Micromechanical Effect of Martensite Attributes on Forming Limits of Dual-Phase Steels Investigated by Crystal Plasticity-Based Numerical Simulations

Tarek Hussein,Faisal Qayyum,Ulrich Prahl,Sergey Guk,Muhammad Umar

doi:10.3390/cryst12020155

Abstract

This study analyses the effect of martensite grain size and its volume fraction in dual-phase (DP) steel on (1) the formability limit, (2) average global behavior under different loading conditions, and (3) damage initiation. The virtual RVEs (Representative Volume Elements) were constructed using DREAM.3D software with a variation of microstructural attributes. The numerical simulations were carried out using DAMASK, which evaluates the polycrystalline material point behavior and solves versatile constitutive equations using a spectral solver. The simulations were post-processed to obtain global and local stress, strain, and damage evolution in constructed RVEs. The global results were processed to obtain FLDs according to Keeler-Brazier (K-B) and Marciniak and Kuczynski (M-K) criteria. In this work, the capability of microstructure-based numerical simulations to analyze the FLDs has been established successfully. From Forming Limit Diagrams (FLDs), it was observed that formability changes by changing the strain hardening coefficients (n-values), the martensite fraction, and martensite grain sizes of DP steels. The improved formability was observed with lower martensite fraction, i.e., 17%, decreased martensite grain size, i.e., 2.6 µm, and higher strain hardening coefficient. The M-K approach shows the better capability to predict the formability by various loading conditions and clarifies the necking marginal zone of FLD. The damage propagation is also strongly affected by the loading conditions. The current study would be a good guide for designers during the manufacturing and selecting of appropriate DP steels based on the service loading conditions.

Highlights

Dual-Phase (DP) steel, due to its higher energy absorption capacity and reduced weight, is used in the automotive industry to achieve simultaneous high strength and elongation goals [1,2,3]
representative volume element (RVE) were constructed by varying martensite volume fraction and martensite grain size by using DREAM.3D [27]. 4Noef x19t, the DAMASK adopts individual grains details to run numerical simulations using given load and geometry configuration files
Simulations of multi-phase DP steel were processed for 3D RVEs with damage consideration, wherein four models were virtually constructed to detect the variation in Forming Limit Diagrams (FLDs)’ behavior by varying microstructural attributes

Summary

Introduction

Dual-Phase (DP) steel, due to its higher energy absorption capacity and reduced weight, is used in the automotive industry to achieve simultaneous high strength and elongation goals [1,2,3]. Dual-phase steel is a suitable example of a multi-phase material because of the significant difference in the mechanical properties of its phases, and it has widespread usage in the automotive industry. This peculiar combination of hard and soft phases imparts desirable properties in the material, i.e., low 0.2% proof stress and a high work-hardening coefficient (n-value). The heterogeneity affects the micro-scale attributes of materials. It influences the component scale’s material properties, the material damage behavior [6]. It is of the utmost importance to investigate the relationship between the phases’ heterogeneity and their microstructural attributes, especially martensite and ferrite fractions and their grain sizes [7]

Methods

Results

Conclusion