Knowing your manganese-Maanshan City Hyton Heavy Industry Technology Development Co.,Ltd
Manganese is an essential material in steel development for crusher wear liners. Lew Dilkes explains why an understanding of manganese will assist long service life in crushing operations. Manganese steel is the principle material used for crusher wear liners. There is 100 years of experience to draw from which suggests that not all manufacturers have fully utilised the accumulated knowledge. It is important end users understand the basics and feedback to a supplier’s deviations where expectations are not met. The purpose of this paper is to outline some of the basics for manganese steel, eg austenitic, low hardness, work hardens.
Austenitic manganese steel comprises predominantly manganese, carbon and iron in proportions that represent the many commercial grades available. The atomic arrangement of manganese steel is face centred cubic which is a densely packed lattice structure that allows for many slip planes to exist.
The atomic structure explains why austenitic materials are generally soft and ductile and with the correct chemistry will work harden to perform a number of applications. Austenitic manganese steel has outperformed any other material for crusher wear liners for over 100 years.
PROPERTIES OF MANGANESE STEEL
Manganese (Mn) dissolves substitutionally which creates barriers to the movement of dislocations. Carbon dissolves interstitially because of its small size and creates a strong resistance to the movement of dislocations. Carbon has a high solubility in austenite; austenite is non-magnetic.
Austenitic manganese steel has low thermal conductivity. The typical hardness of 14 per cent Mn steel is 200 to 220 BHN in the as-quenched heat treated condition. This does not change significantly with higher Mn contents.
Low hardness also results in good ductility and elongation and means that the yield strength of the material is low. This results in the material deforming at relatively low levels of applied stress.
In the as-quenched condition, these steels have impact strengths of up to 200 joules, as measured in the Charpy impact test, compared to a plain carbon steel (eg Grade A2) at 30 to 50 joules.
The main reason austenitic manganese steel is used in crusher parts is its ability to work harden when deformed. This results in a hard wear resistant layer forming in the deformed area but backed up by the soft and ductile core. This in effect gives it the mutually exclusive properties of hardness (wear resistance) and ductility (impact strength). Refer to the work-hardened microstructure in Figure 1.
Work hardening can only happen if the material is permanently deformed, therefore, in applications of pure or low stress abrasion, the desired property of higher hardness cannot be achieved, resulting in increased wear.