Paper Title:

Effect of Bake-Hardening Treatment on the Mechanical Properties of High Strength Bainitic Steel Produced by Thermomechanical Processing

Periodical Materials Science Forum (Volumes 706 - 709)
Main Theme THERMEC 2011
Chapter Chapter 18: Steels
Edited by T. Chandra, M. Ionescu and D. Mantovani
Pages 2332-2337
DOI 10.4028/www.scientific.net/MSF.706-709.2332
Citation Ilana B. Timokhina et al., 2012, Materials Science Forum, 706-709, 2332
Online since January, 2012
Authors Ilana B. Timokhina, Hossein Beladi, Xiang Yuan Xiong, Peter D. Hodgson
Keywords APT, Bake-Hardening, Nanobainite, TEM, Thermomechanical Processing (TMP)
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The influence of pre-straining and bake-hardening on the mechanical properties of thermomechanically processed 0.2C-1.5Si-1.5Mn-0.2Mo-0.004Nb (wt%) steel was analysed using tensile test, transmission electron microscopy (TEM) and atom probe tomography (APT). This steel after processing had high strength (~1200MPa) and good ductility (~20%) due to the formation of fully bainitic microstructure with nanolayers of bainitic ferrite and retained austenite. The bake hardening (BH) of pre-strained (PS) samples increased the yield strength of steel up to 690MPa and showed the bake-hardening response of 220MPa due to the operation of several strengthening mechanisms such as transformation induced plasticity during pre-straining and pinning the dislocations by carbon during bake-hardening treatment. The carbon content of the bainitic ferrite and retained austenite before and after bake-hardening treatment, the solute distribution between these phases and the local composition of fine Fe-C clusters and particles formed during bake-hardening treatment was calculated using APT. The bainitic ferrite and retained austenite microstructural characteristics such as thickness of the layers and their dislocation density before and after bake-hardening treatment were studied using TEM.

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