Laves phase precipitation and its transformation kinetics in the ferritic stainless steel type AISI 441

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Authors

Sello, M.P.
Stumpf, Waldo E.

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Elsevier

Abstract

Electrolytic extraction followed by XRD analysis of precipitates after isothermal annealing of an AISI 441 ferritic stainless steel between 600 and 850 ◦C produced the time–temperature–precipitation (TTP) diagram for the Fe2Nb-Laves phase. The TTP diagram shows two classical C noses, the first one between 750 and 825 ◦C and the second one, estimated to be close to 650–675 ◦C. TEM analyses show two independent nucleation mechanisms, i.e. at about 600 ◦C nucleation takes place on dislocations but above 750 ◦C, grain boundary nucleation is dominant. The measured solvus temperature of 875 ◦C for Fe2Nb in this steel is 50 ◦C higher than predicted by Thermo-Calc®. Kinetic modelling at 800 ◦C agreed well with the experimental results for a surface energy of 0.435 J m−2 and an initial particle center-to-center separation distance on grain boundaries of about 0.2 m.

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Keywords

Laves phase (Fe2Nb), Johnson–Mehl–Avrami–Kolmogorov (JMAK), Transformation kinetics, Laves phase precipitation, Ferritic stainless steel type AISI 441, Time–temperature–precipitation (TTP)

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Citation

Sello, MP & Stumpf, WE 2011, 'Laves phase precipitation and its transformation kinetics in the ferritic stainless steel type AISI 441', Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing, vol. 528, no. 3, pp. 1840-1847.