Effect of Boron on Microstructure and Corrosion Resistance of Decorative Stainless Steel

The microstructure and corrosion resistance of B-free and B-containing (mass fraction of 0.004%) stainless steels in solid solution state and aging state were studied by means of metallographic microscopy, scanning electron microscopy (SEM) and electrochemical workstation. The results showed that the microstructure of B-free and B-containing stainless steels in solid solution state was single austenite, and σ phase precipitated in stainless steel in aging state. The addition of B was helpful to improve the existence form of Mo-riched σ phase in the stainless steel. Compared with the B-free stainless steel, the B-containing stainless steel had a more positive corrosion potential, and the corrosion current density, pitting potential and corrosion rate of B-containing stainless steel were lower, which indicated that the B-containing stainless steel had better corrosion resistance. Compared with the B-free stainless steel under the same heat treatment conditions, the capacitive arc radius and phase angle of the B-containing stainless steel were larger, and the resistance of passivation film was smaller. As the aging time increased, the charge transfer resistance and passivation film resistance of the B-free stainless steel and the B-containing stainless steel gradually decreased, while the double layer capacitance and passivation film capacitance increased gradually. The pitting resistance of the B-containing stainless steel was better than that of the B-free stainless steel, which was mainly related to the improvement of the existence form of σ phase in stainless steel and the enhancement of density and stability of passivation film due to addition of B element.