The Role of Parent Phase Topology in Double Young-Kurdjumow-Sachs Variant Selection during Phase Transformation in Low-Carbon Steels

The present paper investigates the role of parent phase topology on a crystallographic variant selection rule. This rule assumes that product phase nuclei appear at certain grain boundaries in the parent structure, such that a specific crystallographic orientation relationship is observed with both parent grains at either side of the grain boundary. The specific crystallographic orientation correspondence considered here is the Young-Kurdjumow-Sachs (YKS) orientation relationship 90 degrees (which exhibits 24 symmetrical equivalents). The aforementioned relationship is characteristic of phase transformations in low-carbon steel grades. It is shown that, for different parent phase textures, similar to 20% of the grain boundaries comply with the double YKS condition allowing for a tolerance of 5 degrees, ignoring the presence of topology in the parent phase microstructure. The presented model allows for connecting the presence of a specific parent phase topology with the condition of the double YKS variant selection rule in a number of practical cases: (i) for hot rolled Ti-Interstitial Free (IF) steel with and without Mn addition, (ii) for cold rolled IF steel exhibiting very strong texture memory after forward and reverse alpha reversible arrow gamma phase transformation and (iii) for a martensitic transformation in a Fe-8.5% Cr steel. It is shown that the double YKS variant selection criterion may explain several specific features of the observed transformation textures, while assuming a non-correlated arbitrary pair topology of the parent austenite structure (implying that for N parent orientations N/2 pairs are selected in an arbitrary manner).

Automated summary

This paper investigates the influence of parent phase topology on the variant selection rule in crystalline materials. It is found that certain grain boundaries in the parent structure exhibit a specific crystallographic orientation relationship with the product phase, known as the Young-Kurdjumow-Sachs (YKS) orientation relationship. The study shows that around 20% of grain boundaries in different parent phase textures comply with the double YKS condition, regardless of the parent phase microstructure topology. The findings of this research provide insight into the formation of specific transformation textures in various practical cases.