Regular Article

Influence of the size of the prior β grains on the microstructure of β quenched Zircaloy-4

¹ Institut Préparatoire aux Études d’Ingénieurs de Nabeul (IPEIN), Campus Universitaire, Merazka, 8000 Nabeul, Tunisie
² Centre SMS, Laboratoire Georges Friedel, UMR CNRS n o 5307, École Nationale Supérieure des Mines de Saint-Étienne, 158 cours Fauriel, CS 62362, 42023 Saint-Étienne Cedex 2, France

^* e-mail: yamen_benammar@yahoo.fr

Received: 7 February 2018
Accepted: 4 October 2018

Abstract

This work deals with the influence on Zircaloy-4 of annealing in the β domain and subsequent quenching in view of extrusion. The effect of the size of the prior β grains on the microstructure is investigated. The results indicate that for prior β grain sizes up to 1.6 mm, the β quenched Widmanstätten microstructure is distributed between “parallel platelets” and “basket-weave”. However, sizes larger than 2 mm promote the formation of “basket-weave”. Double annealing in the β domain leads to the formation of large prior β grains with no need to anneal for a long time. Indeed, protracted annealing may lead to exaggerated growth. Efficient double annealing requires some conditions: rate of cooling after the first β annealing a few °C.s⁻¹ (air cooling), heating rates of 1 or 2 °C.s⁻¹ during the second rise in temperature. The second cooling should be somewhat quicker (possibly 12 °C.s⁻¹ and above) to obtain the thin, intricate lamellae favored for extrusion.