The anisotropic kinetics of strain aging in a martensitic steel

ABSTRACT

An experimental study has been conducted to evaluate the effect of static strain aging (bake hardening) on the yield strength and yield strength asymmetry in torsion and torsion/reverse torsion tests on a low-carbon martensitic steel. It is shown that vastly different strain aging responses are observed in the forward and reverse portions of the torsion test following strain aging. While the yield stresses can be described phenomenologically by classic segregation kinetics, the observed asymmetry in the kinetics and magnitude of strain aging call into question the simple interpretation of dislocation de-pinning. This is further emphasised by the fact that strain aging modifies the apparent work hardening rate in the reverse loading tests.

RÉSUMÉ

On a effectué une étude expérimentale afin d’évaluer l’effet du vieillissement statique après transformation (durcissement par chauffage) sur la limite d’élasticité et sur la dissymétrie de la limite d’élasticité lors d’essais de torsion et de torsion renversée sur un acier martensitique à faible teneur en carbone. On observe des réponses très différentes du vieillissement après transformation des portions de torsion et de tension renversée de l’essai de torsion, suivant le vieillissement après transformation. Alors que l’on peut décrire phénoménologiquement la contrainte d’écoulement par la cinétique classique de ségrégation, la dissymétrie observée dans la cinétique ainsi que l’ordre de grandeur du vieillissement après transformation remettent en question l’interprétation simple du détachement de dislocation. Ceci est davantage mis en évidence par le fait que le vieillissement après transformation modifie la vitesse apparente d’écrouissage lors des essais de charge renversée.

KEYWORDS:

• Strain aging
• martensite
• Bauschinger effect
• torsion
• steel

Notes on contributors

Qingquan Lai was formerly a Post Doctoral fellow in the Department of Materials Engineering at the University of British Columbia is now researcher at Nanjing University of Science and Technology. He has interests in the the relationship between microstructure and mechanical properties in metallic alloys.

Chad W. Sinclair is a Professor in the Department of Materials Engineering at the University of British Columbia. He has interests in phase transformations and mechanical properties both from experiments and simulation.

Warren J. Poole is Professor and Head of the Department of Materials Engineering at the University of British Columbia. He holds the Rio Tinto Alcan Chair in Materials Process Engineering. His interests are in the area of process model development and experimental assessment of mechanical response.

Disclosure statement

No potential conflict of interest was reported by the authors.