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Abstract <p>Nickel-free austenitic steels are unique materials due to their great both corrosion resistance and mechanical properties at low temperatures, but experiences a ductile-to-brittle transition at cryogenic temperatures. The nature of embrittlement at cryogenic temperatures can be explained by studies of crystal lattice microstrains and phase transformations. To this aim the microstructure of the cast Cr–Mn–C–N austenitic steel was studied by X-ray analysis and transmission electron microscopy after both quenching from 1150°C and subsequent static tensile tests in the temperature range from 20°C down to –196°C. With lowering the test temperature, concentrations of deformation stacking faults increased, forming regions of nanometer coherent scattering. In the range from 20°C down to –90°C, the ductility reduction was accompanied by a decrease in elastic intragranular microstrains, while root-mean-square displacements of atoms from their equilibrium positions increased linearly. After testing at –90°C, the microstructure was maximally unstable. At –196°C, a reduction in the mean square displacements of atoms from their equilibrium positions was observed, along with both auxetic behavior and phase transformation into orthorhombic martensite, previously unreported for such grades.</p>

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Crystal Structure Parameters and Austenite → Orthorhombic Martensite Transition in Deformed Cast CrMnCN Steel

  • 期刊论文

  • 发表日期：

    2025年11月1日

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  • N. A. Narkevich,
  • Yu. P. Mironov,
  • I. V. Vlasov,
  • N.V. Badulin

摘要

Abstract

Nickel-free austenitic steels are unique materials due to their great both corrosion resistance and mechanical properties at low temperatures, but experiences a ductile-to-brittle transition at cryogenic temperatures. The nature of embrittlement at cryogenic temperatures can be explained by studies of crystal lattice microstrains and phase transformations. To this aim the microstructure of the cast Cr–Mn–C–N austenitic steel was studied by X-ray analysis and transmission electron microscopy after both quenching from 1150°C and subsequent static tensile tests in the temperature range from 20°C down to –196°C. With lowering the test temperature, concentrations of deformation stacking faults increased, forming regions of nanometer coherent scattering. In the range from 20°C down to –90°C, the ductility reduction was accompanied by a decrease in elastic intragranular microstrains, while root-mean-square displacements of atoms from their equilibrium positions increased linearly. After testing at –90°C, the microstructure was maximally unstable. At –196°C, a reduction in the mean square displacements of atoms from their equilibrium positions was observed, along with both auxetic behavior and phase transformation into orthorhombic martensite, previously unreported for such grades.