Micromechanics of plastic deformation and phase transformation in a three-phase TRIP-assisted advanced high strength steel: Experiments and modeling

Abstract

a b s t r a c tThe micromechanics of plastic deformation and phase transformation in a three-phase advanced high strength steel are analyzed both experimentally and by microstructurebased simulations. The steel examined is a three-phase (ferrite, martensite and retained austenite) quenched and partitioned sheet steel with a tensile strength of $ 980 MPa. The macroscopic flow behavior and the volume fraction of martensite resulting from the austenite-martensite transformation during deformation were measured. In addition, micropillar compression specimens were extracted from the individual ferrite grains and the martensite particles, and using a flat-punch nanoindenter, stress-strain curves were obtained. Finite element simulations idealize the microstructure as a composite that contains ferrite, martensite and retained austenite. All three phases are discretely modeled using appropriate crystal plasticity based constitutive relations. Material parameters for ferrite and martensite are determined by fitting numerical predictions to the micropillar data. The constitutive relation for retained austenite takes into account contributions to the strain rate from the austenite-martensite transformation, as well as slip in both the untransformed austenite and product martensite. Parameters for the retained austenite are then determined by fitting the predicted flow stress and transformed austenite volume fraction in a 3D microstructure to experimental measurements. Simulations are used to probe the role of the retained austenite in controlling the strain hardening behavior as well as internal stress and strain distributions in the microstructure.

Non-classical crystallographic slip in a ternary carbide – Ti2AlC

“…We note that nonclassical crystallographic slip, i.e. violation of Schmid's law has been readily observed in bcc metals [20][21][22][23][24], but to the best of our knowledge, this is the first observation of non-classical crystallographic slip in a MAX phase.…”

“…Non-classical crystallographic slip, i.e. violation of Schmid's law has been readily observed in bcc metals [20][21][22][23][24], and it has been postulated that it is due to the non-planar spreading of the screw dislocation core in the presence of stresses other than the resolved shear stress [23]. In MAX phases, dislocation glide is confined to the basal plane [5][6][7], and in ref.…”

Multiphase model for transformation induced plasticity. Extended Leblond’s model

“…A mean field homogenization approach was also developed by Delannay et al (2007Delannay et al ( , 2008 based on a uniform stress/strain approximation per phase. Recent efforts were also published on the transformation in a multiphase steel by Srivastava et al (2015).…”

A differential-exponential hardening law for non-Schmid crystal plasticity finite element modeling of ferrite single crystals

“…The non-Schmid behavior has been studied in many BCC materials including molybdenum [12][13][14][15][16][17][18][19], tungsten [15][16][17][18][19][20][21][22], tantalum [1], tantalum-tungsten alloy [23] and BCC iron [11,[24][25][26][27][28]. This paper will be only concerned with the calibration and verification of the 40 CPFE for modeling of single crystal BCC metals.…”

“…These micropillars were carved out of dual-phase DP980 and three-phase QP980 steels using Focused Ion Beam 55 (FIB). The reason for using two different steels was twofold, a) deformation of ferrite in these two steels show non-Schmid behavior [25,27], and b) the ferrite phase was compressed to about 4% strain in QP980 and only showed stage I hardening, while the strain reached double that amount in DP980 and showed both stage I and stage II hardening. Given that a conventional power-law hardening model could not represent the two-stage hardening of the ferrite phase, another important goal of this paper was to develop a novel phenomenological exponential hardening rule to be implemented into the CPFE model to predict the two-stage hardening of the ferrite phase.…”