The synergy between texture evolution and grain refinement in a BCC steel

ABSTRACT

This work investigates the synergy between texture evolution and grain refinement in ultra-low carbon body-centred cubic (BCC) ferritic steel. In this regard, experiments and polycrystal plasticity for ambient compressive deformation in low (up to ϵ≈0.22) and moderate (ϵ≈0.22−0.69) strain regimes were carried out. The tests were interrupted at intermediate strains for microstructure and texture characterisation. It was observed that the change in texture to $\gamma$-fibre ($\left\{111\right\}\parallel$ Compression direction$\left(\mathrm{CD}\right)$) and the formation of $\theta$-fibre $\left(\right\{100\}\parallel \mathrm{CD})$ up to $ϵ\approx 0.22$ contributes towards lattice bending, resulting in grain size reduction from $\sim 104\left(23\right)\mu \mathrm{m}$ to $\sim 23\left(6\right)\mu \mathrm{m}.$ Simultaneously, crystallite size decreases, and statistically stored dislocations (SSD) and geometrically necessary boundaries (GNB) increase rapidly. Thus, resulting in an abrupt decrease in strain hardening rate (SHR). From $ϵ\approx 0.22-0.69$, the $\gamma$ and $\theta$ -fibre broadens and $\theta$-fibre intensity increases. The low GNB density increase indicates insignificant deformation-induced lattice curvature formation within grains, resulting in SSD intensification. Thus, leading to elongated grains with sluggish grain size decrease to $\sim 17\left(4\right)\mu \mathrm{m}$ and a lesser decrease in SHR. The $\alpha$-fibre could not evolve due to the dispersion of $110$ axes along the axisymmetric radial direction due to axial deformation. The polycrystal model could appropriately simulate strain-hardening behaviour and texture evolution.

KEYWORDS:

• Ferritic steel
• microstructure
• texture
• dislocation density
• strain hardening
• polycrystal plasticity

Acknowledgement

The authors would like to acknowledge Tata Steel Ltd. Jamshedpur, India for providing the financial grant to carry out the experiments. The work also used the facility 'Light Metals and Alloys Research Lab' at the Department of Metallurgical and Materials Engineering and Central Research Facility in Indian Institute of Technology, Kharagpur, India. AKS and SB acknowledges productive discussions with Prof. R. K. Ray and Prof. J. Szpunar.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The raw/processed data required to reproduce these findings are available with the corresponding author and can be shared on demand.