Effect of Warm to Hot Rolling on Microstructure, Texture and Mechanical Properties of an Advanced Medium-Mn Steel
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TRODUCTION
HIGH-MN structural steels have aroused a great interest among material scientists and mechanical engineers.[1–3] Such special attention has been caused by a beneficial combination of mechanical properties of these materials, namely high strength along with high ductility, owing to so-called twinning-induced plasticity (TWIP) or transformation-induced plasticity (TRIP) effects. The latter is associated with e-martensitic transformation. The TWIP effect in austenitic steels can be expected, when the stacking fault energy (SFE) value lies between about 20 to 50 mJ/m2, whereas the TRIP effect occurs at lower SFE values.[4] An appropriate value of SFE is commonly achieved by alloying with a high amount of manganese (18 to 30 pct), and carbon (0.2 to 0.6 pct).[4,5] Aluminum and silicon are also sometimes used as alloying supplements for high-Mn austenitic TWIP steels to adjust SFE, provide desirable solution strengthening, and suppress delayed fracture.[6–8] The alloying design that involves high manganese percentage MARINA TIKHONOVA, VLADIMIR TORGANCHUK, ANDREY BELYAKOV, and RUSTAM KAIBYSHEV are with the Belgorod State University, Belgorod 308015, Russia. Contact e-mail: [email protected] FREDERIKE BRASCHE and DMITRI A. MOLODOV are with the Institute of Physical Metallurgy and Metal Physics, RWTH Aachen University, Aachen 52074, Germany. Manuscript submitted February 5, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
causes a relatively high cost of the steel production that is one of the main disadvantages of high-Mn TWIP steels. Currently, medium-Mn steels are considered as an alternative to high-Mn steels.[9] They are relatively cheap and can offer an improved combination of mechanical properties under certain conditions.[10–13] It is generally agreed that both high strength and plasticity in high-to-medium-Mn steels is governed by the austenitic phase, which exhibits TWIP or TRIP effects depending on SFE and austenite stability.[9,14,15] Thus, an increase in austenite fraction should be favorable for the mechanical properties of medium-Mn steels. On the other hand, the austenite should have an appropriate SFE and should be rather stable against a¢-martensitic transformation, which is much less effective for the strain hardening than e-martensitic transformation. In the case of medium-Mn steel containing 5 to 10 pct Mn, enhanced mechanical properties are achieved by intercritical annealing in the two phase (austenite-ferrite) region, when the redistribution of alloying elements (mainly carbon) provides an appropriate combination of austenite fraction and properties.[16–18] Both the fraction and stability of austenite increase with an increase in manganese and carbon content. Almost single phase austenitic steel can be obtained by alloying with 12 pct Mn and 0.6 pct C.[19] Such steel, i.e., Fe-12 pct Mn-0.6 pct C, should combine a relatively low price of medium-Mn two-phase austenitic-ferritic steels and
improved mechanical properties of high-Mn austenitic steels. This price-property compromise advances the
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