Introduction
Weathering steel, also known as corten steel, is a high-strength low-alloy steel that is specially designed to resist atmospheric corrosion. It is often used in structural applications such as bridges, buildings, and outdoor sculptures. However, the corrosion resistance of weathering steel can be affected by various factors such as welding, microalloying, and environmental conditions. In this study, the influence of Cu and P microalloying on the corrosion resistance of A588 Grade B weathering steel plate welded joints was investigated.
Experimental Procedure
The experimental procedure involved preparing two types of A588 Grade B weathering steel plates with different microalloying elements. The first type of plate was the base metal, while the second type was the welded joint with Cu and P microalloying. The welded joint was prepared using gas tungsten arc welding (GTAW) with a filler metal of ER70S-6. The welding parameters were kept constant for all specimens.
The corrosion resistance of the specimens was evaluated using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in a 3.5 wt% NaCl solution. The EIS measurements were taken at an open-circuit potential with a frequency range of 10 kHz to 0.01 Hz. The potentiodynamic polarization tests were conducted at a scan rate of 1 mV/s from -0.4 V to 1.2 V vs. Ag/AgCl.
Results and Discussion
The results showed that the Cu and P microalloying in the welded joints had a significant improvement on the corrosion resistance of A588 Grade B weathering steel. The EIS measurements indicated that the welded joint with Cu and P microalloying had a higher charge transfer resistance (Rct) and lower double-layer capacitance (Cdl) compared to the base metal. This implied that the welded joint had a lower corrosion rate and faster corrosion inhibition.
The potentiodynamic polarization tests also supported the EIS results. The welded joint with Cu and P microalloying showed a higher corrosion potential (Ecor) and lower corrosion current density (icorr) compared to the base metal. This indicated that the welded joint had a better corrosion resistance and higher stability in the corrosive environment.
The improvement in the corrosion resistance of the welded joint with Cu and P microalloying can be attributed to the following factors:
1) The Cu and P microalloying increased the formation of protective oxide films on the surface of the welded joint. The Cu acts as a catalyst for the formation of Cu2O and CuO nanoparticles, which provide a physical barrier against corrosion. The P acts as a grain refiner, which promotes the formation of fine grains and uniform distribution of the oxide films.
2) The Cu and P microalloying reduced the formation of corrosion pits and cracks on the surface of the welded joint. The Cu and P act as a microstructural stabilizer, which prevents the formation of galvanic couples and intergranular corrosion.
3) The Cu and P microalloying enhanced the weldability and mechanical properties of the welded joint. The Cu acts as a deoxidizer, which reduces the formation of porosity and inclusion defects. The P acts as a strengthening element, which improves the tensile and yield strength of the welded joint.
Conclusion
In conclusion, this study showed that Cu and P microalloying had a significant influence on the corrosion resistance of A588 Grade B weathering steel plate welded joints. The welded joint with Cu and P microalloying exhibited higher corrosion resistance and stability in a corrosive environment compared to the base metal. The improvement in corrosion resistance was attributed to the increased formation of protective oxide films, reduced formation of corrosion pits and cracks, and enhanced weldability and mechanical properties. The results of this study provide insights into the design and development of weathering steel with improved corrosion resistance and performance in structural applications.
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