High manganese steel is an alloy steel with a manganese content greater than 10%. After solution treatment, a small amount of carbide is left undissolved in the high manganese steel. When the quantity is small and meets inspection standards, it can still be used.
In addition to carbon, manganese, silicon, sulfur and phosphorus, high manganese steel is also alloyed with nickel, titanium, chromium, vanadium, molybdenum and niobium to improve its performance.
Common types of high manganese steel include ZGMn13-1, ZGMn13-2, ZGMn13-3, ZGMn13-4 and others. By heating high manganese steel within a range of 1000 to 1100°C, a single austenite structure can be obtained.
The steel maintains its austenite structure and has high toughness after rapid water quenching (also known as water quenching treatment). Its hardness is quite low (170-230HB), which allows it to undergo plastic deformation when its surface is impacted.
As a result of strain strengthening, work hardening occurs in the deformed layer of the metal, significantly increasing the hardness of the surface layer (500-600HB). As the depth of the metal surface increases, the hardness gradually decreases.
Typically, the thickness of the hardened layer is about 10-20 mm. As high manganese steel parts continue to wear during use, the hardened layer also extends inward under the continuous impact of external loads, maintaining a stable thickness.
It should be noted that high manganese steel is not wear resistant under static conditions, it only develops wear resistance when it is continuously impacted by external loads, forming a hardened layer.
The transition temperature of high manganese steel is -40°C. In industrial production, it is mainly used to make the front wall of large excavator buckets, bucket teeth, support wheels and wear-resistant plates for crushers.
Welding rods used in arc welding of high manganese steel include high manganese steel core rods, alloy steel core rods and low carbon steel core rods. Welding rods made with high manganese steel cores are only used to repair high manganese steel components and are rarely used in production today.
Alloy steel core rods, usually made from Cr-Ni alloy steel, offer better repair quality but are more expensive. These are typically used for the first layer and as barrier layers.
Low carbon steel core rods come in two types: one is high manganese steel type such as D256 (Mn13), D266 (Mn13Mo), mainly used for high manganese steel parts subjected to strong impact and abrasive wear.
The other is Cr-Mn type rods, such as D276 and D277 (2Mn12Cr13Mo). Its deposited metal is austenite with a high manganese content, which transforms into martensite under strong impact.
Due to the high chromium content in these rods, the post-welding metal has good corrosion resistance. These rods are mainly used for corrosion-resistant coating and coating of high manganese steel, such as hydroelectric turbine blades and excavator bucket teeth.
The welding wires used for welding high manganese steel mainly include high manganese steel welding wire and alloy steel welding wire.
Welding wire with phosphorus content less than 0.03% can be used for welding and component repair; wire with a phosphorus content of more than 0.03% is used only for repairs.
High manganese steel welding wire series include Mn-Ni, Mn-Cr, Mn-Mo, Mn-Ni-Cr; Alloy steel welding wire series include Cr-Ni, Cr-Ni-Mo. These types of welding wires offer high corrosion resistance and can quickly form a hardened layer under impact.
Cr-Ni alloy steel welding wire can also be used to weld joints of different steels, such as high manganese steel and carbon steel or low alloy steel.
Whether for coating, repair or butt welding, high manganese steel has poor weldability, mainly because the heat-affected zone of welding can cause brittleness (due to carbide precipitation during welding) and thermal cracks can form in the weld seam (due to excess phosphorus and sulfur in high manganese steel and the coefficient of expansion and thermal conductivity causing crystalline cracks and settlement cracks).
During welding operations, the following must be observed: defects and surrounding hardened layers must be completely removed by grinding or carbon arc gouging. The defects of castings must undergo water hardening treatment before welding to prevent cracking.
Temperature control between layers is crucial; Before coating or repairing high manganese steel, preheating is not necessary. The lowest line power should be used and the interlayer temperature should be below 50°C to avoid excessive carbide precipitation in the heat-affected zone, leading to brittleness.
Intermittent welding or short segment welding methods can minimize heat in the base material, preventing overheating and embrittlement in the heat-affected zone. Immerse welding, where the back of the weld is immersed in water during welding, can accelerate cooling.
Compared to non-immersed welding processes, immersed welding reduces carbide precipitation and prevents the formation of hot cracks. Post-weld hammering of the weld can help alleviate welding stress and prevent cracks from forming.
When coating high manganese steel onto carbon steel or low alloy steel, a transition layer must be deposited first to prevent the appearance of martensite structures in the transition zone (or incomplete melting zone) due to a decrease in manganese content. of manganese, which could lead to cracking or peeling along the fusion line.
Therefore, a Cr-Ni austenitic stainless steel transition layer should be deposited on carbon steel or low alloy steel first. This transition layer can achieve good fusion with both carbon or low-alloy steel and high-manganese steel without forming brittle structures, thus preventing the formation of cracks.
In summary, in addition to ensuring that the selected welding current, arc voltage and welding speed can ensure proper weld formation and good fusion, the cooling speed of the workpiece must be mainly considered during the welding process.
