# Through-Scale Numerical Investigation of Microstructure Evolution During the Cooling of Large-Diameter Rings

## TL;DR

This paper uses multiscale modeling to study how cooling affects the microstructure of large steel rings, helping optimize heat treatments for better material quality.

## Contribution

A novel multiscale modeling approach combining thermal simulations with phase transformation models to predict microstructure evolution in large-diameter steel rings.

## Key findings

- Thermal gradients during cooling lead to heterogeneous microstructures, especially at the ring's surface.
- Local cooling rates and initial austenite grain sizes strongly influence final grain morphology.
- The Avrami and cellular automata models provide complementary insights into phase transformation dynamics.

## Abstract

The prediction of microstructure evolution during thermal processing plays a crucial role in tailoring the mechanical properties of metallic components. Therefore, this work presents a comprehensive, multiscale modelling approach to simulating phase transformations in large-diameter steel rings during cooling. A finite-element-based thermal model was first used to simulate transient temperature distributions in a large-diameter ring under different cooling conditions, including air and water quenching. These thermal histories were subsequently employed in two complementary phase transformation models of different levels of complexity. The Avrami model provides a first-order approximation of the evolution of phase volume fractions, while a complex full-field cellular automata approach explicitly simulates the nucleation and growth of ferrite grains at the microstructural level, incorporating local kinetics and microstructural heterogeneities. The results highlight the sensitivity of final grain morphology to local cooling rates within the ring and initial austenite grain sizes. Simulations demonstrated the formation of heterogeneous microstructures, particularly pronounced in the ring’s surface region, due to sharp thermal gradients. This approach offers valuable insights for optimising heat treatment conditions to obtain high-quality large-diameter ring products.