Title: The microstructures evolution and composition shift of ZGCr30Ni20NRE steel at carburising atmosphere

Authors: Xinmin Luo, Jinlan Wang, Kangmin Chen

Addresses: School of Material Science and Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang, Jiangsu 212013, P.R. China. ' School of Material Science and Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang, Jiangsu 212013, P.R. China. ' School of Material Science and Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang, Jiangsu 212013, P.R. China

Abstract: By means of scanning electronic microscopy (SEM), EDS and X-ray diffraction, the microstructures evolution and the composition shift of austenitic steel ZGCr30Ni20NRE at the carburising atmosphere were investigated. The experimental results showed that the continuous penetration of the active carbon atoms broke the thermodynamic equilibrium in the steel and caused the redistribution of the alloying elements. It is revealed that the chromium (Cr) content in M₇C₃ increased to 48.84%, whereas only 2.89% remained in austenite; and nickel (Ni) shifted into austenite to 41.67%, but 4.37% remained in carbide. This composition shift resulted in Cr dilution of the austenite, and the progressive growth of the M₇C₃ carbide, reaching over 50μm in diameter. The oxygen invasion in opposite direction resulted in the interior porous and the oxidised cavities. Consequently, it is most important for the radiant tube made of the steel to obtain anti-carburising on its outer surface and antioxidising performances on its inner surface respectively.

Keywords: austenitic steel; chemical composition; nickel; chromium; microstructure; M7C3 carbide; carburisation; radiant tubes; furnaces; failure analysis; oxidation.

DOI: 10.1504/IJMMP.2009.031396

International Journal of Microstructure and Materials Properties, 2009 Vol.4 No.4, pp.412 - 422

Published online: 02 Feb 2010 *

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