Formation of BCC martensite in the stable FCC materials under severe plastic deformation

Borys M. Efros 2Anatolii I. Deryagin 1Natalya B. Efros 2V. P. Pilyugin 1

1. Russian Academy of Sciences, Ural Division, Institute of Metal Physics, 18 S.Kovalevskaya str., GSP-170, Ekaterinburg 620219, Russian Federation
2. National Academy of Sciences of Ukraine, A.Galkin Donetsk Institute for Physics & Technology (DonPTI NASU), Roza Luxemburg 72, Donetsk 83114, Ukraine

Abstract

Stable austenitic steels are not prone to formation of a strain-induced martensite and do not experience FCC-BCC transformations during high-temperature annealing.
Some alloyed Fe-Mn steels with FCC phase (austenite structure) were examined by the balance magnetometer and transmission electron microscopic methods. It was shown that nearly 0.01% of a fine BCC phase was formed in the Hadfield (Fe85.8Mn13C1.2) steel after a cold plastic deformation to epsilon = 50%. The BCC phase had crystallites ~ 200 nm in size, which did not allow identifying it by transmission electron microscopic methods. The presence of BCC phase nucleation centers in the deformed steel constrain reduced of the temperature of the precipitation austenite by 180 oC.
Fine crystals of a BCC martensite nearly 30 nm in size, whose concentration was as high as ~2.3%, were detected in an austenitic steel Fe79.5Mn17Al3C0.5 after a cold plastic deformation to epsilon = 95%. Those crystals appeared in fragmented regions of a non-crystallographic shear band. As a result, the austenite decomposed during annealing at T = 500 C and about 45% ferrite was formed.
A high nitrogen-alloyed austenitic steel Fe61.3Cr18Mn20N0.7 contained 0.02 mass % fine crystals of a strain-induced BCC martensite 20 nm in size after a plastic deformation to epsilon = 30% at Tdef = -196C. The strain-induced martensite, which was formed under the given conditions, had an extremely low Curie temperature TC = 400C. When the steel was strongly deformed (e= 8) by shear under a high quasi-hydrostatic compression at room temperature, a strain-induced BCC martensite having a normal Curie temperature TC = 600C appeared and initiated a FCC-BCC transformation in the stable steel during annealing.

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Presentation: poster at E-MRS Fall Meeting 2004, Symposium I, by Borys M. Efros
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-04-24 07:18
Revised:   2009-06-08 12:55
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