Tailoring the Austenite Fraction of a Cu and Ni Containing Medium-Mn Steel via Warm Rolling

Zigan Xu,Xiao Shen,Jiyao Li,Wenwen Song,Silvia Richter,Wolfgang Bleck,Tarek Allam

doi:10.3390/met11121888

Abstract

Developing medium-Mn steels (MMnS) demands a better understanding of the microstructure evolution during thermo-mechanical treatments (TMTs). This study demonstrates the relationship among processing, microstructure, and mechanical properties of a warm-rolled medium-Mn steel (MMnS) containing 1.5 wt. % Cu and 1.5 wt. % Ni. After short-time warm rolling (WR) in an intercritical temperature range, a significant quantity (40.6 vol.%) of austenite was reverted and retained after air cooling. The microstructure and tensile properties of the WR specimens were compared with two typical process routes, namely hot rolling+ cold rolling+ annealing+ tempering (CRAT) and warm rolling+ annealing+ tempering (WRAT). The WR specimen exhibited comparable tensile properties with the CRAT specimens (967 MPa yield strength, 1155 MPa tensile strength, 23% total elongation), with a remarkably shortened process route, which was derived from the dislocation accumulation and austenite reversion during rolling. The WR route stands out among the traditional CRAT and the extended WRAT routes for its excellent tensile properties and compact processing route.

Highlights

Medium-Mn steels (MMnS) with 3–12 wt. % Mn content have been identified as prime candidates for third generation advanced high-strength steels, because of their superior combination of strength and ductility [1]
For the cold rolling+ annealing+ tempering (CRAT) and warm rolling+ annealing+ tempering (WRAT) processes, the yield strengths of the 1.5Cu1.5Ni specimens were improved compared to the 0Cu0Ni specimens, which could be attributed to the precipitation of Cu-rich particles during tempering
It should be noted that the 1.5Cu1.5Ni-warm rolling (WR) specimen did not go through any post-rolling annealing or tempering, it already exhibited excellent tensile properties (YS 967 MPa, TS 1155 MPa, TE 23%), which were slightly better than the 0Cu0NiWR specimen

Summary

Introduction

Medium-Mn steels (MMnS) with 3–12 wt. % Mn content have been identified as prime candidates for third generation advanced high-strength steels, because of their superior combination of strength and ductility [1]. % Mn content have been identified as prime candidates for third generation advanced high-strength steels, because of their superior combination of strength and ductility [1]. These steels exhibit a fully α’-martensite microstructure in the hot-rolled and cold-rolled states [2,3]. Their excellent mechanical properties emerge when austenite-reverted transformation (ART) annealing [4] in the intercritical temperature range is applied to tailor their ultrafine-grained (UFG) duplex microstructure, which consists of tempered martensite and retained austenite (RA). For the conventional production of MMnS through hot rolling and cold rolling [7,8], single or multiple post-processing steps were required to adjust the microstructure of MMnS and derive improved mechanical properties

Methods

Results

Conclusion