Phase-transformation behavior and micromechanical properties of a dual-phase steel after chemical modifications

Abstract

In this work, the phase-transformation behavior and micromechanical properties of a dual-phase steel after chemical modifications were investigated theoretically and experimentally. In particular, the micromechanical behavior of the steel was modeled, based on the effects of the microstructure, phase fractions, local compositions of single phases and their area shapes. The developed model was used for predicting the damage behavior of a specimen. It was demonstrated that the tensile strength increased with the increasing temperature due to an increase in the amount of martensite in the steel, but the hardening behavior of this specimen was affected by the microstructure. Furthermore, the flow curves of the steel under different intercritical temperatures could be well predicted based on the real microstructures. The subsequent simulation results showed that while higher stress concentrated on the martensite, the shear-band appearance strongly depended on the microstructures of the phases. In addition, for the prediction of damage behaviors, the true stress/true strain curves of macroscale simulations showed good agreement with the experiments involving differently heat-treated steels. Keywords: intercritical treatment, steel, micro model V tem delu so teoreti~no in eksperimentalno preiskovali fazne spremembe in mikromehanske lastnosti dvofaznega jekla po kemijskih prilagoditvah. [e posebej je bilo modelirano mikromehansko obna{anje jekla glede na mikrostrukturo, dele`e posameznih faz, lokalno sestavo posameznih faz in njihovo morfologijo. Razviti model je bil uporabljen za napoved po{kodb vzorca. Dokazano je bilo, da se natezna trdnost pove~uje z nara{~ajo~o temperaturo zaradi nara{~anja vsebnosti martenzita v jeklu, vendar je na kaljivost tega vzorca vplivala mikrostruktura. Nadalje je bilo ugotovljeno, da je mo`no krivulje te~enja jekla pri razli~nih interkriti~nih temperaturah dobro napovedati na podlagi dejanskih mikrostruktur. Nadalje so rezultati simulacij pokazali, da so vi{je napetosti koncentrirane na martenzitu in isto~asna prisotnost stri`nih pasov, mo~no odvisne od mikrostruktur posameznih faz. Poleg tega je za napoved po{kodb pomembno, da se prave krivulje napetost-deformacija, dobljene s pomo~jo simulacij na makronivoju, dobro ujemajo z eksperimentalnimi, dobljenimi pri razli~no toplotno obdelanih jeklih.