title: Three-dimensional atom probe characterization of alloy element partitioning in cementite during tempering of alloy steel.
abstract: Hardness measurements confirm that the martensitic microstructure of an alloy steel, AISI/SAE 4340, is significantly more resistant to softening, compared to the martensitic microstructure of a high-purity Fe-0.4% C alloy, at tempering temperatures, 300-400 degrees C, just above the temperatures where cementite replaces transition carbides in the martensitic matrix. Three-dimensional atom probe (3DAP) analyses of the 4340 steel show that Si rejection from the cementite is first detected after low-temperature tempering for times of 1 h. After 10-h tempering at 400 degrees C, Mn and Cr contents are increased, and Ni contents decreased, in cementite according to their carbide- and non-carbide-forming tendencies, respectively. The results are discussed with respect to the diffusivity of the substitutional alloying elements in the 4340 steel, and the effect that such diffusion-controlled redistribution would have on maintaining fine distributions of cementite that resist softening during tempering.
authors: Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK.
authors: Chen
authors: C
authors: Zhu
authors: X Y
authors: XY
authors: Xiong
authors: A
authors: A
authors: Cerezo
authors: R
authors: R
authors: Hardwicke
authors: G
authors: G
authors: Krauss
authors: G D W
authors: GD
authors: Smith