Évolutions structurales associées aux traitements thermiques imposés à l’alliage Z 06 CND 17.04.02

Structural evolutions associated with the thermal treatments applied to Z 6 CND 17.04.02 alloyed steel

¹ Laboratoire de Métallurgie Structurale, Université Paris-Sud, Orsay.
² Laboratoire de Structure des Matériaux Métalliques, Université Paris-Sud, Orsay.

Abstract

The Z 06 CND 17-04-02 steel is used in the stream generators of nuclear reactors in the temperature range 500-520 °C. In the state referred to “as quenched” from 1100 °C, this steel consists of lath martensite and ≃ ferrite (with a volume fraction of = 18%). The present paper reports the study of the structural evolution of the steel occuring during thermal cycles performed betwenn 20 and 1200 °C with different heating and cooling rates varying from 50 to 0.02° C.s^–1. It aims first to precise the mechanism of the austenitic transformation as a function of the heating rate, secondly to determine the diagram obtained during continuous cooling from 1100 °C. The use of various and complementary experimental methods such as dilatometry, thermomagnetometry, X ray diffraction, transmission electron microscopy, EEDS analysis, hardness measurements... was necessary as an attempt to explain the complex phenomena which take place during the evolution of this steel.