Alloy Partitioning Effect on Strength and Toughness of κ-Carbide Strengthened Steels.

Daniel M Field,Dean T Pierce,Krista R Limmer,Billy C Hornbuckle,Ken E Moore,Katherine M Sebeck

doi:10.3390/ma15051670

Abstract

Alloy partitioning during heat treatment in a lightweight precipitation hardened steel was investigated using transmission electron microscopy and atom probe tomography. The mechanical properties are discussed as a function of the effect of solution treatment temperature and aging time, giving rise to variations in chemical modulation. A wrought lightweight steel alloy with a nominal composition of Fe-30Mn-9Al-1Si-1C-0.5Mo (wt. %) was solution-treated between 1173–1273 K and aged at 773 K. Lower solution treatment temperatures retained a finer grain size and accelerated age hardening response that also produced an improved work hardening behavior with a tensile strength of −1460 MPa at 0.4 true strain. Atom probe tomography indicated these conditions also had reduced modulation in the Si and Al content due to the reduced aging time preventing silicon from diffusing out of the κ-carbide into the austenite. This work provides the framework for heat-treating lightweight, age hardenable steels with high strength and improved energy absorption.

Highlights

Weight and fuel efficiency have become a pivotal concern for vehicle designers.Lightweight steels have become one avenue for reducing weight with equivalent strength and energy absorbing capability as traditional quench and tempered steels [1,2]
Lu et al [3] investigated the microstructural response of a Fe-26Mn-9Al-0.75C alloy age hardened after cold rolling; aging was performed for a fixed time of 6hr at temperatures ranging from 773 to 1173 K
The lowest STQ temperature used in this study was 1173 K, which is 50 K greater than the maximum κ-carbide dissolution temperature recorded for this alloy through in situ synchrotron analysis by Ley et al [26]

Summary

Introduction

Lightweight steels have become one avenue for reducing weight with equivalent strength and energy absorbing capability as traditional quench and tempered steels [1,2]. Age hardening to produce κ-carbide is typically performed within the temperature range of 673–973 K [4,6]. Prior investigations have primarily focused on either investigating the isothermal aging response of a single alloy composition or exploring the effect of composition at a fixed aging condition [1,2,3,4,5,6,7,8,9]; little is known about the mechanical response and underlying mechanisms for a single alloy processed through variable thermal treatments to the same nominal strength. Pct.) alloy age hardened after cold rolling; aging was performed for a fixed time of 6hr at temperatures ranging from 773 to 1173 K.

Methods

Results

Discussion

Conclusion