Effect of Cold Rolling on Recrystallization Behavior of Al-Free and Al-Added 15Cr-ODS Ferritic Steels

Yoosung Ha,Akihiko Kimura

doi:10.3390/cryst9030145

Abstract

The effect of cold rolling on the recrystallization behavior of Al-free and Al-added 15Cr-oxide dispersion strengthened (ODS) ferritic steels was investigated. The recrystallization of both steels are enhanced by cold rolling. The Al-free ODS steel with finer oxide particles is harder to recrystallize than Al-added ODS steel with coarser oxide particles. The effect of Al addition on the recrystallization behavior is evident. It is estimated that the recrystallization temperature of Al-free and Al-added 15Cr-ODS ferritic steel is 900 °C and 1250 °C with the annealing period of 1 h. In Al-free ODS steel, a small hardening was observed in the temperature range between 850 °C and 1200 °C, while no such phenomenon was observed in Al-added ODS steel, which is indicative of retardation of recovery by finely dispersed oxide particles. Oxide particle growth is mostly dependent on annealing temperature, while recrystallization and grain growth are controlled by not only the temperature, but the cold rolling ratio, which alters the multiple factors such as dislocation density, initial grain shape and oxide particle dispersion morphology. The cold rolling direction also influences the grain morphology and grain orientation in Al-added ODS steel, and the second rolling in a perpendicular direction to the first cold rolling direction induces the rotation of the grains from <110> to <112>. The recrystallization temperature is not significantly changed by the cold rolling direction. Recrystallization after cold rolling appears to increase the {111} grain orientation on the cold rolled specimen surface.

Highlights

Oxide dispersion strengthened (ODS) steels have been considered as candidates for fusion blanket structural materials [1] and cladding materials of generation fission reactors [2,3,4,5,6,7]
The hardness is abruptly decreased with increasing annealing temperature
The results obtained are summarized as follows;. The recrystallization of both steels are enhanced by cold rolling

Summary

Introduction

Oxide dispersion strengthened (ODS) steels have been considered as candidates for fusion blanket structural materials [1] and cladding materials of generation fission reactors [2,3,4,5,6,7] They have high strength at elevated temperatures because of the ultra-fine oxide particles dispersion which contributes to strengthening of ODS steels with high thermal stability. Annealing deformed metals at elevated temperatures results in an alteration of microstructures through the processes of recovery, recrystallization and grain growth We call this series of processes as recrystallization behavior, since the above processes often occur simultaneously and cannot be distinguished clearly.

Methods

Results

Conclusion