• PDF / 1,634,467 Bytes
• 5 Pages / 593.972 x 792 pts Page_size
• 89 Downloads / 230 Views

DOWNLOAD

REPORT

---

h-Mn austenitic steels exhibiting the twinninginduced plasticity (TWIP) effect have been arousing a great interest among materials scientists because of their superior strain-hardening ability resulting in excellent combination of strength and ductility.[1] A little common disadvantage of high-Mn TWIP steels is their relatively low yield strength, which restricts certain applications requiring enhanced strength properties. There are two general approaches to increase the yield strength of definite steel or alloy. These are the dislocation strengthening and the grain size strengthening.[2–4] The dislocation strengthening of TWIP steels can be easily achieved by a cold-to-warm working; their pronounced work hardening gives a unique possibility to obtain the semi-product with desired strength level.[5] On the other hand, cold working followed by a recrystallization annealing can be used for grain refinement leading to strengthening in accordance with

PAVEL KUSAKIN, Research Associate, RUSTAM KAIBYSHEV, Professor, and ANDREY BELYAKOV, Leading Research Associate, are with Belgorod State University, Belgorod, 308015, Russia. Contact e-mail: [email protected] KANEAKI TSUZAKI, Professor, is with Kyushu University, Fukuoka, 819-0395, Japan. DMITRI A. MOLODOV, Professor, is with the Institute of Physical Metallurgy and Metal Physics, RWTH Aachen, 52056, Aachen, Germany. Manuscript submitted May 23, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A

Hall–Petch relationship.[6] The strengthening of high-Mn TWIP steels by cold rolling and annealing has been a subject of a number of papers.[4,6–10] The grain refinement affects significantly the dislocation substructure formed upon straining that controls the evolution of lamellar twin substructure.[11] A decrease in the grain size to several microns promotes significantly the work hardening capacity,[12] whereas further grain refinement down to submicron range tends to suppress the deformation twinning.[13] Cold working brings about high dislocation densities and the development of deformation twinning. The latter provides substantial strengthening but it is accompanied with undesirable fall of plasticity, which approaches almost zero as the twinning exhausts.[5,14] A beneficial combination of strength and plasticity can be achieved when the strengthened steel possesses the ability to further twinning. This can be realized under conditions of warm working, which is not accompanied by an extensive deformation twinning and, therefore, can provide the strain hardening and preserve the TWIP effect. One of the most effective and simple warm working techniques is the multiple multi-axial forging.[15] In this case, the homogeneous evolution of dense dislocation substructures is associated with the sequential change in the forging direction in each forging pass that promotes the operation of various slip systems. The aim of the present paper is to report the results of our current comparative study on the efficiency of dislocation strengthening and grain size strengthening of a high-Mn TWIP steel su