Under low impact load, the wear resistance of medium manganese steel is better than that of high manganese steel. The manganese content of medium manganese steel is between 6% ~ 8%. Compared with high manganese steel, the MS and MD points of medium manganese steel increase. MS is lower than room temperature and MD is higher than room temperature. The single-phase austenitic bucket teeth after water toughening treatment can induce martensitic transformation and improve work hardening ability in the process of excavation and wear. There are 13mn7, 10mn7cr2 and other series of medium manganese steel developed in China. Compared with high manganese steel, they have lower toughness and greatly improved wear resistance. However, when medium manganese steel is cast or heat treated, it is easy to generate carbides in the center of the casting due to insufficient cooling, and the casting is easy to crack, which affects the service performance.
With the development of industry, the bucket capacity of excavator is becoming larger and larger. When the bucket tooth thickness of excavator is large and applied under high impact load, ultra-high manganese steel shows its advantages. Ultra high manganese steel has stable austenite structure and excellent combination of hardness and toughness, with remarkable work hardening effect. A cast ultra-high manganese steel with composition (mass fraction) of 1.1% ~ 1.6% C, 16% ~ 22% Mn, 0.30% ~ 1.00% Si, 1.50% ~ 4.0% Cr, 0.1% ~ 0.6% Ti, P content of no more than 0.1% and s content of no more than 0.05% can reach 800hv after impact wear.
In ultra-high manganese steel, the high manganese content further expands the austenite phase zone to solubilize more alloy elements and improve the solid solution strengthening ability of the matrix. Part of the gap between carbon atoms is solid dissolved in austenite. Because its radius is less than Fe and Mn, it is enriched in the compressive stress zone around the dislocation to form Coriolis gas mass. The interaction between carbon atoms and dislocation increases the motion resistance of dislocation, forms more fault sources and improves the dislocation density in the crystal. Cr and Mn can reduce the stacking fault energy, and C can reduce the stacking fault width. Their comprehensive effect makes the stacking fault energy of ultra-high manganese steel lower and the stacking fault width smaller than that of ordinary high manganese steel. This makes the bucket teeth produce a large number of stacking faults and high-density dislocations due to plastic deformation at the initial stage. When the deformation increases, twins will be formed on the basis of stacking faults. The more detailed the twins are, the more twin interfaces are, and the resistance to dislocation movement increases. This is also the reason why the hardening effect of ultra-high manganese steel is stronger than that of ordinary high manganese steel under deformation.
At present, large bucket teeth used in large impact wear conditions (such as large shovel teeth for mines) are often made of high toughness wear-resistant austenitic manganese steel to avoid impact fracture in use. Under the condition of low stress wear or small impact load, alloy high manganese steel often replaces ordinary high manganese steel. Compared with medium manganese steel, high manganese steel has higher manganese content, and work hardening is mainly realized by deformation twin and stacking fault mechanism; Medium manganese steel is mainly induced by deformation α The wear rate of high manganese steel is 3 times higher than that of high manganese steel under impact hardening mechanism. The superior combination of hardness and toughness of ultra-high manganese steel shows its advantages when the bucket tooth parts are thick and applied under high impact wear conditions.