Relationship between Microstructures and Tensile Properties of an Fe-30Mn-8.5Al-2.0C Alloy

Abstract

Owing to the presence of a large amount of fine (Fe,Mn) 3 AlC carbides within austenite () matrix, the tensile property of the Fe-30%Mn-8.5Al%-2.0%C (in mass%) alloy in the as-quenched condition was clearly superior to that of the as-quenched FeMnAlC (C 5 1:3%) alloys investigated by previous workers. After being aged at 823 K for 3 h, the present alloy could possess high yield strength up to 1262 MPa with an excellent 32.5% elongation. With almost equivalent ductility, the yield strength obtained was about 16% higher than that of the FeMnAlC (C 5 1:3%) alloys after solution heat-treatment or controlled-rolling followed by an optimal aging at 823 K. Additionally, due to the pre-existing fine (Fe,Mn) 3 AlC carbides within the matrix in the as-quenched alloy, the aging time required for attaining the optimal combination of strength and ductility was much less than that of the FeMnAlC (C 5 1:3%) alloys aged at 823 K. When the present alloy was aged at 823 K for a time period longer than 4 h, both the strength and ductility were drastically dropped due to the occurrence of o = ( o : carbon-deficient austenite) lamellar structure on the = grain boundaries.

A Review on Nano-Scale Precipitation in Steels

“…It should also be noted that the drop of yield strength after the peak strength increment does not necessarily mean that the precipitates are overaged and Orowan looping takes place. Grain boundary precipitation that weakens the grain boundaries can also contribute to a loss of yield strength [26]. Orowan looping mechanism also does not mean a strength reduction, as Gutierrez-Urrutia and Raabe [27] and Sun et al [39] showed a great Orowan strengthening but at a great expense of ductility.…”

“…This is not necessarily to be the case. Haase et al [7], Chooi et al [50], and Lin et al [26] reported great ductility (~55%) in the quenched and homogenized austenitic Iron-Manganese-Aluminium-Carbon (Fe-Mn-Al-C) steels that contain a low volume fraction of fine shearable κ-carbides. After aging, the ductility reduces with the increasing volume fraction and size of κ-carbides [7].…”

“…In general, the coarsening of precipitates is proportional to interfacial energy, solubility limit, and the diffusivity of the solutes or precipitates [67]. [17] TiC [29] (Ti,Mo)C [29] Cu [33] TiC [53] K carbide [26] NiAl [25,39] (a) …”

“…Nano-scale precipitates can be obtained through nucleation [3,4,15,35] or spinodal decomposition [7,26,50]. Most of the steels [2][3][4]35] with a high number density (in the order of 10 24 m −3 ) of nano-scale precipitates were developed based on the theory of nucleation.…”

“…A compilation of (a) yield strength increment and (b) ductility change against precipitate number density of various precipitate strengthened steels. TiC [40] Ni3Ti [14] Cu + NiAl -4%Ni [1] Cu + NiAl -2.5%Ni [1] NiAl -3%Mn [2] NiAl -no Mn [2] NiAl [3] Cu + NiAl [15] Cu + (Ti,Mo)C [16] (Ti,Mo)C [16] Cu + M2C [17] TiC [29] (Ti,Mo)C [29] Cu [33] K carbide [26] k carbide [7] Cu -no Ni [4] Cu -0.75%Ni [4] k carbide [27] NiAl [39] (a)…”