MODIFYING Fe-30Mn-10Al-1C STEEL WITH MO AND B. IMPACT ON THE STRUCTURAL-PHASE STATE

Procesi littâ, 2024, Vol 4 (158), 66-71

Abstract

High manganese steels with high aluminum content (TWIP steels) are important materials due to their excellent combination of low density and high level of mechanical properties, which can be varied over a wide range by deformation and heat treatment. In the production of such steels, the initial structure of castings and ingots is extremely important. Refining the as-cast structure of TWIP
steels ensures a significant reduction in time and energy consumption and increases quality of finished deformed products. Modification by refractory metals addition, in particular molybdenum, is one of the most effective known ways of solving this problem. The paper presents the study of the Fe−30Mn−10Al−1C steel samples structural and phase characteristics after adding 0.25 and 0.75 wt. % molybdenum and 0.4 wt. % molybdenum with 0.003 wt. % boron The structure of the unmodified alloy is represented by a coarse-grained dendritic structure with wide discontinuous grain boundaries. Addition of 0.25 wt. % molybdenum refines structure and improves the quality of grain boundaries. When the molybdenum content increases to 0.75 wt. % signs of the ferritic
dendrites formation appear, and the structure becomes 2−3 times finer, compared to the original alloy, but ot has heterogeneous crack-like macro-graines boundaries. The addition of molybdenum around 0.4 wt. % with boron contribute to the formation of a homogeneous and uniform non-dendritic microstructure, as for the as-cast state. Increasing the molybdenum content increases the number of ferrite grains and slightly reduces the austenite stability. At the same time, Mo-bonded MnP inclusions appeared. They are formed unevenly along grain boundaries in the form of relatively large inclusions. The simultaneous addition of molybdenum and boron contributed to an increase in the proportion of ferrite and its size, as well as the formation of more compact phosphide inclusions outside the grain boundaries and with a higher efficiency of their binding, which is indicated by a twice lower content of molybdenum in their composition.