Characterization of a Medium Mn-Ni Steel Q&amp;P Treated by a High Partitioning Temperature Cycle

Maribel Arribas,Daniele De Caro,Maria J Santofimia,Teresa Gutiérrez,David Martin,Eider Del Molino,Artem Arlazarov,Sudhindra Ayenampudi

doi:10.3390/met12030483

Abstract

In this work, a medium Mn-Ni steel was treated through Quenching and Partitioning (Q&P) with a partitioning temperature (PT) of 650 °C, which corresponded to the start of the austenite reverse transformation (ART) phenomenon. The influence of the quenching temperature (QT) and partitioning time (Pt) on austenite stabilization and mechanical properties was investigated. A strong influence of the quenching temperature was observed. Results were compared with those obtained after a Q&P treatment with 400 °C partitioning temperature. The Q&P cycle with quenching to room temperature and a high partitioning temperature produced a steel with a high retained austenite (RA) volume fraction and exceptional strength–ductility balance. The analysis of the mechanical stability of the retained austenite revealed a significant stress-induced transformation. Nevertheless, the austenite, which was stable at stresses above the yield stress, provided significant TRIP-assisted ductility. Bending, hole expansion and post-stamping properties were also evaluated for the most promising conditions.

Highlights

ArcelorMittal Maizieres Research SA, Voie Romaine-BP30320, 57283 Maizières-lès-Metz, France; Centro Ricerche Fiat, Corso Settembrini 40, Porta 8, Corpo 1, 10135 Torino, Italy; Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, Abstract: In this work, a medium Mn-Ni steel was treated through Quenching and Partitioning (Q&P) with a partitioning temperature (PT) of 650 ◦ C, which corresponded to the start of the austenite reverse transformation (ART) phenomenon
The red trace portion of the curves corresponds to the heating from quenching temperature (QT) to PT, maintaining at PT for the defined partitioning time (Pt) and the final cooling to room temperature
This was true for both partitioning time conditions and agrees with the previously described higher contraction observed in dilatometry curves in the QT15 condition and the results reported in [29]

Summary

Introduction

The influence of the quenching temperature (QT) and partitioning time (Pt) on austenite stabilization and mechanical properties was investigated. Mn steels (MMnS) are considered the most promising candidates These steels are able to simultaneously provide high strength and ductility, which is needed for the reduction of vehicles’ weight and increased passenger safety [1,2]. Both are multiphase steels containing a high amount of retained austenite (RA) in their microstructures. Considering typical retained austenite fractions of 0.05–0.10 and a low fraction of fresh martensite, the yield ratio is rather high, which represents a clear advantage in terms of safety and localized deformation performance, such as during hole expansion tests [14,15]

Objectives

Methods

Results

Discussion

Conclusion