Second-order stresses and strains in heterogeneous steels: Self-consistent modeling and X-ray diffraction analysis

Abstract

Theoretical and experimetal methods have been developed to characterize the effect of mechanical loading on the mesoscopic and macroscopic mechanical state of polycrystalline materials. Ferritic and austenitic single-phase materials were first analyzed, then phase interaction was studied in a multiductile phase material (austeno-ferritic duplex steel) and a natural reinforced composite (pearlitic steel). The theoretical method is based on the self-consistent approach in which elastic and plastic characteristics of the phases have been applied through the micromechanical behavior of single-crystal-using slip systems and microscopic hardening. The effects of a crystallographic texture and phase interaction during loading and after unloading were studied. The elastic and plastic anisotropy of the grains having the same crystallographic orientation were assessed by diffraction strain analysis. The simulation was compared with the experiments performed using the X-ray diffraction technique. In the considered duplex and pearlitic steels, it was observed that the ferrite stress state is much lower than the austenite and cementite ones. The results of diffraction strain distribution have showed the pertinence of the models and give valuable information, for example, for the yield stress and the hardening parameters of each phase in a two-phase material.

Effect of interlamellar spacing on the elastoplastic behavior of C70 pearlitic steel: Experimental results and self-consistent modeling

“…The quantitative evaluation of loading partitioning and phase behavior of pearlitic steels needs neutron [8][9][10][11] and synchrotron [4][5][6] diffraction methods which are restricted to a limited number of specialized laboratories. X-ray «in situ» tensile tests encounters difficulties associated with low intensity diffraction peak of cemetite phase.…”

“…X-ray «in situ» tensile tests encounters difficulties associated with low intensity diffraction peak of cemetite phase. They only provide information about ferrite behavior [4,5]. That is why, several studies have used self-consistent models [4,5,9,14,22] to identify the behavior of pearlitic steels at macroscopic and microscopic scales under monotonic [4,9,22] and cyclic [23] loading.…”

“…That is why, several studies have used self-consistent models [4,5,9,14,22] to identify the behavior of pearlitic steels at macroscopic and microscopic scales under monotonic [4,9,22] and cyclic [23] loading. The self-consistent model has been used by Inal et al [4] in the case of pearlitic steel (88% ferrite and 12% cementite) to identify the elastoplastic parameters (critical shear stress and hardening parameter) of ferrite. Schmitt et al [22] developed a model based on Mori-Tanaka scheme to describe the elastoplastic behavior of hypo and hyper-eutectoid steels.…”

“…Such difference in residual stress distribution between ferrite and cementite is consistent with that reported in the literature as shown in Table 10. This difference is attributed to a high contrast in the mechanical behavior between ferrite and cementite phases [4]. Moreover, the residual stress distribution is influenced by interlamellar spacing.…”

“…Nevertheless, the behavior of these materials is very sensitive to the microstructure characteristics like pearlitic colonies, early austenitic grain size and cementite volume fraction and shape. The effect of microstructure has been discussed on the basis of load partitioning between ferrite and cementite phases assessed by «in situ» tensile tests under X-ray [4,5], synchrotron [4][5][6][7] and neutron diffraction [8][9][10][11]. It has been established that for the fully pearlitic structures, the load partitioning is mainly controlled by cementite shape and the interlamellar spacing:…”