Fretting corrosion in liquid lead of structural steels for lead-cooled nuclear systems: Preliminary study of the influence of temperature and time

Abstract

Structural materials development is a key issue for the realization of advanced lead cooled nuclear systems. One specific challenge for fuel claddings and heat exchanger tubes is the so called fretting corrosion by flow induced vibrations. To address this matter, the ferritic–martensitic steel T91 and the austenitic steel 1.4970 were submitted to fretting corrosion test in liquid lead. Preliminary indications concerning the role of temperature and time/number of cycles in the fretting corrosion process, were achieved performing fretting corrosion tests at 450/500°C and for 150/600h (5.4×106/2.16×107cycles). The interaction between fretting (mechanical wear) and corrosion processes (oxidation/dissolution) in liquid lead was also investigated.The experiments revealed that protective oxide scales that formed on steels surfaces are removed by the fretting action. Thus, dissolution attack can take place. Besides, in the fretted areas, the formation of interposing layers was noticed. Such scales, created by debris retention and compaction, consist of an outer layer of oxidized debris and an inner layer of metallic debris. Due to the high Ni content, fretting corrosion affects more significantly the 1.4970 than the T91. Moreover after the 600h test, fatigue cracking was observed on the 1.4970. The volume of material removed from the specimens by fretting corrosion, increased with temperature and time respectively number of cycles.