Microstructure Evolution And Action Mechanism Of Copper-rich Phase In Copper-bearing Ferritic Antibacterial Stainless Steel

The addition of a certain amount of copper to 430 ferritic stainless steel can provide excellent antibacterial properties while ensuring corrosion resistance,which will greatly expand the application range of 430 ferritic stainless steel.In this paper,the research on the microstructure evolution and action mechanism of copper-rich phase in copper-bearing ferritic antibacterial stainless steel was carried out.The effect of copper on hot workability was studied by hot compression test.The results show that with the increase of copper content,the deformation resistance of tested steel increases,the dynamic recrystallization process is hindered,and the heat activation energy increases.Moreover,when the columnar crystal is thermally compressed in different directions,the degree of dynamic recrystallization is different.Therefore,more attention should be paied to the deformation behavior of the triangular region to avoid hot working cracks.In addition,when heated at 1150℃,it was found that pure copper appeared in the oxide skin and at the interface between the oxide skin and matrix,indicating that copper spontaneously diffused to the surface from the slab inside and would be segregated and melted,which became a source of cracks for hot working.Copper also hindered the static recrystallization process of the tested steel and affected the recrystallization texture.But the matrix texture can be further adjusted by subsequent antimicrobial annealing.Antibacterial tests showed that the antibacterial rate of E.coli and S.aureus was 99.9%after annealing at 800℃ for 0.5 hour.With the increase of antibacterial annealing temperature and time,the copper-rich phase gradually developed into a rod shape.The Ostwald ripening process of the copper-rich phase at 800℃ was characterized.It was found that the copper-rich phase was mainly elongated in the rod direction and the ripening rate was 10.311 nm/s1/3.In order to overcome the limitation of studying crystallography orientation relation by TEM,XRD was used to systematically analyze the relationship between the macrotexture of copper-rich phase and the macrotexture of the matrix.on a 20 mm×25 mm surface in this paper.And the results showed that the rod-shaped copper-rich phase and the matrix have a K-S relationship,namely {111}cu//{110}Fe,<110>Cu//<111>Fe.Then the distribution of rod-shaped copper-rich phase was determined at millimeter,micron and nanometer levels by XRD,EBSD and TEM respectively,In the grain with {110} texture,the rod-shaped copper-rich phase is parallel to the surface,which has the largest exposed area and improves the antibacterial rate of the tested steel.In the new process of antibacterial annealing first and then cold rolling,it was found that cold rolling could cause deterioration of antibacterial properties.It was proved that the severe plastic deformation will cause the copper-rich phase to become smaller,and solidly dissolve into the matrix through the morphology observation of copper-rich phase,the distribution state of Cu elements and the change of matrix lattice constant.These were because a large number of dislocations occured during the cold rolling process,which significantly improved the gibbs free energy and provides driving force for the dissolution of copper-rich phase.In addition,the critical nucleation radius(rc)of copper-rich phase would be increased by severe plastic deformation.And the actual radius(r)of copper-rich phase will gradually decrease in the process of cold rolling.When the actual radius is less than the critical nucleation radius,the copper-rich phase would dissolve into the matrix.The process of "antibacterial annealing + low temperature aging"was developed in this paper.Thus the strength of the tested steel was also improved while ensuring the antibacterial rate.Since the antibacterial annealing temperature is high,the copper content in the matrix after the antibacterial annealing at room temperature is still supersaturated,so the strength of the tested steel can be improved by further aging annealing.After aging annealing,it was found that many nano-sized copper-rich phase particles were precipitated,and the hardness and yield strength tensile strength of the material were improved.The best aging process was annealing at 550℃ for 1 hour after antibacterial annealing at 800℃for 0.5 hour.Both yield strength and tensile strength can be enhanced about 160 MPa.Although the mechanical properties have been improved,the cupping value of the material has decreased,and the best cupping process is antibacterial annealing at 800℃ for 6 hours.It was found by electrochemical tests that the corrosion resistance of the tested steel increased with the increase of the solid solution copper content in the matrix,and gradually deteriorated with the growth of the copper-rich phase.During the immersion process,the surface of pure copper was found to be uniformly corroded,and the surface of the tested steel was pitting.The corrosion rate of copper after the formation of the primary battery was slowed down,and the corrosion rate of the tested steel was accelerated.The results showed that both copper-rich phase and matrix dissolved during the antibacterial process,which ensured that the tested steel had a lasting antibacterial function.