Crystal plasticity finite element analysis of gradient nanostructured TWIP steel. (July 2020)

• Record Type: Journal Article
• Authors: Lu, Xiaochong; Zhao, Jianfeng; Wang, Zhangwei; Gan, Bin; Zhao, Junwen; Kang, Guozheng; Zhang, Xu
• Is Part Of: International journal of plasticity. Volume 130(2020:Jul.)
• Publication Date: 2020-07
• Subjects: Gradient nanostructure -- TWIP steel -- Constitutive model -- Crystal plasticity -- Finite element method; Plasticity -- Periodicals; Plasticité -- Périodiques; Plasticity; Periodicals; 620.11233
• DOI: 10.1016/j.ijplas.2020.102703
• Languages: English
• ISSNs: 0749-6419

Abstract

Abstract: Although twinning induced plasticity (TWIP) steels have achieved a satisfactory combination of high strength and large plasticity, surface nanocrystallization realizes a further improvement of yield stress in TWIP steels without sacrificing much ductility via gradient microstructures. Experimental investigations have already revealed the excellent mechanical properties and deformation mechanisms of the gradient nanostructured (GNS) TWIP steels. But the prediction and optimization of their mechanical properties are limited due to the lack of a constitutive model. Here we establish a size-dependent crystal plasticity model containing dislocation slipping and deformation twinning, which can describe the tensile response of TWIP steels with different grain sizes. After that, this model is applied to simulate the tensile deformation behavior of the GNS TWIP steel with three kinds of gradient microstructures, namely gradient grain size, dislocation density and twin fraction. The modeling predictions are in agreement with the existing experimental data. Through the analysis of deformation contours and microstructural evolutions, the intrinsic reason for the balance of strength and ductility in the GNS TWIP steel is discussed, and the contribution of each gradient microstructure is quantized. It is found that the surface gradient region containing fine grains, high densities of dislocations and twins improves the yield stress. The homogeneous region in the core helps maintain the strain hardening ability, but the gradient region has lower strain hardening ability, which causes surface notches and slight loss of the ductility. This study offers valuable insights into predicting and further optimizing the mechanical behavior of GNS materials. Highlights: A physically based size-dependent crystal plasticity model for twinning induced plasticity (TWIP) steels is developed. A thermodynamical framework of stacking fault energy (SFE) calculation is developed for Fe-Mn-C-Ni steel system. Simulations successfully reveal the microstructure-property relation of the gradient nanostructured (GNS) TWIP steel. The individual contribution of each gradient microstructure to overall mechanical properties is quantified.