# Precipitation of β-Mn in the Form of Widmanstätten Side-Plates in the Ferrite Matrix of an Fe–28.6 Mn–10.9 Al Alloy Steel

## TL;DR

This study examines how β-Mn precipitates form in a high-Mn steel alloy, providing insights into its stability and structure for lightweight steel development.

## Contribution

The paper clarifies the precipitation behavior and crystallography of β-Mn in Fe–Mn–Al alloys, offering new insights for lightweight steel design.

## Key findings

- β-Mn precipitates form as Widmanstätten side-plates in the BCC ferrite matrix.
- β-Mn is thermally stable between 500 °C and 850 °C, with maximum volume fraction near 650 °C.
- A specific orientation relationship is established between β-Mn and ferrite phases.

## Abstract

The Fe–28.6 Mn–10.9 Al alloy is BCC ferrite at temperatures between 850 and 1100 °C.β-Mn exists in the ferrite at temperatures ranging from 500 °C to 850 °C.β-Mn phase is formed as Widmanstätten side-plates.The formation of the β-Mn in BCC shows the following OR: (021¯)β
// (100)α and [1¯12]β
// [012]α.

The Fe–28.6 Mn–10.9 Al alloy is BCC ferrite at temperatures between 850 and 1100 °C.

β-Mn exists in the ferrite at temperatures ranging from 500 °C to 850 °C.

β-Mn phase is formed as Widmanstätten side-plates.

The formation of the β-Mn in BCC shows the following OR: (021¯)β
// (100)α and [1¯12]β
// [012]α.

What are the main findings?
The alloy exhibits a single BCC phase at temperatures above 850 °C.β-Mn is thermally stable between 500 °C and 850 °C.β-Mn appears as Widmanstätten side-plates that coarsen with temperature.The β-Mn in BCC shows an OR established as (021¯)β // (100)α and [1¯12]β // [012]α.

The alloy exhibits a single BCC phase at temperatures above 850 °C.

β-Mn is thermally stable between 500 °C and 850 °C.

β-Mn appears as Widmanstätten side-plates that coarsen with temperature.

The β-Mn in BCC shows an OR established as (021¯)β // (100)α and [1¯12]β // [012]α.

What are the implications of the main findings?
We clarify the precipitation behavior of β-Mn.We provide new insights into β-Mn phase stability in Fe–Mn–Al alloy.We provide information contributing to the development of high-strength, lightweight steels.

We clarify the precipitation behavior of β-Mn.

We provide new insights into β-Mn phase stability in Fe–Mn–Al alloy.

We provide information contributing to the development of high-strength, lightweight steels.

The microstructural evolution and phase stability in Fe–Mn–Al alloys play a decisive role in determining their mechanical performance and potential applications. This study investigates the precipitation behavior and crystallography of the β-Mn phase in an Fe–28.6 Mn–10.9 Al (wt.%) alloy subjected to annealing at 1100 °C, followed by water quenching and subsequent isothermal holding at temperatures between 500 °C and 900 °C for 20 h. Microstructural analysis using X-ray diffraction, optical and electron microscopy revealed a single body-centered cubic (BCC) ferritic matrix above 850 °C and the formation of β-Mn precipitates with Widmanstätten side-plate morphology at lower temperatures. The β-Mn phase was thermally stable between ~500 °C and 850 °C, with the volume fraction increasing with temperature and reaching a maximum near 650 °C. The β-Mn precipitates coarsened progressively with increasing temperature and were found to be richer in Mn than the surrounding Fe-rich BCC matrix. Crystallographic analysis established an orientation relationship (OR) of (021¯)β // (100)α and [1¯12]β // [012]α, where // denotes nearly parallel alignment, signifying a semi-coherent interface between the two structures. These findings clarify β-Mn precipitation, its interfacial relationship with ferrite, and its thermal stability in high-Mn Fe–Mn–Al alloys, offering guidance for microstructural design in next-generation lightweight steels.