The role of aluminium in chemical and phase segregation in a TRIP-assisted dual phase steel

Abstract

In this work we demonstrate that micro-segregation patterns of alloying elements present in a high-strength TRIP-assisted DP steel after casting are retained in the microstructure throughout processing, and lead to anisotropy (banding) in the final microstructure. In particular, we have assessed the role of Al on the chemical segregation of Mn, Cr and Si during casting, and their impact on the phase transformations occurring during thermo-mechanical processing of the as-cast material. We have derived the elemental partition coefficients, based on the experimentally determined dendrite spacing and chemical profiles in the as-cast structure, and used them to derive the local austenite-to-ferrite transformation temperature. Our cellular automaton methodology to simulate phase transformations allows reliable prediction of the formation or suppression of banding in the intermediate and final microstructures for different heating or cooling rates. Our results reveal that aluminium exerts the largest individual effect of the substitutional elements on the formation of banding in these steels. Controlling micro-segregation during solidification in advanced high-strength multiphase steels is therefore critical for obtaining homogeneous mechanical properties in the final product, as it controls the phase transformations occurring during thermo-mechanical processing and therefore the final microstructure

Hot-Dip Aluminizing on AISI F55–UNS S32760 Super Duplex Stainless Steel Properties: Effect of Thermal Treatments

“…Further, aluminum acts as strong ferrite-stabilizer element, promoting the austenite to ferrite phase transformation and drastically increasing the local ferrite volume fraction [46]. Thus, the collected data prove the complete irrelevance of austenite content and morphology on the hot-dip aluminizing.…”

Work hardening behaviour in banded dual phase steel structures with improved formability

“…In our previous work we demonstrated that micro-segregation patterns of alloying elements present after casting in a high-strength DH steel are retained in the microstructure throughout thermo-mechanical processing, leading to martensite-rich banding in the final microstructure [5]. Aluminium was shown to have a hitherto overlooked role in the segregation of alloying elements during casting, and the single largest influence on the phase transformations occurring during processing that lead to banding in this steel.…”

“…The steel under investigation is a high-strength dual phase steel with improved formability, termed DH800, produced via continuous casting followed by hot-rolling (HR), cold-rolling (CR) and continuous annealing. The chemical composition of this steel is given in Table 1, together with the segregation coefficient of the relevant elements [5]. [12,13].…”

“…The blocks were subsequently hot-and cold-rolled, followed by a continuous annealing designed specifically to either promote or suppress the occurrence of banding in the microstructure, generating B (banded) and NB (non-banded) structures respectively [5]. The annealing process was simulated using a 3D cellular automaton model [12].…”

Dataset concerning the analytical approximation of the Ae3 temperature

“…(6) in Ref. [1]:$A{e}_3(°C)=c_0+\sum _{X,k}{c}_{Xk}{X}^k+\sum _{X,Y,k,m}{c}_{XkYm}{X}^k{Y}^m+\sum _{X,Y,Z,k,m,n}{c}_{XkYmZn}{X}^k{Y}^m{Z}^n$where Ae 3 temperature is expressed in °C and concentrations in wt. %.…”