Study On Bauschinger Effect Of Zircaloy-4 During Cyclic Deformation

Zircaloy-4 is generally used as fuel tubes in pressurized water reactors because of it' s low neutron absorption cross-section, excellent corrosion resistance, good strength and ductility. In practical application, it is subjected to local plastic strain cycles due to the power fluctuations during reactor operation; Extremely, this power fluctuations could lead fatigue failure. So it is very important to understand the cyclic deformation behavior of Zircaloy-4.In this paper, Bauschinger effect of Zircaloy-4 with different metallurgical state at room temperature and 400癈 is investigated in an incremental step test and cyclic deformation test under constant strain control. Bauschinger effect during cyclic deformation is described by using back stress, which is mainly responsible for Bauschinger effect; Back stress is attained by using KWL' s method.The experimental results is shown as followings:(1) The cyclic flow stress-strain curves in an incremental step test could be expressed as the power law relation:(2) When the strain amplitude is lower during cyclic deformation tests under constant strain control, softening firstly appears, then gradually hardens with the increasing numbers of cycle; When the strain amplitude is higher, hardening firstly appears, then gradually softens. While cyclicdeformation experiment under constant strain control is performed in 400℃, the material shows the continuous hardening until cyclic invalidation.(3) Back stress attained by KWL' s method is used to analyse the Bauschinger effect during an incremental step cyclic test and cyclic deformation test under constant strain control, it is shown that back stress increases with increasing plastic strain and the numbers of cycle, and the back stress is uniform, regardless of tension or compression conditions.(4) As far as recrystallized Zircaloy-4 plate is concerned, the back stress in transverse direction is higher than that in rolling direction due to the higher Schmid factor in Rolling direction.(5) Comparing with room temperature, back stress at 400℃ is lower.(6) Hydrogen in Zircaloy-4(200μg/g) has not apparent influence on back stress.(7) After β treatment, back stress of Zircaloy-4 will vary, and is higher than that of pre-treatment at the higher plastic strain.