Elsevier

Acta Materialia

Volume 152, 15 June 2018, Pages 239-247
Acta Materialia

Full length article
Plastic yielding in lath martensites – An alternative viewpoint

https://doi.org/10.1016/j.actamat.2018.04.039Get rights and content

Abstract

In recent literature the gradual yielding of quenched martensitic steels has been attributed to either heterogeneous microstructures having different strength levels or to the presence of small scale, Type II, residual stresses. Using in-situ tensile testing in synchrotron diffraction experiments in combination with crystal plasticity finite element modelling (CPFEM) we show that the dominant influence on yielding derives from the residual stresses which are a product of the displacive transformation from austenite during quenching. As plastic straining proceeds, the measured diffraction peaks become narrower and asymmetric, as predicted by the CPFEM calculations. The model predictions are generally in good agreement with published results showing large variations in local strains in different microstructural elements.

Section snippets

Background

Quench-hardened medium carbon steels are undergoing a remarkable renaissance at present due to their high strength and potential for weight-saving, especially in vehicles. Although their formability is quite limited, some degree of ductility is needed in component manufacture as well as in crash situations. This concern is reflected in quite a large number of publications describing the nature of the lath martensitic microstructures [[1], [2], [3], [4], [5], [6], [7], [8], [9], [10]] and,

Conclusions

The combination of in-situ synchrotron deformation and CPFEM modelling shows that the presence of (Type II) residual stresses in martensite created during the transformation from austenite is the most important factor controlling its yielding behaviour on loading. Microstructural influences such as lath shape or carbon distributions may also play a role but are of lesser significance.

The probably unique phenomenon for martensite whereby diffraction peaks become narrower during straining is

Acknowledgements

The experiments were undertaken on the Powder Diffraction beamline at the Australian Synchrotron, Victoria, Australia. The authors thank Dr Sitarama Kada (Deakin University) for his assistance during those measurements. They also thank Professor Christopher Magee (MIT) for his comments on the manuscript. Materials were provided by SSAB Europe as part of a long-term R&D collaboration.

References (37)

  • B. Hutchinson et al.

    Microstructures and hardness of as-quenched martensites (0.1 to 0.5%C)

    Acta Mater.

    (2011)
  • P.S. Bate et al.

    Texture development in the cold rolling of IF steel

    Mater. Sci. Eng.

    (2004)
  • J.W. Morris et al.

    The nature and consequences of coherent transformations in steel

    ISIJ Int.

    (2003)
  • S. Nambu et al.

    Transition of deformation behaviour in martensitic steel during large deformation under uniaxial tensile loading

    Scripts Mater

    (2009)
  • A. Malik et al.

    Phase field modelling of martensitic transformation: effect of grain and twin boundaries

    Modelling Simul Mater

    (2013)
  • S. Allain et al.

    Toward a new interpretation of the mechanical behaviour of as-quenched low alloyed martensitic steels

    ISIJ Int.

    (2012)
  • S. Takaki et al.

    Strengthening mechanism in ultra low carbon martensitic steel

    ISIJ Int.

    (2012)
  • T. Ungar et al.

    Composite behaviour of lath martensitic steels induced by plastic strain, a new paradigm for the elasto-plastic response of martensitic steels

    Mater. Trans. A

    (2017)
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