kappa-carbide hardening in a low-density high-Al high-Mn multiphase steel

kappa-carbide hardening in a ferrite-austenite duplex low-density Fe-Mn-Al-C steel has been investigated as a function of annealing temperature in a range between 500 degrees C and 900 degrees C. Fine microstructure containing thin lamellar kappa-carbides in austenite and dispersed nano-scale particulate kappa-carbides in ferrite were formed in a temperature below 600 degrees C. This led to a high hardness. The steel was soften drastically at the higher annealing temperature. This is due to the formation of boundary kappa-carbides, discontinuous coarsened kappa-carbides, and spheroidized kappa-carbides. The kappa-carbides inside ferrite grain were transformed into austenite at 800 degrees C. The kappa-carbides within austenite grain were dissolved at 900 degrees C. The kappa-carbides are found to have a close to Nishiyama-Wasserman orientation relationship with the ferrite matrix. (C) 2014 Elsevier B.V. All rights reserved