Active screen plasma nitriding of Fe-24Mn-2Al-0.45C TWIP steel: microstructure evolution and a synergistic selective oxidation mechanism

Xiao Tao; Thomas John Collins; Qingshuo Ao; Huibin Liu; Behnam Dashtbozorg; Xiaoying Li; Hanshan Dong

doi:10.1016/j.actamat.2022.118418

Active screen plasma nitriding of Fe-24Mn-2Al-0.45C TWIP steel: microstructure evolution and a synergistic selective oxidation mechanism

Xiao Tao^*, Thomas John Collins, Qingshuo Ao, Huibin Liu, Behnam Dashtbozorg, Xiaoying Li, Hanshan Dong

^*Corresponding author for this work

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Abstract

In this study, Fe-24Mn-2Al-0.45C twinning-induced plasticity (TWIP) steel was investigated after active screen plasma nitriding (ASPN) at 350–480 °C. Up to 450 °C, the ASPN-treated TWIP steel showed a double-layered structure, with a topmost Fe4N-type γ’ layer and an underlying interstitial solid solution. The underlying nitrogen interstitial solid solution obtained on ASPN-treated TWIP steel can be identified as γ_N(i), being expanded austenite with small lattice expansions at low nitrogen (and carbon) absorption levels. However, the 480 °C ASPN-treated TWIP steel surface is composed of an unexpected MnO-containing ferritic topmost layer and a thick underlying γ_N(i) layer, which corresponds to a hardness-depth profile different to those obtained at 350–480 °C. Hence, we propose and elucidate a selective oxidation mechanism (that occurred alongside nitrogen inward diffusion) on TWIP steel during ASPN treatment, which can be attributed to (a) an elevated treatment temperature that allowed Mn migration, (b) a processing atmosphere with low oxygen partial pressure, and (c) a high-Mn substrate chemical composition with low Al/Mn (or Si/Mn) ratio.

Original language	English
Article number	118418
Number of pages	17
Journal	Acta Materialia
Volume	241
Early online date	5 Oct 2022
DOIs	https://doi.org/10.1016/j.actamat.2022.118418
Publication status	Published - Dec 2022

Bibliographical note

Funding Information:
We acknowledge the Center for Electron Microscopy in the University of Birmingham for the training/support on the electron microscopes and Dr. Mingwen Bai from Coventry University for the Thermo-Calc® calculation. One of the authors, T.J.C. would also like to thank the studentship from the Center for Doctoral Training in Innovative Metal Processing (IMPaCT) funded by EPSRC, UK (EP/F006926/1).

Keywords

Active screen plasma
Expanded austenite
Plasma nitriding
Selective oxidation
Surface hardening
TWIP steel

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10.1016/j.actamat.2022.118418Licence: Creative Commons: Attribution (CC BY)

TaoX2023ActiveFinal published version, 4.99 MBLicence: Creative Commons: Attribution (CC BY)

Towards Anti-Microbial Multifunctional Stainless Steel Surfaces: Active-Screen Plasma Surface Alloying with C, N, Ag and Cu
Dong, H. (Principal Investigator), Bell, T. (Co-Investigator) & Li, X. (Co-Investigator)
Engineering & Physical Science Research Council
1/01/08 → 30/06/11
Project: Research Councils

Cite this

@article{32ffdaae2c3546699987f6101f0f7248,

title = "Active screen plasma nitriding of Fe-24Mn-2Al-0.45C TWIP steel: microstructure evolution and a synergistic selective oxidation mechanism",

abstract = "In this study, Fe-24Mn-2Al-0.45C twinning-induced plasticity (TWIP) steel was investigated after active screen plasma nitriding (ASPN) at 350–480 °C. Up to 450 °C, the ASPN-treated TWIP steel showed a double-layered structure, with a topmost Fe4N-type γ{\textquoteright} layer and an underlying interstitial solid solution. The underlying nitrogen interstitial solid solution obtained on ASPN-treated TWIP steel can be identified as γN(i), being expanded austenite with small lattice expansions at low nitrogen (and carbon) absorption levels. However, the 480 °C ASPN-treated TWIP steel surface is composed of an unexpected MnO-containing ferritic topmost layer and a thick underlying γN(i) layer, which corresponds to a hardness-depth profile different to those obtained at 350–480 °C. Hence, we propose and elucidate a selective oxidation mechanism (that occurred alongside nitrogen inward diffusion) on TWIP steel during ASPN treatment, which can be attributed to (a) an elevated treatment temperature that allowed Mn migration, (b) a processing atmosphere with low oxygen partial pressure, and (c) a high-Mn substrate chemical composition with low Al/Mn (or Si/Mn) ratio.",

