CLASSIFICATION

ítuf-FMC deposits nominally contain 14% manganese. This is an amount sufficient to yield austenitic weld deposits. Austenite is a nonmagnetic, tough form of steel. To preserve the toughness, excessive heat must be avoided during welding. Stringer beads and a block sequence are recommended. The additions of other elements, such as 4% nickel, are made to give more stability to the austenite; chromium is also added to the extent of 4% to increase the yield strength. Abrasion resistance is only a little better than that of low-carbon steel unless there has been sufficient impact to cause work hardening. As-deposited surfaces generally are no harder than HRC 20 but can work harden to HRC 55. Since deposits are difficult to machine, grinding is preferred for finishing.

Applications

These electrodes are used for the rebuilding, repair, and joining of Hadfield austenitic manganese steel. The ability to absorb high impact makes such deposits ideal for the rebuilding of worn rock crushing equipment and parts subject to impact loading, such as railroad frogs.

Welding Considerations

Role of Hydrogen in Surfacing: Hydrogen can be detrimental to surfacing deposits. The effect varies widely from one alloy type to another. In general, hydrogen’s detrimental effect on microstructure is the most pronounced for martensitic types, with austenitic types being the least affected. Other factors influencing hydrogen’s effect include carbon and alloy contents plus in-service welding variables. In welding there are many sources for hydrogen contamination. Coating moisture is one of the most important. Most electrodes are manufactured and packaged to control moisture. When received, consideration must be given to proper storage to prevent moisture pick-up. During use, improper regard to welding procedure and environmental variables can result in spalling or “hydrogen-induced” (under bead) cracking.

Low equipment cost, great versatility, and general convenience make manual shielded metal arc welding very popular. The welding machine, which is essentially a power conversion device, is usually the main item of equipment needed. It may be a motor- generator, transformer, transformer-rectifier combination, or fuel-operated engine combined with a generator. The arc power may be either direct or alternating current. The filler metal is in the form of covered electrodes. (Bare electrode arc welding is a rarity today, though it is feasible with austenitic manganese steel electrodes). Welding can be done in almost any location and is practicable for a variety of work, ranging from very small to quite large. For some applications, it is the only feasible method; and, for many others (especially where continuous methods do not offer significant benefits), it is the economical choice. The operation is under the observation and control of the welder, who can easily cover irregular areas and often correct for adverse conditions. It is also helpful if the welder exercises judgment in other matters, such as holding the arc power down to minimize cracking; keeping a short arc and avoiding excessive puddling to minimize the loss of expensive alloying elements in the filler metal; minimizing dilution with base metal; and restricting hydrogen pickup. This process is used extensively for hard facing, buttering, buildup, and cladding. Surfacing of carbon and low-alloy steels, high-alloy steels, and many nonferrous metals may be done with the shielded metal arc process. Base metal thicknesses may range from below 6–450 mm or more. The surfacing metals employed include low- and high-alloy steels, stainless steels, nickel-base alloys, cobalt-base alloys, and copper-base alloys. The welding conditions for surfacing are not fundamentally different from those used in welding a joint. The arc and weld pool are shielded by the slag or the gases, or both, produced by the electrode. The type of covering on the electrode has considerable effect on the characteristics of the weld metal. Surfacing can be done on work ranging in size from very small to quite large.

Various shielded metal arc process variables affect the three most important surfacing characteristics: dilution, deposition rate, and deposit thickness.

These factors may make it unwise to change only the indicated variable; this in turn may mean that the desired change in dilution, deposition rate, or deposit thickness may not be achieved. For example, a given welding procedure with a small electrode diameter may produce high dilution.

This indicates that a change to a large size electrode will decrease dilution. This is true, however, only if the amperage, travel speed, position, etc., also remain constant. In many cases, a larger amperage value must be used with the larger electrode size to obtain acceptable weld quality. In this case, the dilution may remain constant or even increase with the change to the larger electrode size. The process usually achieves a deposition rate from 0.5–2 kg per hour at dilution levels from 30–50%.

Holding Ovens: 30°C-140°C above ambient temperature.

Drying Conditions: 260°C-425°C for 1-2 hour prior to use.

CHEMICAL COMPOSITION OF UNDILUTED WELD METAL, %

Single values are maximum. Rem = Remainder

Sulfur and phosphorus contents each shall not exceed 0.035%.

EFFECT OF SMA VARIABLES ON THE THREE MOST IMPORTANT CHARACTERISTICS OF SURFACING

SIZES & CURRENT CONDITIONS (AC or DCEP or DCEN)

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.