The Effect of Fine M 2 C (M: Mo, Cr, Fe) Particles on the Recrystallization Temperature and High Temperature Strength of
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The Effect of Fine M2C (M: Mo, Cr, Fe) Particles on the Recrystallization Temperature and High Temperature Strength of Warm Rolled Fe3Al Based Alloys Satoru Kobayashi1 and Takayuki Takasugi2,1 1 Osaka Center for Industrial Materials Research, Institute of Materials Research, Tohoku University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan 2 Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho Naka-ku, Sakai, Osaka 599-8531, Japan ABSTRACT The effect of fine M2C particles on the recrystallization temperature and high temperature strength of warm rolled Fe3Al base alloys was investigated. Fe-27Al-1.2C-2Cr-xMo (x: 0.3, 0.9) alloys (in at.%) were arc melted, warm rolled and annealed. TEM observations have revealed that fine M2C particles were present in the alloy containing 0.9% Mo but not in the alloy with 0.3% Mo after warm rolling. The recrystallization temperature increased from 740 qC to 810 qC when the Mo content is increased from 0.3 to 0.9 due to the presence of fine M2C particles. Tensile tests conducted on annealed samples with fine sub-grained matrix have shown that the introduction of fine M2C particles is effective to enhance the proof stress at 600 qC. INTRODUCTION Fe3Al based alloys with the B2/D03- ordered structures have been regarded as potential high temperature structural materials due to their excellent resistance against oxidation and sulphidation at high temperatures [1], low materials costs and relatively low density compared with conventional stainless steels by ~15% [2, 3]. The research and development has been performed for many decades to improve their mechanical properties such as room-temperature ductility and high temperature strength. We have recently worked on thermomechanical processing (TMP) to achieve grain refinement of Fe3Al based alloys [4-6], and have found that the presence of N-Fe3AlC (E21) carbide particles in the matrix during warm rolling is effective in reducing the spacing of high angle boundaries and low angle boundaries in the matrix [7]. Warm rolled and annealed Fe3Al alloys with reduced grain (subgrain) sizes show high proof stress of ~700 MPa and reasonable ductility of ~8% in tensile tests at room temperature in air. Fine-grained microstructures are generally unstable against aging at high temperatures because of their high interfacial energy, and should therefore be stabilized to use the alloys as high temperature materials. One of the effective methods to stabilize fine-grained microstructures is to introduce fine second-phase particles to pin sub-boundaries and grain boundaries and thereby retarding recovery and recrystallization [8]. In the present study, the effect of fine M2C particles on the recrystallization temperature and high temperature strength of warm rolled Fe3Al base alloys was investigated.
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EXPERIMENTAL The nominal compositions of the alloys studied are listed in Table I. Hereafter the alloys will be referred to by their Mo content. The alloys were prepared from iron of 4N purity, a
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