keywords = "Active screen plasma, Expanded austenite, Plasma nitriding, Selective oxidation, Surface hardening, TWIP steel",

author = "Xiao Tao and Collins, {Thomas John} and Qingshuo Ao and Huibin Liu and Behnam Dashtbozorg and Xiaoying Li and Hanshan Dong",

note = "Funding Information: We acknowledge the Center for Electron Microscopy in the University of Birmingham for the training/support on the electron microscopes and Dr. Mingwen Bai from Coventry University for the Thermo-Calc{\textregistered} calculation. One of the authors, T.J.C. would also like to thank the studentship from the Center for Doctoral Training in Innovative Metal Processing (IMPaCT) funded by EPSRC, UK (EP/F006926/1). ",

year = "2022",

month = dec,

doi = "10.1016/j.actamat.2022.118418",

language = "English",

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journal = "Acta Materialia",

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T1 - Active screen plasma nitriding of Fe-24Mn-2Al-0.45C TWIP steel

T2 - microstructure evolution and a synergistic selective oxidation mechanism

AU - Tao, Xiao

AU - Collins, Thomas John

AU - Ao, Qingshuo

AU - Liu, Huibin

AU - Dashtbozorg, Behnam

AU - Li, Xiaoying

AU - Dong, Hanshan

N1 - Funding Information: We acknowledge the Center for Electron Microscopy in the University of Birmingham for the training/support on the electron microscopes and Dr. Mingwen Bai from Coventry University for the Thermo-Calc® calculation. One of the authors, T.J.C. would also like to thank the studentship from the Center for Doctoral Training in Innovative Metal Processing (IMPaCT) funded by EPSRC, UK (EP/F006926/1).

PY - 2022/12

Y1 - 2022/12

N2 - In this study, Fe-24Mn-2Al-0.45C twinning-induced plasticity (TWIP) steel was investigated after active screen plasma nitriding (ASPN) at 350–480 °C. Up to 450 °C, the ASPN-treated TWIP steel showed a double-layered structure, with a topmost Fe4N-type γ’ layer and an underlying interstitial solid solution. The underlying nitrogen interstitial solid solution obtained on ASPN-treated TWIP steel can be identified as γN(i), being expanded austenite with small lattice expansions at low nitrogen (and carbon) absorption levels. However, the 480 °C ASPN-treated TWIP steel surface is composed of an unexpected MnO-containing ferritic topmost layer and a thick underlying γN(i) layer, which corresponds to a hardness-depth profile different to those obtained at 350–480 °C. Hence, we propose and elucidate a selective oxidation mechanism (that occurred alongside nitrogen inward diffusion) on TWIP steel during ASPN treatment, which can be attributed to (a) an elevated treatment temperature that allowed Mn migration, (b) a processing atmosphere with low oxygen partial pressure, and (c) a high-Mn substrate chemical composition with low Al/Mn (or Si/Mn) ratio.

AB - In this study, Fe-24Mn-2Al-0.45C twinning-induced plasticity (TWIP) steel was investigated after active screen plasma nitriding (ASPN) at 350–480 °C. Up to 450 °C, the ASPN-treated TWIP steel showed a double-layered structure, with a topmost Fe4N-type γ’ layer and an underlying interstitial solid solution. The underlying nitrogen interstitial solid solution obtained on ASPN-treated TWIP steel can be identified as γN(i), being expanded austenite with small lattice expansions at low nitrogen (and carbon) absorption levels. However, the 480 °C ASPN-treated TWIP steel surface is composed of an unexpected MnO-containing ferritic topmost layer and a thick underlying γN(i) layer, which corresponds to a hardness-depth profile different to those obtained at 350–480 °C. Hence, we propose and elucidate a selective oxidation mechanism (that occurred alongside nitrogen inward diffusion) on TWIP steel during ASPN treatment, which can be attributed to (a) an elevated treatment temperature that allowed Mn migration, (b) a processing atmosphere with low oxygen partial pressure, and (c) a high-Mn substrate chemical composition with low Al/Mn (or Si/Mn) ratio.

KW - Active screen plasma

KW - Expanded austenite

KW - Plasma nitriding

KW - Selective oxidation

KW - Surface hardening

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U2 - 10.1016/j.actamat.2022.118418

DO - 10.1016/j.actamat.2022.118418

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VL - 241

JO - Acta Materialia

JF - Acta Materialia

M1 - 118418

ER -

Active screen plasma nitriding of Fe-24Mn-2Al-0.45C TWIP steel: microstructure evolution and a synergistic selective oxidation mechanism

Abstract

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Keywords

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Towards Anti-Microbial Multifunctional Stainless Steel Surfaces: Active-Screen Plasma Surface Alloying with C, N, Ag and Cu

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