Abstract
In this paper, thermal cycles with different heat inputs and cooling rates were investigated for a novel lean duplex stainless steel 2002 using a welding simulation. The microstructure and pitting resistance of the simulated heat-affected zones were studied. With the increasing heat input, the amount and size of the austenite phase both increased, along with a transformation from rods to dendritic structures. The critical pitting temperature (CPT) and the pitting potential (Epit) both increased first and then declined as the heat input increased, indicating a strong dependence of pitting resistance on the heat input. For the different cooling rates, the amount of ferrite increased as the cooling rate increased from 0.25 °C/s to 20 °C/s. The CPT and Epit both increased with the increasing cooling rates, indicating an improved pitting resistance. The pits initiated preferentially at the boundaries of ferrite and austenite due to the precipitation of M23C6 in the specimens with different cooling rates.
Highlights
Duplex stainless steels (DSSs) have attracted much attention for the satisfactory mechanical properties and favorable corrosion resistance, which are widely used in chemical, petrochemical, and nuclear industries [1,2,3,4,5]
The dark austenite phase was embedded inside the gray ferrite matrix
The rod-like austenite phase appeared in the heat-affected zone (HAZ) for a low heat input
Summary
Duplex stainless steels (DSSs) have attracted much attention for the satisfactory mechanical properties and favorable corrosion resistance, which are widely used in chemical, petrochemical, and nuclear industries [1,2,3,4,5]. The microstructure, mechanical properties, and corrosion resistance of the welded metals strongly depend on the heat input, which affects the distribution of the main alloying elements of Cr, Mo, and N in the two phases. While for the low temperature HAZ, different cooling rates may cause a myriad of precipitates, such as the carbides (M23 C6 ), nitrides (Cr2 N), and intermetallic phases (σ, χ), affecting the corrosion properties of steel [26,27,28,29,30]. It is essential to investigate the influence of different heat inputs and LTHAZ cooling rates on the microstructure and corrosion resistance of LDSS 2002. The welding thermal cycles with different heat inputs and LTHAZ cooling rates were performed on LDSS 2002 through a Gleeble thermomechanical simulator. The pitting resistance was evaluated using potentiodynamic polarization and critical pitting temperature (CPT) tests
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