The effect of niobium on the microstructure and phase transformation kinetics in low-carbon Medium Manganese Steels

Patrick Peißl, Reinhold Schneider, Manfred Rahofer, Ludovic Samek, Enno Arenholz

Research output: Chapter in Book/Report/Conference proceedingsConference contribution

2 Citations (Scopus)

Abstract

Medium-Mn steels are a promising candidate to fulfil the requirements of the 3rd generation of AHSS (Advanced High Strength Steels) which combine high strength and high ductility. A new approach is to add micro alloying elements, like niobium, to affect microstructural development during recrystallization and phase transformations. Using a quenching dilatometer, the kinetics of the phase transformations from austenite (810 °C and 840 °C) to its transformation-products by varying different cooling rates (100 K/s to 0.03 K/s) were investigated for two low carbon medium-manganese steels with different contents of niobium. Based on the dilatometric curves, the results of light optical microscopy (LOM) and quantitative metallography, measurements of the retained austenite (RA) content by X-ray diffractometry (XRD) and hardness measurements, continuous-cooling-transformation (CCT) diagrams were constructed. Furthermore, the influence of the element niobium on the microstructure after intercritical annealing was investigated by similar methods. Different etching-methods (Nital, Klemm-I) were applied to reveal different microstructural aspects. Besides considerable grain-refinement effects with increased niobium content, the phase-transformations were accelerated in the CCT-diagrams. The microstructure varies from 100 % martensite to certain amounts of bainite, but also ferrite at lower cooling rates. Intercritical annealing results in different amounts of retained austenite.

Original languageEnglish
Title of host publicationEuropean Conference on Heat Treatment 2015 and 22nd IFHTSE Congress - Heat Treatment and Surface Engineering from Tradition to Innovation, 2015
Pages267-275
Number of pages9
Volume70
DOIs
Publication statusPublished - Dec 2015
EventEurop. Conf. on Heat Treatment 2015 & 22nd IFHTSE Congress - Venice, Italy
Duration: 20 May 201522 May 2015

Publication series

NameHTM - Journal of Heat Treatment and Materials
PublisherCarl Hanser Verlag GmbH & Co. KG
ISSN (Print)1867-2493

Conference

ConferenceEurop. Conf. on Heat Treatment 2015 & 22nd IFHTSE Congress
CountryItaly
CityVenice
Period20.05.201522.05.2015

Keywords

  • CCT-Diagrams
  • Dilatometry
  • Medium-Mn steels
  • Metallography
  • Niobium
  • Retained Austenite

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