Reversion Mechanism from Deformation Induced Martensite to Austenite in Metastable Austenitic Stainless Steels

Kouki Tomimura, Setsuo Takaki, Youichi Tokunaga

Research output: Contribution to journalArticle

195 Citations (Scopus)

Abstract

Reversion mechanism from deformation induced martensite (α) to austenite (α) has been investigated in two metastable austenitic stainless steels, 15.6%Cr-9.8%Ni (the 16Cr-10Ni) and 17.6%Cr-8.8%Ni (the 18Cr-9Ni) steels, by means of magnetic analysis and transmission electron microscopy. Metastable α almost completely transforms to lath α’ by 90% cold rolling, and the α’ again reverts to γ during annealing at temperatures above 700 K. Deformation induced α’ in the 16Cr-10 Ni steel undergoes a martensitic shear reversion during heating to 923 K annealing, while that in the 18Cr-9Ni steel does a diffusional nucleation-growth reversion on 923 K annealing. Grain refining processes are greatly influenced depending on the reversion mechanism. Martensitically reversed y has a high density of dislocations immediately after the reversion and the y grains are refined through recovery and recrystallization process just like that taking place in a deformed y. On the other hand, diffusionally reversed y is characterized by the nucleation of equiaxed γ grains within the α’ matrix and the y grains gradually grow during annealing. The reversion mechanism significantly depends on the chemical compositions of steels and annealing temperature. An increase in the Ni/Cr ratio causes an increase in the Gibbs free energy change between fcc and bcc structure, leading to a fall-down of austenitizing temperature for the martensitic shear reversion. The critical driving force required for the complete martensitic shear reversion is about - 500J/mol. To obtain the critical driving force in the 18Cr-9Ni steel, it should be heated to a high temperature above 1 023 K. However, the diffusional reversion can easily occur because the martensitic shear reversion temperature is too high in the 18Cr-9Ni steel. The 16Cr-10Ni steel also undergoes the diffusional reversion when it was annealed at low temperatures below the martensitic shear reversion, 923 K.

Original languageEnglish
Pages (from-to)1431-1437
Number of pages7
Journalisij international
Volume31
Issue number12
DOIs
Publication statusPublished - Jan 1 1991

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Steel
Austenitic stainless steel
Martensite
Austenite
Annealing
Temperature
Nucleation
Cold rolling
Gibbs free energy
Refining
Transmission electron microscopy
Heating
Recovery
Chemical analysis

All Science Journal Classification (ASJC) codes

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

Cite this

Reversion Mechanism from Deformation Induced Martensite to Austenite in Metastable Austenitic Stainless Steels. / Tomimura, Kouki; Takaki, Setsuo; Tokunaga, Youichi.

In: isij international, Vol. 31, No. 12, 01.01.1991, p. 1431-1437.

Research output: Contribution to journalArticle

Tomimura, Kouki ; Takaki, Setsuo ; Tokunaga, Youichi. / Reversion Mechanism from Deformation Induced Martensite to Austenite in Metastable Austenitic Stainless Steels. In: isij international. 1991 ; Vol. 31, No. 12. pp. 1431-1437.
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abstract = "Reversion mechanism from deformation induced martensite (α) to austenite (α) has been investigated in two metastable austenitic stainless steels, 15.6{\%}Cr-9.8{\%}Ni (the 16Cr-10Ni) and 17.6{\%}Cr-8.8{\%}Ni (the 18Cr-9Ni) steels, by means of magnetic analysis and transmission electron microscopy. Metastable α almost completely transforms to lath α’ by 90{\%} cold rolling, and the α’ again reverts to γ during annealing at temperatures above 700 K. Deformation induced α’ in the 16Cr-10 Ni steel undergoes a martensitic shear reversion during heating to 923 K annealing, while that in the 18Cr-9Ni steel does a diffusional nucleation-growth reversion on 923 K annealing. Grain refining processes are greatly influenced depending on the reversion mechanism. Martensitically reversed y has a high density of dislocations immediately after the reversion and the y grains are refined through recovery and recrystallization process just like that taking place in a deformed y. On the other hand, diffusionally reversed y is characterized by the nucleation of equiaxed γ grains within the α’ matrix and the y grains gradually grow during annealing. The reversion mechanism significantly depends on the chemical compositions of steels and annealing temperature. An increase in the Ni/Cr ratio causes an increase in the Gibbs free energy change between fcc and bcc structure, leading to a fall-down of austenitizing temperature for the martensitic shear reversion. The critical driving force required for the complete martensitic shear reversion is about - 500J/mol. To obtain the critical driving force in the 18Cr-9Ni steel, it should be heated to a high temperature above 1 023 K. However, the diffusional reversion can easily occur because the martensitic shear reversion temperature is too high in the 18Cr-9Ni steel. The 16Cr-10Ni steel also undergoes the diffusional reversion when it was annealed at low temperatures below the martensitic shear reversion, 923 K.",
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