Metallurgical Phase Transformation and Behavior of Steels Under Impact Loading
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DUE to its good mechanical, chemical, and physical properties, stainless steel is widely employed in many sectors of industry. Several classes of this material have been developed for various applications and are used in daily life. In the present study, we deal with a certain type of stainless steel which is characterized by the transformation-induced plasticity (TRIP) effect.[1] This stainless steel is usually employed in safety-critical parts like hinges, as well as in stiffeners of complex shapes. Gala´n et al.[2] assessed that TRIP steel are good choice for crash performance due to their excellent energy absorption ability, high strain-hardening rates, high mechanical strength combined to a strong bake hardening effect. So, these steels are used in structural and reinforcement parts of complex shape, cross members, longitudinal beams, sills, and bumper reinforcements in automotive.[3] The TRIP phenomenon corresponds to the transformation of austenite to martensite under the effect of mechanical loading, heating, or both. Zackay et al.[4]
M. ZEROUKI and M. OULD OUALI are with the Laboratoire E´laboration et Caracte´risation des Mate´riaux et Mode´lisation (LEC2M), Universite´ Mouloud MAMMERI de Tizi-Ouzou, Tizi Ouzou, Algeria. L. BENABOU is with the LISV, Universite´ de Versailles Saint-Quentin-en-Yvelines, Paris Saclay, France. Contact email: [email protected] Manuscript submitted June 4, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
attribute the high strain-hardening rate of TRIP steels to the deformation of the hard second-phase martensite dispersed in the soft ferrite matrix as well as to the transformation of retained austenite to martensite which increases the hardening rate at higher strain levels during deformation. The ductile austenitic matrix, containing lath martensite after the phase transformation, has not only a greater elongation at rupture but also a greater strength. The plastic strain originating from the martensitic transformation is referred to as transformation plasticity.[5–7] This form of plasticity contributes remarkably to the mechanical properties of this class of stainless steels by improving their ductility, strength, strain-hardening capacity, and delays the occurrence of necking.[8–10] Sachedv[11] studied the effect of residual austenite on the tensile behavior of a dual phase steel at temperatures between 50 C and 187 C, suggesting that the ductility of dual phase steels can be further improved by optimizing the stability of the retained austenite. Authors[12–14] concluded that the rate of transformation of retained austenite and thus, its mechanical stability are the key factors that influence the work hardening behavior of TRIP-assisted steels. Olson and co-workers[15–19] studied the mechanism of the strain-induced nucleation of martensitic transformations and its effect on the overall behavior of material. They proposed a numerical model for transformation plasticity accompanying strain-induced martensitic transformations in metastable austenitic steels.
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