Manganese steel, sometimes called high manganese steel, and also Hadfield steel, can be identified by using a magnet. Carbon steel is magnetic; manganese steel is not. The addition of manganese to steel accomplishes three purposes:
(1) It combines with oxygen in the molten steel and thus assists in its deoxidation.
(2) It ties up any sulfur that may be present to avoid the formation of iron-sulfide inclusions that cause hot cracking.
(3) It promotes greater strength by increasing the hardenability of the steel. A bonus effect of manganese is that the fracture toughness is usually improved.
One of the most important characteristics of manganese steel is its work-hardening quality. It is relatively soft and very tough after being cast and then quenched in cold water, but as it is pounded under repeated blows in service, it becomes much harder and tougher. Under impact it will flow readily at first, but the flow sets and hardens under repeated blows. It is this quality which accounts for the difficulty in machining it with cutting tools. Machining manganese steel castings is so slow as to be impractical, and in almost all cases they are ground where necessary.
Research on Hadfield’s composition of carbon and manganese has shown that small additions of other alloying elements, such as nickel, molybdenum, and vanadium, can improve impact toughness.
Commercial alloys have a nominal composition of 1.0 to 1.4% carbon, and 10 to 14% manganese. However, in steel making practice, the carbon content is held to the mid-range and the manganese content to between 12 to 13%, since a lower range has somewhat inferior tensile properties and the upper range has no economic advantage.
Castings
Austenitic manganese steel castings are widely used as components of crushing, earthmoving, and material handling equipment. In the railroad industry they are widely used for such items as switch points, crossings, and frogs, where impact resistance and resistance to abrasive wear are primary criteria. Their nonmagnetic properties make them useful for parts for electromagnets, induction furnaces, and other electrical equipment.
Electrodes for Welding Manganese Steels. Early electrodes for welding manganese steels were based on the addition of nickel to alloys from which manganese steel welding rods and electrodes are made. These alloys contained from 3 to 5% nickel, carbon varying from 0.80 to 1.15%, silicon ranging from 0.45 to 2%, and 13 to 14% manganese. In addition to coated electrodes, tubular steel electrodes with metallic powders inside, consisting of proportions of the various elements required, have been used. However, most of the electrodes are the coated type, and in some instances a carbon steel wire core electrode is coated with the additional manganese and nickel required.
Arc Welding. Direct current electrode positive (DCEP) is recommended for welding manganese steel. Suitable welding current seems to the minimum at which the electrode will properly flow and produce satisfactory penetration, and the arc should be as short
as possible. Manufacturer’s specifications and directions should be followed for each type of electrode.
Welding Procedure. When building up the surface of a manganese steel casting, the build-up area should be divided into squares, for example, about 4 cm (1-1/2 in.) square, and the deposit confined to this square. While this deposit is hot, it should be peened vigorously to relieve strains from localized heat. Another section, at a distance from the first, may then be welded using the intermittent sequence method to keep the temperature of the casting as low as possible. It is usually recommended that the bead be rather wide, and applied with a semi-circular motion.
Safety. The maximum fume exposure guideline when welding manganese steels is 0.6 mg/m3. Local exhaust or a respirator or both should be used to prevent inhalation of fume concentration above the threshold limit value (TLV). See Hadfield Steel.