Experimental Quantification of the Austenite‐Stabilizing Effect of Mn in CrMnNi As‐Cast Stainless Steels

Abstract

In this study, the austenite-stabilizing effect of manganese in as-cast Fe-(12-16)Cr-(0-13) Mn-6Ni (concentrations in wt%) stainless steels was investigated by means of light optical microscopy (LOM) and magnetic scale measurements. The well known Schaeffler-diagram was used for the prediction of the microstructure at room temperature. Major deviations were observed between the Schaeffler-diagram predictions and the experimentally determined phase fractions. Manganese contents above 2% were found to stabilize austenite more than expected on the basis of the Schaeffler-diagram. To make that, the Schaefflerdiagram matches the experimental observations using CrMnNi steels, the boundary between austenite and austenite þ martensite regions, which denotes the beginning of the athermal martensite formation, must be displaced to lower nickel-equivalents. Alternatively, the efficiency coefficient of manganese in the Ni-equivalent formula can be increased which is preferred as it does not involve displacement of the boundaries in the Schaeffler-diagram. The best match between observed microstructures and the Schaefflerdiagram was obtained by defining the manganese efficiency coefficient in the Ni-equivalent formula as a quadratic equation of the Cr-equivalent.

Effect of Compositional Variation Induced by EBM Processing on Deformation Behavior and Phase Stability of Austenitic Cr-Mn-Ni TRIP Steel

“…The results revealed that the austenite stabilizing effect of Mn, and concomitantly the variation of martensite transformation temperatures (as quantified by the calculation of the Ni-equivalent, Ni eq ), is not constant but instead increases with increasing Cr eq . 49 This in turn also indicates that a change in Cr eq would further enhance the effect of Mn evaporation during EBM processing on the resulting mechanical response of additively manufactured specimens. This aspect should be taken into consideration for the development of future alloys tailored for AM.…”

“…By focusing on the extreme, it has been demonstrated that chemical composition and properties can be tailored by proper process adjustment, e.g., when comparing batches II and V. Future work should focus on an expansion of the methodology and a maximization of the effects of element vaporization on the mechanical and thermodynamic properties. One approach could follow findings obtained for conventionally processed material published by Wendler et al 49 It was shown that an increased Cr fraction (or Cr-equivalent, Cr eq ) has an amplifying effect on the impact of Mn. The results revealed that the austenite stabilizing effect of Mn, and concomitantly the variation of martensite transformation temperatures (as quantified by the calculation of the Ni-equivalent, Ni eq ), is not constant but instead increases with increasing Cr eq .…”

“…Furthermore, it has been shown that the alloying element Mn is prone to vaporization due to its high vapor pressure, i.e., depending on the process parameters and the volume energy, E vol , the fraction can be diminished from more than 6 wt.% Mn in the precursor powder to less than 4 wt.%. 35,46,47 Wendler et al 48,49 demonstrated for different 14Cr-XMn-6Ni-0.1N cast alloys that the Mn content not only has an effect on the stability of the respective phases but also strongly affects the SFE and, thus, the deformation mechanisms and kinetics, resulting in different stress-strain responses, tensile strengths, and total elongations.…”

Deformation Mechanisms in Austenitic TRIP/TWIP Steel as a Function of Temperature

“…[30] The chemical composition of the investigated material (Table I) is based on a patent specification for maximizing energy absorption by the TRIP effect. [31] The steel alloy was cast into sand dies with dimensions of 200 9 200 9 16 mm by ACTech GmbH, Freiberg, Germany.…”

Thermal and deformation-induced phase transformation behavior of Fe–15Cr–3Mn–3Ni–0.1N–(0.05–0.25)C austenitic and austenitic–martensitic cast stainless steels

“…This constitutional diagram was originally developed for the microstructure prediction subsequent to the welding of high-alloy steels [25]. Nevertheless, it may as well be used for the prediction of cast microstructures [26,27]. By means of the following Ni-and Cr-equivalent equations by Weiss et al [28], the austenite stability was calculated.…”