Effects of martensite particle size and spatial distribution on work hardening behaviour of fine-grained dual-phase steel

ABSTRACT

Model dual-phase steel microstructural variants having fine ferrite grain size and a range of martensite particle sizes and spatial distributions were produced by varying the starting microstructure prior to the intercritical annealing treatment. Superior tensile properties were obtained for the microstructural variant having the smallest (∼1 µm) uniform ferrite grain structure and a corresponding uniform distribution of small (∼0.5 µm) martensite particles. This microstructural variant also exhibited superior work hardening properties, as determined from a Crussard–Jaoul analysis and plots of instantaneous work hardening exponent vs. strain. The true work hardening rate had a positive dependence on at low strain ( < 2%) for all three microstructural variants, consistent with the geometrically necessary dislocation mechanism. At higher strains, Stage III work hardening is operative and the dislocation annihilation factor exhibited a positive dependence on .

RÉSUMÉ

On a produit des variantes microstructurales modèles d’acier biphasé (DP) ayant une granulométrie fine en ferrite et une gamme de tailles de particules et de distributions spatiales de la martensite, en variant la microstructure de départ avant le traitement de recuit intercritique. On a obtenu des propriétés de traction supérieures pour la variante microstructurale ayant la plus petite (∼1 mm) structure uniforme de grain de ferrite et une distribution uniforme correspondante de petites (∼0.5 mm) particules de martensite. Cette variante microstructurale exhibait également des propriétés supérieures d’écrouissage, telles que déterminées à partir d’une analyse de Crussard-Jaoul et à partir de courbes de l’exposant instantané d’écrouissage en fonction de la déformation. La vraie vitesse d’écrouissage avait une dépendance positive sur (f/d)1/2 à faible déformation ([insert epsilon symbol here < 2%) pour les trois variantes microstructurales, compatible avec le mécanisme de dislocation géométriquement nécessaire (GND). Aux déformations plus élevées, l’écrouissage de Stage III est opératoire et le facteur d’annihilation de dislocation exhibait une dépendance positive sur (f/d)1/2.

KEYWORDS:

• Dual-phase steel
• work hardening
• ferrite grain size
• martensite particles

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

H. Seyedrezai is a Research Engineer at ArcelorMittal Global R&D – East Chicago. He is a graduate of Amirkabir University of Technology (B.Sc.), McMaster University (M.A.Sc.) and Queen's University (Ph.D.). His research expertise includes both steel and aluminum alloys, with a primary interest in structure–property relationships, phase transformations and new product design.

A. K. Pilkey is a Professor in the Department of Mechanical and Materials Engineering at Queen's University. He is a graduate of the University of Waterloo (B.A.Sc., M.A.Sc.) and Carleton University (Ph.D.). His research expertise encompasses structure–property relationships and the role of damage in the deformation and failure of materials, including steel and aluminum alloy grades used for automotive structural components as well as cancellous bone tissue.

J. D. Boyd is a Professor Emeritus in the Department of Mechanical and Materials Engineering at Queen's University. He is a graduate of the University of Toronto (B.A.Sc., Engineering Physics) and the University of Cambridge (Ph.D.). He has carried out research in private industry (Battelle), government (CANMET) and university (Queen's). His research is directed towards improving mechanical properties by microstructural design. It involves laboratory simulations of industrial processing and detailed characterization of microstructures and phase transformations. He has authored or co-authored over 200 refereed journal articles, conference papers and technical reports, and he is particularly known for his contributions to the physical metallurgy of microalloyed steels.

ORCID

H. Seyedrezai http://orcid.org/0000-0002-6040-0933

Additional information

Funding

The authors would like to acknowledge the financial support provided by the AUTO21 Network of Centres of Excellence (NCE) and the Natural Sciences and Engineering Research Council of Canada (NSERC).