Austenite stabilisation by two step partitioning of manganese and carbon in a Mn-TRIP steel

Abstract

In addition to manganese, carbon partitioning has been proposed in a new medium Mn-TRIP steel by two-step partitioning during the first batching annealing and the final continuous annealing. In the second-step partitioning, the cementite dissolves and blocky austenite forms with carbon enrichment, while the partition of manganese is negligible from prior lath austenite back into ferrite due to short duration. The combined partition of carbon and manganese improves both fraction and stability of retained austenite. The alloy has exhibited the product of strength and elongation of approximately 50 GPa%. It is highlighted that there is no Lüder strain in tensile curves. The microstructure evolution and relationship of microstructure and properties have been investigated and characterised carefully in this research. This paper is part of a Thematic Issue on Medium Manganese Steels.

Enhancing the Robustness and Efficiency in the Production of Medium Mn Steels by Al Addition

“…Medium Mn steels containing 5-10 wt% Mn have been listed as one of the third-generation advanced high-strength steels for automobile application due to their attractive combination of strength and plasticity [1][2][3][4][5][6][7][8][9]. The superior mechanical properties are mainly originated from the transformation of metastable austenite into hard martensite during deformation, namely the transformation-induced plasticity (TRIP) effect [4,7,[10][11][12][13].…”

“…Medium Mn steels containing 5-10 wt% Mn have been listed as one of the third-generation advanced high-strength steels for automobile application due to their attractive combination of strength and plasticity [1][2][3][4][5][6][7][8][9]. The superior mechanical properties are mainly originated from the transformation of metastable austenite into hard martensite during deformation, namely the transformation-induced plasticity (TRIP) effect [4,7,[10][11][12][13]. In general, the volume fraction of 20% to 50% metastable austenite is retained in the final microstructure of medium Mn steels, which is greater than that of the conventional TRIP-assisted steels [2,[4][5][6]9,[14][15][16][17].…”

“…The superior mechanical properties are mainly originated from the transformation of metastable austenite into hard martensite during deformation, namely the transformation-induced plasticity (TRIP) effect [4,7,[10][11][12][13]. In general, the volume fraction of 20% to 50% metastable austenite is retained in the final microstructure of medium Mn steels, which is greater than that of the conventional TRIP-assisted steels [2,[4][5][6]9,[14][15][16][17].…”

“…A good combination of strength and plasticity can be achieved with this initial microstructure only when the annealing duration is higher than several hours to realize sufficient Mn partitioning which is only suitable for the batch annealing process in industry [26,27]. However, close control of the temperature variation is needed to produce a uniform microstructure and mechanical properties, making industrial production of this steel type difficult [4,22]. In addition, the increase in volume fraction of austenite during intercritical annealing is due to the growth of γ nucleated at the martensite lath boundaries and this process is controlled by the diffusion of Mn [5].…”

Development of New Cobalt-Free Maraging Steel with Superior Mechanical Properties via Electro-Pulsing Technology

“…Wang et al [11] reported that during aging treatment, layered reverted austenites will be formed. As the reverted austenite can reduce the {111} fiber in martensite [12] and prevent the crack propagation during tensile deformation, the ductility of maraging steels will be improved [13,14]. However, the content of reverted austenites cannot be easily controlled so that the toughening (ductility improvement) effect is unstable.…”