ABSTRACT

The stress corrosion cracking (SCC) susceptibility of 30Cr2Ni4MoV rotor steel welded joint in a 3.5 wt.% NaCl solution at 180 °C was investigated using slow strain rate tensile (SSRT) tests at different strain rates. The result revealed a significant reduction of ductility with slower strain rates, but little effect of strain rate on tensile strength was observed. The reduction in area decreased and the percentage of SCC area on the fracture surface increased with the strain rate decreasing, which indicated higher SCC susceptibility. Although the strain rates greatly influenced the SCC behavior in the welded joint, all the specimens fractured in nearly the same position of the weld metal (WM). This is likely to be ascribed to the lowest strength limit in WM among the welded joint and the SSRT tests with the strain rate of 10-7 s-1 are still dominated by mechanical factor.

INTRODUCTION

Nuclear steam turbine is one of the critical parts in the nuclear power plant. With the increasing power capacity of power plants, the rotor geometry is increased at the same time which brings some trouble to process and manufacture. Advanced welding technology has become a critical method for manufacture of large steam turbine rotor in practice. Nevertheless, the appearance of stress corrosion cracking (SCC) is a potential risk for the welded rotor due to the effect of complicated chemical compositions, inhomogeneous microstructures and mechanical properties of welded joint 1,2. With the increasing power capacity of power plants, it is difficult to manufacture the nuclear steam turbine rotor over 1000MW through the total forging process. As one of the easier and more feasible manufacturing methods, welding process not only simplify procedures of forging but also welded rotors work stability in operation. However, the non-uniform distribution of microstructures and chemical elements are introduced by the multi-welding process with high temperature, which may lead to galvanic corrosion when welded joints are immersed in the corrosive environment 3.

This content is only available via PDF.
You can access this article if you purchase or spend a download.