Effect of carbon and nitrogen on Md30 in metastable austenitic stainless steel

Takuro Masumura, Kohei Fujino, Toshihiro Tsuchiyama, Setsuo Takaki, Ken Kimura

Research output: Contribution to journalArticle

Abstract

Md30 is defined as the temperature at which 50 vol.% of α-martensite is formed at a true tensile strain of 0.3 in metastable austenitic steels. It has been generally believed that the effect of carbon content on Md30 was estimated to be identical to that of nitrogen as shown by Nohara's equation. However, we found in this study that Md30 in carbon-added steel is lower than that in nitrogen-added steel, which indicates that the effect of carbon content on the mechanical stability of austenite is more significant than that of nitrogen. In addition, the relationship between Md30 and carbon and nitrogen content is not linear. The effect of carbon and nitrogen content on Md30 is higher at lower carbon and nitrogen content region (<0.1%). As this effect was not considered in the previous study, the austenite-stabilizing effects of both the elements were underestimated. Therefore, in this study, new equations are proposed to accurately estimate Md30 of a Fe-Cr-Ni alloy system. As a result, modified Md30 equation is suggested as below: Md30(K) = 800 - 333√Ceq - 10.3Si - 12.5Mn - 10.5Cr - 24.0Ni - 5.6Mo Carbon equivalent, CCeq is a function of carbon and nitrogen concentrations and temperature. CCeq = C + aN a = 0.931 - 0.000281exp (0.0219T) Above equations show that the difference in austenite-stabilizing effects of carbon and nitrogen increases with rising temperature, owing to the difference in stacking fault energy between carbon-added and nitrogen-added steels.

Original languageEnglish
Pages (from-to)1163-1172
Number of pages10
JournalTetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan
Volume105
Issue number12
DOIs
Publication statusPublished - Jan 1 2019

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austenitic stainless steels
Austenitic stainless steel
Nitrogen
Carbon
nitrogen
carbon
austenite
Austenite
Steel
steels
stacking fault energy
Austenitic steel
Mechanical stability
Tensile strain
carbon steels
Stacking faults
martensite
Martensite
Temperature
Carbon steel

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Metals and Alloys
  • Materials Chemistry

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Effect of carbon and nitrogen on Md30 in metastable austenitic stainless steel. / Masumura, Takuro; Fujino, Kohei; Tsuchiyama, Toshihiro; Takaki, Setsuo; Kimura, Ken.

In: Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, Vol. 105, No. 12, 01.01.2019, p. 1163-1172.

Research output: Contribution to journalArticle

Masumura, Takuro ; Fujino, Kohei ; Tsuchiyama, Toshihiro ; Takaki, Setsuo ; Kimura, Ken. / Effect of carbon and nitrogen on Md30 in metastable austenitic stainless steel. In: Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan. 2019 ; Vol. 105, No. 12. pp. 1163-1172.
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AU - Kimura, Ken

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AB - Md30 is defined as the temperature at which 50 vol.% of α-martensite is formed at a true tensile strain of 0.3 in metastable austenitic steels. It has been generally believed that the effect of carbon content on Md30 was estimated to be identical to that of nitrogen as shown by Nohara's equation. However, we found in this study that Md30 in carbon-added steel is lower than that in nitrogen-added steel, which indicates that the effect of carbon content on the mechanical stability of austenite is more significant than that of nitrogen. In addition, the relationship between Md30 and carbon and nitrogen content is not linear. The effect of carbon and nitrogen content on Md30 is higher at lower carbon and nitrogen content region (<0.1%). As this effect was not considered in the previous study, the austenite-stabilizing effects of both the elements were underestimated. Therefore, in this study, new equations are proposed to accurately estimate Md30 of a Fe-Cr-Ni alloy system. As a result, modified Md30 equation is suggested as below: Md30(K) = 800 - 333√Ceq - 10.3Si - 12.5Mn - 10.5Cr - 24.0Ni - 5.6Mo Carbon equivalent, CCeq is a function of carbon and nitrogen concentrations and temperature. CCeq = C + aN a = 0.931 - 0.000281exp (0.0219T) Above equations show that the difference in austenite-stabilizing effects of carbon and nitrogen increases with rising temperature, owing to the difference in stacking fault energy between carbon-added and nitrogen-added steels.

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