Effect of Metal Surface Treatment Agents on the Mechanical Properties and Corrosion Behavior of 2205 Duplex Stainless Steel by PAW

Plasma arc welding (PAW) technology is a new protection method for the welding process of 2205 duplex stainless steel, in which new protection devices are added outside the welding process, and self-formulated metal surface treatment agents are used to protect the PAW joints of 2205 duplex stainless steel. The work aims to improve the mechanical properties and corrosion resistance of 2205 duplex stainless steel. With the metal surface treatment agent as the medium, the protection experiment was conducted on the 2205 duplex stainless steel PAW joint and the effect of metal surface treatment agent on the mechanical properties and corrosion resistance of the welded joint was studied. Scanning electron microscopy, energy spectrum analysis, Vickers hardness tester, universal testing machine, and electrochemical workstation were used to analyze the properties of original sample, protected sample without metal surface treatment agent and protected sample with metal surface treatment agent of 2205 duplex stainless steel during PAW. The experimental results of the three samples were compared. The comprehensive results analysis showed that 2205 duplex stainless steel was protected by a metal surface treatment agent. The elements in the metal surface treatment agent diffused into the material, forming a protective layer with a diffusion depth of no less than 0.005 mm. The Vickers hardness tester analysis showed that the weld hardness was 262HV-271HV, an increase of 25%, and the hardness in heat affected zone was 262HV-271HV, an increase of 15%. The tensile test analysis of the universal testing machine showed that the tensile strength of the duplex stainless steel welded joint increased by 20%, effectively improving the mechanical properties of the 2205 duplex stainless steel PAW joint. By electrochemical workstation experiments, a comprehensive analysis was conducted on the dynamic potential and AC impedance of the original 2205 duplex stainless steel sample, the sample without metal surface treatment agent, and the sample with metal surface treatment agent. The analysis showed that the polarization curves of the three samples had obvious passivation regions, and the passivation regions were relatively wide. Electrochemical tests showed that the pitting potential and the maximum difference between pitting potential and self-corrosion potential in the polarization curve of PAW with metal surface treatment agent protection for 2205 duplex stainless steel were 0.287 6 V and 0.555 4 V, respectively. The passive current density was the smallest, and the capacitance arc radius of the metal surface treatment agent PAW sample was the largest in AC impedance analysis. The maximum resistance of the inner layer of the passive film was 7.531×105 Ω·cm2. The corrosion resistance of the surface metal surface treatment agent PAW sample in the electrochemical test was the best. The main mechanism of PAW metal surface treatment agent protection welding for 2205 duplex stainless steel was that the electronegative atoms such as N, S, P, O in the metal surface treatment agent adsorbed onto the metal surface along with C and H atoms, changing the double layer structure beneath the coated metal surface and increasing the activation energy of metal ionization. As a result, during the transformation of ferrite to austenite, the austenite that could not be precipitated in the weld seam during cooling continued to precipitate, causing the fine or blocky distribution of austenite on the ferrite, while C3H9NO acted as a surfactant to promote intermolecular bonding. During the welding process, the transformation between phases of 2205 duplex stainless steel was not completed, and the melt pool was not fully crystallized. Surfactants could promote the reaction of other chemical components of the metal surface treatment agent with 2205 duplex stainless steel, compensating for the chemical elements in the surface treatment agent into the weld seam. The final conclusion indicates that the mechanical properties and corrosion resistance of the 2205 duplex stainless steel PAW joint protected by the metal surface treatment agent are optimal. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.