can have adverse effects on welds in some steels under certain conditions. One source of this hydrogen is moisture in the electrode coverings. For this reason, the proper storage, treatment, and handling of electrodes are necessary.
Holding Ovens: 30°C-140°C above ambient temperature. Drying Conditions: 260°C-425°C for 1-2 hours prior to use.
CHEMICAL COMPOSITION OF WELD METAL
| C | Mn | Si | P | S | Ni | Cr | Mo | V | Mn+Ni+Cr+Ni+V |
| 0.12 | 0.40-1.60 | 0.80 | 0.030 | 0.020 | 0.25 | 0.15 | 0.35 | 0.05 | NS |
Single values are maxima, except where specified otherwise.
ALL-WELD-METAL MECHANICAL PROPERTIES
| Tensile Strength, MPa | Yield Strength, At 0.2% Offset, MPa | Elongation, % | Charpy V-Notch Impact at
-30°C, Joules |
| 490 | 370-500 | 24 | 67 |
Single values are minimum or otherwise specified.
For 2.4 mm electrodes, the maximum yield strength shall be 530 MPa.
Limit of Moisture Content, % by weight max: 0.10 (As Received or Reconditioned) and 0.40 (As exposed to an environment of 27°C]/80% relative humidity (RH) for a period of not less than nine hours
Diffusible Hydrogen Content Average, Maximum, mL (H2)/100 g Deposited Metal: 4.00
ELECTRODE SIZE & WELDING CURRENT
| Diameter, mm | Length, mm | AC or DCEP, Amperes |
| 2.50 | 350 | 70-110 |
| 3.15, 3.20 | 450 | 105-155 |
| 4.00 | 450 | 130-200 |
| 5.00 | 450 | 200-275 |
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.