Features of the microstructure of 20GL steel

Conclusion

Manganese has a significant influence on the structure formation and properties of 20GL steel. With a content of more than 0.6% manganese promotes the formation of a lamellar bainitic structure consisting of ferrite and microzones of residual austenite or products of its decomposition. In individual cases these microzones may be competely isolated from one another but more frequently, apparently, they form a branched skeleton of ferrite grains. Such a microstructure of heterogenized ferrite grains provides a marked effect of microcomposition strengthening of steel.

With a higher manganese content in the steel the residual austenite may remain in the form of edges on the ferritic grain boundaries. This causes significant embrittlement of the steel, especially at low temperatures. In 20GL, 20TL, and 20GFL steels with a content of up to 1.4% Mn areas with austenite edges are rarely observed and do not cause significant embrittlement of the steel.

In describing and standardization of the microstructures and evaluation of the mechanical and service properties of parts of 20GL steel it is necessary to take into consideration the nonuniformity of the structure and properties across the section of heat treated castings.