Study of the Effect of Microalloying on Microstructure and Mechanical Property Formation for Rolled Product of Strength
- PDF / 3,915,119 Bytes
- 11 Pages / 594 x 792 pts Page_size
- 58 Downloads / 194 Views
STUDY OF THE EFFECT OF MICROALLOYING ON MICROSTRUCTURE AND MECHANICAL PROPERTY FORMATION FOR ROLLED PRODUCT OF STRENGTH CLASS K52 PRODUCED UNDER CRU CONDITIONS V. V. Naumenko,1 O. A. Bagmet,2 M. Yu. Matrosov,3 A. V. Muntin,4 E. A. Soldatov,5 and A. A. Kichkina3
UDC 669.14.018.41
Results are provided for a study of the effect of different microalloying systems (Nb, Nb–V, V–N) on structure formation and mechanical properties of rolled product of strength class K52 produced by combined technology of melting, casting of thin slabs 90 mm thick, and direct rolling with subsequent accelerated cooling and winding on a coil. It is shown that all of the micro-alloying versions selected provide the required strength properties, while metal microalloyed solely with niobium demonstrates the best brittle fracture resistance at low temperature. It is shown that addition of niobium to steel not only refines grain size in the metal matrix, but also changes ferrite morphology increasing the proportion of acicular ferrite, which improves steel cold resistance. Keywords: casting and rolling unit (CRU), low-carbon micro-alloyed steels, strengthening mechanisms, microstructure, precipitates, mechanical properties.
Achievement of the required level of strength properties of contemporary steels for pipes may be realized by such methods as thermomechanical treatment (TMT) and addition of alloying/microalloying elements in a certain ratio [1, 2]. It is well known [3] that the main task of microalloying steel subjected to TMT includes action on structure formation processes in different stages of the production process with the aim of obtaining two other types of structure even before austenite transformation: recrystallized fine-grained or deformed with a high effective specific surface. In the first case the main task is expansion of the field for occurrence of complete austenite recrystallization and retardation of recrystallized grain growth, and in the second in contrast it is expansion of the region of recrystallization retardation [4]. In this case steel microalloying makes it possible to improve metal strength properties by a precipitation hardening mechanism [5]. The AO Vyksa Metallurgical Plant (AO VMZ) specializes in the production of straight-seam electrically welded pipes including those from in-house rolled product that is prepared under conditions of a casting and rolling unit (CRU) by contemporary technology: melting, thin slab casting, direct rolling followed by accelerated cooling, and winding on a coil [6]. The existing concept of chemical composition for rolled product manufacture under CRU conditions is microalloying steel solely with niobium in order to achieve the required set of mechanical properties [7]. In this case alternative versions of microalloying are also considered [8–10]. Price instability for niobium and vanadium in world markets requires metal product manufacturers to consider immediately several microalloying schemes making it possible to obtain the required strength properties in 1 2 3 4 5
AO Vyksa Me
Data Loading...
