What Is a Mangalloy?
Mangalloy is a special steel used in mining equipment and machine tools that contains 10-11% or more manganese in the steel.
Since the amount of manganese in ordinary steel is about 2% or less, it is a steel with a very high manganese content. It is also called Hadfield steel after its inventor. It is sometimes referred to as high man or high manganese steel.
Mangalloy is fabricated using a water toughening process. Water dust treatment is a method of heating the steel to around 1,000 to 1,100°C and then quenching it to improve toughness. This process solidifies the carbides inside the steel, thereby creating a fully austenitic structure. This operation is similar to quenching, but instead of increasing hardness, this method improves toughness, which indicates tenacity.
Uses of Mangalloys
Because mangalloy has wear resistance and toughness, is not machinable, and is mainly used for casting, it is used for relatively large items that do not require precision. In addition, since it is not magnetic, it is suitable for use in parts related to precision machinery and linear motor cars.
Examples of applications include liners for impact crushers, mill liners for grinding mills, charging shafts, cutter bars, bullrings for roller mills, railroad rail crossings, liners, and bucket teeth. It is an ideal material for use in parts subject to impact and wear, but its disadvantage is that it is difficult to machine due to severe work hardening.
Principles of Mangalloys
Figure 1. Differences between ferrite and austenite
In carbon steel, the austenite phase, which is a face-centered cubic lattice, is the stable phase at a high temperature of about 1,000°C. When carbon steel cools, the crystal structure will change to the ferrite phase. This is called transformation, and if a certain amount of a specific metal is added to carbon steel, the transformation phenomenon will not occur.
Toughness can be improved by water toughening, which dissolves the carbides that cause toughness degradation and cools them in water before they regenerate. Water toughening of general carbon steels causes a quenching effect, resulting in the formation of martensite, which makes the steel hard and brittle.
Figure 2. Water toughness treatment
Since no quenching occurs, the higher carbon content grades have more carbon in solid solution, which has the effect of increasing hardness. The carbon content of general carbon steel is about 0.3%, while mangalloy steel contains about 1% carbon.
Characteristics of Mangalloys
1. Strong Work Hardening
Figure 3. Strong work hardening of high manganese steel
The surface of mangalloy becomes harder as it is subjected to load, and its wear resistance also improves. When tensile tests are performed on mangalloys, the deformed areas are progressively work-hardened, and the undeformed areas are preferentially deformed. For this reason, it has a very good elongation performance.
This work-hardening property is responsible for the hardening and high wear resistance of manganese steel when impact is applied. Work hardening can make the material several times harder than its initial state. This steel is more advantageous in situations where large impacts are applied, such as in mining, than in situations where small impacts are applied intermittently.
2. Non-Magnetic
Although it is a steel, it is not magnetic. This is because, like austenitic stainless steel, it retains its austenitic phase.
Austenitic stainless steels can be slightly magnetic when processed, but mangalloy steels are basically non-magnetic. It should be noted that handling with magnets is not possible.
Other Information on Mangalloys
Types of Manganese Steel
In addition to mangalloys, there are manganese steels with relatively small amounts (1 to a few percent) of manganese added (low manganese steels). This material has enhanced toughness and quenching properties that are different from those of mangalloys, which use the austenite phase.
Since the mechanical properties and workability are different, it is important to select the right manganese steel for the application.