Speaker
Description
The concept of lean medium Mn Quenching and Partitioning (Q&P) steels is supposed to be one of the promising candidates to fulfil the sophisticated requirements for third generation advanced high strength steels (AHSS). The microstructure of Q&P steels consists of a carbon-depleted martensitic matrix with a substantial volume fraction of retained austenite (RA), which undergoes the strain-induced martensitic transformation (SIMT) during deformation. Consequently, the stabilization of an optimum amount of RA by C-partitioning is essential to ensure a sufficient exploitation of the transformation induced plasticity (TRIP) effect, resulting in an excellent combination of strength and ductility. Furthermore, both volume fraction and stability of RA significantly influence the hardness-toughness relationship of Q&P steels and thus their resistance against crack propagation.
Therefore, in the present contribution several lean medium Mn steels were subjected to different Q&P heat-treatments in order to achieve microstructures containing altering volume fractions of RA. The variation of the amount of microstructural constituents, particularly that of RA, was linked to the mechanical properties such as ultimate tensile strength (UTS), total elongation (TE), hardness (HV1) and impact toughness (AK). Here, it was found that an increase of the RA content resulted in an enhanced product of UTS and TE until reaching a maximum, followed by a sharp drop as an aftermath of insufficient RA stability. On the contrary, with rising RA fractions and consequently decreasing RA stability, both HV1 and AK continuously decreased, so that their optimum combination was observed at low RA-levels. Hence, the heat-treatment parameters for achieving the optimum UTS-TE balance differed from those, which enabled the best combination of HV1 and AK, leading to the general necessity of tailoring the process parameters to the individual application fields for components made of Q&P steels.
| Speaker Country | Austria |
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