Low cycle fatigue behaviour of AISI 308 stainless steel weld metal

Abstract

Dissimilar metal welds (DMW) are widely employed to meet various fabrication
requirements in the integrated structures. In advanced heavy water reactors (AHWR),
main heat transport (MHT) piping system is made of austenitic stainless steels (SS) and
the later part of the piping is often made of carbon steels mainly to reduce the overall cost
of the structure. These two metals (austenitic and carbon steels) are joined by DMW
using SS 308 electrode. The operating temperature of this structure varies from 25-285
°C. This fluctuation in temperature causes thermally induced elastic-plastic strain
reversals.
In the present investigation an attempt has been made to study the low cycle fatigue
(LCF) behaviour of AISI 308 stainless steel weld metal. All LCF tests were conducted at
ambient condition following the ASTM standard E-606[1]. These tests were conducted at
strain amplitudes of 0.5%, 0.7%, 1.0%, 1.2% and 1.5% under fully reversed cycles
(R=-1).
Various approaches such as (i) strain, (ii) energy, (iii) cyclic stress-strain curve (CSSC)
and (iv) master curve have been employed in this investigation[2]. Walker and Smith
Watson Topper (SWT) life estimation models have also been attempted in the present
study[3]. The experimental results indicate pronounced Bauschinger effect, softening
during lower strain amplitudes and Non Masing behaviour. Comparison of cyclic stressstrain
curve (CSSC) and monotonic stress strain curve (MSSC) shows complex
hardening-softening behaviour. It is also known that plastic strain (Δεp) is the
predominant cause of energy dissipation during low cycle fatigue[4]. The plastic strain
energy calculated from the experimental data and estimated using constitutive equation
follows linear relationship with strain amplitude. This however remains constant when
plotted as a function of number of cycles to failure. The observations exhibit that Walker
and SWT fatigue life prediction models hold well in predicting fatigue life of the present
material.