Thermomechanical Processing of Fe-6.9Al-2Cr-0.88C Steel: Intercritical Annealing Followed by Quench Tempering
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DUCTION
ALTHOUGH the physical properties, mechanical behavior, and corrosion resistance of iron aluminide (Fe3Al and FeAl) have been extensively studied in past decades, only a few studies have been aimed at understanding and improving the ductility of these alloys as discussed by Hawk and Alman[1]; as discussed elsewhere.[2–6] Iron aluminide exhibits outstanding wear resistance, high hardness, high elastic modulus, and good environmental resistance; therefore, they are promising materials for different uses particularly in aggressive environments as discussed by Farahat, ElBadry[3]; Hwanga et al.[7–9] It has been shown by Hawk and Alman[1] that Fe3Al has wear resistance similar to those of a variety of steels such as 304 SS and 316 SS and they also found that the addition of Ti to Fe3Al has a positive influence on the tribological properties as discussed by Ryu et al.[10] However, a previous work has shown that different cooling rates of iron aluminide have little effect on their room-temperature ductility which makes the processing and machining of materials very difficult as discussed by Farahat, El-Badry.[3] Therefore, this paper is a trial to enhance the room temperature strength and ductility via intercritical annealing and subsequent quenching, (tempering process to generate retained austenite) to obtain the TRIP effect to be used in automotive industries and different suitable applications (Figure 1).
II.
EXPERIMENTAL WORK
The chemical composition (in weight pct) of the used steel in this study is listed in Table I. According to Al content; the critical transformation temperatures of steel can be predicted. Figure 2 demonstrates the actual critical transformation temperatures using quench type dilatometer (see Figure 2(a)). The steel was intercritically annealed at different temperatures from 1183 (910) up to 1283 K (1010 °C) for 15 minutes and subsequent quenched (tempered) at 623 K (350 °C) for 10 minutes to enhance the ductility as shown in Figures 2(b) and (c). Microscopic observation was carried out for hot forged and heat-treated specimens using Meiji-MX8500 optical microscope. A. Compression Tests Compression specimens were machined according to ASTM standard E-8. The ASM Handbook states that axial compression testing is a useful procedure for measuring the plastic flow behavior and ductile fracture limits of a material. Axial compression testing is also useful for measurement of elastic and compressive fracture properties of brittle materials or low-ductility materials. In any case, the use of specimens having large L/D ratios should be avoided to prevent buckling and shearing modes of deformation. Therefore, the L/D ratio taken in this paper is equal to 2. B. X-ray Diffraction
AHMED ISMAIL ZAKY FARAHAT, Associate Professor, is with the Plastic Deformation Department, Central Metallurgical Research and Development Institute, P.O.Box 87, Helwan, Cairo, Egypt. MASOUD IBRAHIM MOHAMED, Associate Professor, is with the Chemical and Material Engineering Department, Faculty of Engineering, Northern Border Univers
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