Non-Metallic Inclusions in TWIP Steel

Abstract

Twinning induced plasticity (TWIP) steels with excellent strength and elongation properties are expected to be the next generation of automotive high-strength steels. The present work investigates endogenous inclusions formed in Fe-25Mn-3Si-3Al TWIP steels in laboratorial ingot, mold casting after AOD steelmaking and electroslag remelting (ESR) process at industrial plant, respectively. The research shows that AlN and Al 2 O 3 inclusions are found as dominating inclusions, and most of them are AlN, but the number, distribution, size shape of inclusions have big differences in different metallurgical processes. The AlN inclusions in laboratorial ingot mainly present cluster states and have larger size, but after AOD or ESR process most of AlN inclusions are uniformly distributed, this would reduce harm to steel quality. From the point of view of thermodynamics, the research finds that the generation of AlN inclusions in Fe-25Mn-3Si-3Al steels is different from that of most of other high-Al steels or Al-killed steels, because many publications reported that the precipitation of AlN inclusions took place at solidifying front or solid phase, but AlN inclusions formed in Fe-25Mn-3Si-3Al steels generate in liquid steel, and related experimental results prove this point.

Investigation of Inclusion Formation in Light‐Weight Fe–Mn–Al Steels using Automated Scanning Electron Microscope Equipped with Energy‐Dispersive X‐Ray Spectroscopy

“…In addition, multiphase inclusions containing different combinations of Al 2 O 3 , AlN, and MnS were also observed. Both analysis methods, manual SEM and 3D observation, showed consistent results which were in agreement with the previous studies . Figure shows elemental mappings (Kα1 peaks) of typical multiphase inclusions observed in the steel sample using the manual SEM method.…”

“…Gigacher et al also reported the presence of Al 2 O 3 –MnO with AlN and/or MnS, single AlN, and single MnS inclusions in (15–25) Mn–3Al–3Si steels. Several other studies have reported similar types of inclusions present in AHSSs …”

“…This was done in accordance with user-defined classification rules. Due to the presence of nitride inclusions in AHSS, [5,6,8,12,14,18] it was necessary to establish appropriate inclusion classification rules for high-manganese steels. This was done by conducting a five-stage inclusion analysis.…”

“…Both analysis methods, manual SEM and 3D observation, showed consistent results which were in agreement with the previous studies. [5][6][7][8]14] Figure 3 Figure 3b. Moreover, complex multiphase inclusions containing Al 2 O 3 , AlN, and MnS were also observed (see Figure 3c).…”

“…Several other studies have reported similar types of inclusions present in AHSSs. [5,6,8] The presence of AlN-containing and a higher number of MnScontaining inclusions is peculiar to AHSSs. The formation of AlN inclusion is dictated by increased nitrogen solubility in liquid steel due to its high Mn content.…”