Effect of annealing temperature on the evolution of copper-rich phases in antimicrobial stainless steels

Abstract The effects of different annealing temperatures on the microstructures and properties of 430 stainless steel containing 3.52 Cu (mass fraction %) and 304 stainless steel containing 1.47 Cu (mass fraction %) were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) instruments, and the evolution mechanism of Cu-rich phase was explored. The results show that the microstructure of 430Cu stainless steel consists of polygonal ferrite, while 304Cu stainless steel consists of irregular austenite, and the average grain size of both increases with increasing annealing temperature. The precipitation mechanism of Cu-rich phase in 430Cu is that the Cu atoms are biased → Cu precipitation→ aggregation and growth → spherical ε-Cu → ellipsoidal → long rod-like transformation. The precipitation mechanism of copper-rich phase in 304Cu is that the supersaturated solid solution → direct formation of FCC structure of copper-rich phase → slow growth and complete co-location with the matrix. In order to obtain a good match between strength and plasticity of the test steel, the optimal annealing temperature range for 430Cu and 304Cu stainless steel is 800 ℃~900 ℃.