# Study on the Grain Growth Behavior of Ultra-High Strength Stainless Steel

## TL;DR

This study examines how ultra-high-strength stainless steel grains grow at different temperatures and times, and how carbides affect this process.

## Contribution

A predictive mathematical model for austenite grain growth is developed based on the Arrhenius equation.

## Key findings

- Grain growth is slow at 900–950 °C due to the pinning effect of undissolved M6C carbides.
- Above 950 °C, carbide dissolution accelerates grain growth.
- A mathematical model explains grain growth influenced by temperature, time, and carbide count.

## Abstract

In this work, we aimed to study the austenite grain growth behavior of an ultra-high-strength stainless steel within the temperature range of 900–1150 °C and holding time range of 0–120 min, using a metallographic microscope and metallographic image analysis software to perform a statistical analysis of grain size variation. The undissolved phases of the steel were investigated using a field emission scanning electron microscope (SEM) and transmission electron microscope (TEM). Within the temperature range of 900–950 °C, the grain growth rate of the steel was slow, while within the range of 1000–1150 °C, the grain growth rate was relatively fast. This is attributed to the precipitation of a large number of M6C-type carbides during the forging and annealing processes. In the temperature range of 900–950 °C, the solid solubility of the M6C phase was low and the pinning effect was significant, which hindered the growth of austenite grains. Above 950 °C, the carbides were dissolved extensively, weakening the pinning effect on the grain boundaries and accelerating the grain growth rate. A predictive mathematical model for the growth of the original austenite grains was established based on the Arrhenius equation, elucidating the effects of heating temperature, holding time, initial grain size, and number of carbides on the growth of austenite grains, providing a theoretical basis for heat treatment process design in actual production.