Fracture Mechanisms in Dual-Phase Steel: Influence of Martensite Volume Fraction and Ferrite Grain Size

Abstract

The influence of Martensite Volume Fraction (MVF) on fracture mechanisms in a Dual Phase steel with two different grain sizes was studied in this work. Ferrite-Martensite microstructure was obtained by an intercritical heat treatment for both groups of grain sizes. The results show a direct relationship between a higher temperature during the intercritical heat treatment and the increase of the MVF. The fine microstructure with higher MVF presents a high tensile strength and a good ductility. Furthermore, in relation to the material behavior under impact conditions, grain refinement and higher values of MVF promote ductile fracture by typical microvoid coalescence. High values of impact energy refer to the presence of low-carbon martensite formed at higher temperatures, which is more ductile than high carbon martensite formed at lower temperatures. Additionally, fine-grained materials have a better ability to dissipate impact energy. It was shown that an increase of 10.0% in MVF allows fine grain microstructures to improve their capacity to dissipate impact energy by 11.4%. This behavior may be explained because of the low carbon content of the as-received material, and the mechanical properties of the martensite obtained by the intercritical heat treatment.

Damage Evolution and Microstructural Fracture Mechanisms Related to Volume Fraction and Martensite Distribution on Dual‐Phase Steels

“…[21,22] Pakzaman et al stated that microstructure volume fraction, phase distribution, and morphology limit the deformation process and the stress partitioning. [23] Furthermore, the authors of the current study have previously documented that increasing the amount of martensite in the ferrite matrix increases the dual-phase steel mechanical response under dynamic impact conditions [24] and fatigue. [25] Due to the intercritical heat treatment temperature range used in the dual-phase steel production, the diffusion mechanism is less effective in transporting interstitial carbon atoms, so the resulting martensite produced during the quenching process has lower yield stress and hardness because of the lower and heterogeneous distribution of carbon content.…”

Processing, microstructure adjustments, and mechanical properties of dual phase steels: A review

“…Another key microstructure feature of the ferritic-pearlitic steel was the initial ferritic grain size. There have been many studies on the effects of d f on mechanical properties of ferritic-pearlitic [65-69] and resultant DP steels [70-72]. For instance, Karmakar et al [73] reported that grain refinement in DP steels led to enhancements of both strength and ductility.…”