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Manual metal arc (MMA) welding of cast iron


Frequently Asked Questions

Manual metal arc (MMA) welding (known as SMAW in the USA) is a commonly used industrial method for joining cast iron. The good weld penetration typical of the process is actually a disadvantage, as it increases the tendency for dilution of the filler metal by the parent material. For most filler metals this is not required, and so many commercial electrodes have specially designed coatings to give the softest possible arc characteristics.

For nickel-based fillers, which are the most common choice for MMA cast iron welding, the penetration of the arc is reduced by a special graphite coating, which serves to introduce graphite into the weld pool. (Nickel based consumables designed for welding nickel alloys are therefore unsuitable for cast iron welding).

Very soft arc characteristics are also required for use of mild steel electrodes, which again is achieved by consumables designed specially for use on cast iron.

Heat input in MMA welding should be kept to a minimum, since supplying larger amounts of heat naturally leads to more extensive melting of the parent material. Use of the smallest practical electrode diameter and minimum current is therefore recommended. Some degree of control over the cooling rate, and hence the HAZ hardness can be achieved by choice of an appropriate preheat temperature. The use of post-weld heat treatment may also be beneficial.

See also Welding of cast irons - a guide to best practice , from which this FAQ is extracted.

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