Neutron diffraction analysis of stress and strain partitioning in a two-phase microstructure with parallel-aligned phases

Qiuliang Huang,Ondrej Muránsky,Hossein Beladi,Olena Volkova,Saurabh Kabra,Ran Shi,Javad Mola,Horst Biermann,Christian Schimpf

doi:10.1038/s41598-020-70299-1

Abstract

By time-of-flight (TOF) neutron diffraction experiments, the influence of segregation-induced microstructure bands of austenite (γ) and martensite (α′ ) phases on the partitioning of stress and strain between these phases was investigated. Initially, tensile specimens of a Co-added stainless steel were heat treated by quenching and partitioning (Q&P) processing. Tensile specimens were subsequently loaded at 350 °C parallel to the length of the bands within the apparent elastic limit of the phase mixture. Lattice parameters in both axial and transverse directions were simultaneously measured for both phases. The observation of a lattice expansion for the γ phase in the transverse direction indicated a constraint on the free transverse straining of γ arising from the banded microstructure. The lateral contraction of α′ imposed an interphase tensile microstress in the transverse direction of the γ phase. The multiaxial stress state developed in the γ phase resulted in a large deviation from the level of plastic strain expected for uniaxial loading of single phase γ. Since segregation-induced banded microstructures commonly occur in many engineering alloys, the analysis of stress and strain partitioning with the present Q&P steel can be used to interpret the observations made for further engineering alloys with two-phase microstructures.

Highlights

By time-of-flight (TOF) neutron diffraction experiments, the influence of segregation-induced microstructure bands of austenite (γ) and martensite (α′ ) phases on the partitioning of stress and strain between these phases was investigated
The influence of segregation-induced microstructure bands of α′ and γ phases aligned by caliber rolling on the partitioning of stress and strain between the phases was investigated
Tensile specimens of a quenched and partitioned Co-added stainless steel were tensile loaded parallel to the direction of the bands and the lattice parameters in the axial and transverse directions were simultaneously measured by time-of-flight neutron diffraction experiments at 350 °C

Summary

Introduction

By time-of-flight (TOF) neutron diffraction experiments, the influence of segregation-induced microstructure bands of austenite (γ) and martensite (α′ ) phases on the partitioning of stress and strain between these phases was investigated. Anisotropic length changes during the martensitic transformation of austenite in a ferritic stainless steel consisting of γ + α at high temperatures have been attributed to the planar banded arrangement of phases caused by the prior hot rolling[18]. In the latter case, ferrite acted as a constraint against the in-rolling-plane strain (strain parallel to the bands) during the transformation, causing exaggerated dimensional changes perpendicular to the bands, namely in the normal direction

Methods

Results

Conclusion