Dynamically recrystallized austenitic grain in a low carbon advanced ultra-high strength steel (A-UHSS) microalloyed wit
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Dynamically recrystallized austenitic grain in a low carbon advanced ultra-high strength steel (A-UHSS) microalloyed with boron under hot deformation conditions I. Mejía1, E. García-Mora1, G. Altamirano1, A. Bedolla-Jacuinde1 and J. M. Cabrera2,3 1 Instituto de Investigaciones Metalúrgicas, Universidad Michoacana de San Nicolás de Hidalgo. Edificio “U”, Ciudad Universitaria, Morelia, Michoacán, México. 2 Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, ETSEIB – Universitat Politècnica de Catalunya. Av. Diagonal 647, Barcelona, Spain. 3 Fundació CTM Centre Tecnològic, Av. de las Bases de Manresa, 1, Manresa, Spain. ABSTRACT This research work studies the dynamically recrystallized austenitic grain size (Drec) in a new family of low carbon NiCrCuV advanced ultra-high strength steel (A-UHSS) microalloyed with boron under hot deformation conditions. For this purpose, uniaxial hot-compression tests are carried out in a low carbon A-UHSS microalloyed with different amounts of boron (14, 33, 82, 126 and 214 ppm) over a wide range of temperatures (950, 1000, 1050 and 1100°C) and constant true strain rates (103, 102 and 101 s1). Deformed samples are prepared and chemically etched with a saturated aqueous picric acid solution at 80°C in order to reveal the Drec and examined by light optical (LOM) and scanning electron microscopy (SEM). The Drec is related to the Zener-Hollomon parameter (Z), and thereafter the Drec divided by Burger's vector (b) is related to the steady state stress (ss) divided by the shear modulus () (Derby model). Results shown that the Drec in the current steels is fine ( 23 μm) and almost equiaxed, and the recrystallized grain size-flow stress relationship observed after of plastic deformation is consistent with the general formulation proposed by Derby. It is corroborated that boron additions to the current A-UHSS do not have meaningful influence on the Drec. INTRODUCTION Recent years have seen many developments in steel technology and manufacturing processes to build vehicles of reduced weight and increased safety. For this purpose, Advanced High Strength Steels (AHSS) have been developed. The AHSS include newer types of steels such as dual phase (DP), transformation-induced plasticity (TRIP), complex phase (CP), B steels (BS), and martensitic steels (MART), which are primarily multi-phase steels, and contain ferrite, martensite, bainite, and/or retained austenite in quantities sufficient to produce outstanding mechanical properties [1,2]. Researchers have studied the B effect in steels for a long time [3-7], particularly because of its potential to increase steel hardenability. Nowadays, B-bearing steels are extensively applied in the construction of heavy machinery, building structures, marine platforms and pipelines [8-11]. It is well-known that B atoms segregate towards austenite grain boundaries and increase hardenability of steel by suppressing the nucleation of ferrite [12]. The grain size is the only microstructural parameter that can simultaneously increase the strength
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