Influence d’une addition de vanadium sur le comportement structural d’aciers du type Z80CDSV8.2

Influence of a vanadium addition on the structural behaviour of steels Z80CDSV8.2 type

Laboratoire de Structure des Matériaux Métalliques, Université Paris Sud, Centre d'Orsay

Abstract

New grades of Cr-Mo-Si steels (0.8wt% C) with a specific addition of Vanadium, liable to substitute for conventional materials like chromium steels or cast irons in manufacturing cylinders for hot rollers, have been characterized from the structural point of view. In the as-received state, different types of carbides (M₂₃C₆ , M₇C₃ and MC) have been identified; therefore, a preliminary study of their partial solution between 1000 and 1200°C had led to choose an austenizing temperature of 1050°C in order to keep a small grain size and reduce the amount of residual austenite after quenching to room temperature.

During continuous cooling, the first change in the parent phase is a Vanadium carbide (M’C) precipitation for rates smaller than 9°C/s; this precipitation becomes impressive for rates less than 0.10°C/s which then enhances the formation of bainite and/or ferrite. The comparison of CCT diagrams for two V content (0.85 and 2 wt%) shows mainly that an increasing amount of vanadium reduces the critical quenching rate, favours the carbide precipitation as well as the ferrite formation and also slightly increases M_s. Phase transformations developed by interrupted quenching are characterized by a gap between the domains in which the parent phase respectively led to M’C carbides then to ferrite/perlite or to M₃C carbides then to bainite (this transformation been unfulfilled even after 10 h or more). The comparison of TTT diagrams drawn for both steels shows chiefly that an increasing amount of Vanadium tends to shorten incubation times for the various transformations.