Abstract
The objective of this work is to investigate the plastic deformation and associated microstructural evolution and damage in a martensitic steel at multiple length scales, using a combination of finite-element (FE) modelling and experimental measurements. A multiscale model is developed to predict damage evolution in the necked region of a uniaxial tensile test specimen. At the macroscale, a von Mises plasticity FE model in conjunction with a Gurson-Tvergaard-Needleman damage model is used to predict the global deformation and damage evolution. A physically-based crystal plasticity model, incorporating a damage variable is used to investigate the microscale plastic deformation behaviour and the changes in crystal orientation under large strains. The model predicts that slip bands form at the onset of plastic deformation and rotate to become almost parallel to the loading direction at large strain. In the necked region, the initially randomly orientated microstructure develops texture, brought about by inelastic deformation and lattice rotation towards the stable [011] orientation. The predicted crystal orientations and misorientation distribution are in good agreement with measurements obtained through electron backscatter diffraction in the centre of the necked region of the tensile test specimens. The experimental and modelling techniques developed in this work can be used to provide information on the evolution of plastic deformation and damage as well as the orientation-dependent crack initiation and microstructural evolution during large deformation of engineering materials.
Highlights
Tempered martensitic steels, such as P91, are widely used in current power generation plant due to their excellent high strength and corrosion resistance at elevated temperature (Abe, 2008; Chatterjee et al, 2018)
We examine orientation and block morphology changes which occur at high levels of deformation, including the formation and annihilation of high angle grain boundaries (HABs) due to large orientation changes in P91
To induce necking an initial geometric imperfection in the form of a chamfer is introduced at the bottom right corner of the rectangular region shown in Fig. 2(b), which reduces the diameter by 1%
Summary
Tempered martensitic steels, such as P91, are widely used in current power generation plant due to their excellent high strength and corrosion resistance at elevated temperature (Abe, 2008; Chatterjee et al, 2018). 9 wt% Cr is the optimum chromium concentration to obtain the highest creep rupture strength (Abe et al, 2008), due to the formation of Cr rich precipitates such as M23C6 and MX While these precipitates stabilise the fine martensitic microstructure by pinning block/lath boundaries, they may act as void initiation sites leading to damage at the microscale, as observed in (Cakan et al, 2017). Muhammad et al (2019), in particular, used a multiscale approach, incorporating a crystal plasticity finite element model at the microscale, demonstrating good agreement between predicted texture evolution under large deformation of an aluminium alloy and that obtained experimentally from EBSD scans. This paper aims to develop a multiscale model to investigate the high-temperature mechanical response, damage evolution, and microstructural evolution of a martensitic microstructure under large uniaxial deformations
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