Microstructural evolution during the austenite-to-ferrite transformation from deformed austenite

Journal Article · Sun Feb 01 04:00:00 EST 1998 · Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science

DOI:https://doi.org/10.1007/s11661-998-0122-1· OSTI ID:611575

Bengochea, R ^[1]; Lopez, B; Gutierrez, I ^[1]

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1. CEIT, San Sebastian (Spain). Dept. of Materials

It is well established that the ferrite grain size of low-carbon steel can be refined by hot rolling of the austenite at temperatures below the nonrecrystallization temperature (T{sub nr}). The strain retained in the austenite increases the number of ferrite nuclei present in the initial stages of transformation. In this work, a C-Mn-Nb steel has been heavily deformed by torsion at temperatures below the determined T{sub nr} for this steel. After deformation, specimens are cooled at a constant cooling rate of 1 C/s, and interrupted quenching at different temperatures is used to observe different stages of transformation. The transformation kinetics and the evolution of the ferrite grain size have been analyzed. It has been shown that the stored energy due to the accumulated deformation is able to influence the nucleation for low undercoolings by acting on the driving force for transformation; this influence becomes negligible as the temperature decreases. At the early stages of transformation, it has been observed that the preferential nucleation sites of ferrite are the austenite grain boundaries. At the later stages, when impingement becomes important, ferrite coarsening accompanies the transformation and a significant reduction in the number of the ferrite grains per unit volume is observed. As a result, a wide range of ferrite grain sizes is present in the final microstructure, which can influence the mechanical properties of the steel.

• Sponsoring Organization: USDOE
• OSTI ID: 611575
• Journal Information: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 2 Vol. 29; ISSN 1073-5623; ISSN MMTAEB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CRYSTAL-PHASE TRANSFORMATIONS
DEFORMATION
GRAIN REFINEMENT
LOW ALLOY STEELS
MICROSTRUCTURE
THERMOMECHANICAL TREATMENTS