Individual phase constitutive properties of a TRIP-assisted QP980 steel from a combined synchrotron X-ray diffraction and crystal plasticity approach

Abstract

Microstructure-based constitutive models for multiphase steels require accurate constitutive properties of the individual phases for component forming and performance simulations. We address this requirement with a combined experimental/theoretical methodology which determines the critical resolved shear stresses and hardening parameters of the constituent phases in QP980, a TRIP assisted steel subject to a two-step quenching and partitioning heat treatment. High energy X-Ray diffraction (HEXRD) from a synchrotron source provided the average lattice strains of the ferrite, martensite, and austenite phases from the measured volume during in situ tensile deformation. The HEXRD data was then input to a computationally efficient, elastic-plastic self-consistent (EPSC) crystal plasticity model which estimated the constitutive parameters of different slip systems for the three phases via a trial-and-error approach. The EPSC-estimated parameters are then input to a finite element crystal plasticity (CPFE) model representing the QP980 tensile sample. The predicted lattice strains and global stress versus strain curves are found to be 8% lower that the EPSC model predicted values and from the HEXRD measurements, respectively. This discrepancy, which is attributed to the stiff secant assumption in the EPSC formulation, is resolved with a second step in which CPFE is used to iteratively refine the EPSC-estimated parameters. Remarkably close agreement is obtained between the theoretically-predicted and experimentally derived flow curve for the QP980 material.

The TRIP Effect and Its Application in Cold Formable Sheet Steels

“…Recently, the phase transformation kinetics of deformation‐induced martensite in the commercialized Q&P980 steel was studied by in situ synchrotron X‐ray diffraction (SYXRD) during tensile tests . Figure a shows the engineering stress–engineering strain curves of three Q&P980 specimens. The UTS is about 990 MPa and TEL is around 25% .…”

Nanoscale Solute Partitioning and Carbide Precipitation in a Multiphase TRIP Steel Analyzed by Atom Probe Tomography

“…Recently, a commercial third-generation AHHS processed with a quenching and partitioning (Q&P) heat treatment has been the subject of several studies aimed at understanding its mechanical properties and martensitic transformation. [3][4][5][6] The Q&P process increases carbon enrichment of the retained austenite for both ductility and strength enhancements. [7][8][9][10] With an as-received microstructure consisting (primarily) of ferrite (a), tempered martensite (a¢ T ), and retained austenite, this material has a 980 MPa tensile strength with 18% total elongation, making it attractive for automotive applications.…”

Carbon heterogeneities in austenite during Quenching & Partitioning (Q&P) process revealed by in situ High Energy X-Ray Diffraction (HEXRD) experiments

“…High Energy X-Ray diffraction (HEXRD) experiments conducted on synchrotron beamlines offer opportunities to go deeper in the understanding of Q&P steels. Such in situ experiments allow not only following the complex phase transformation processes and their interactions taking place during manufacturing [1][2][3][4][5][6][7][8][9] but also investigating the phase behaviors during mechanical tests on final products [10,11].…”