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 304 stainless steel containing 3.52 Cu (mass fraction %) and 430 stainless steel containing 1.47 Cu (mass fraction %) were studied with the aids of 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. The average grain size of both steel increases with increasing annealing temperature. The mechanism of Cu-rich phase precipitation in 430Cu at different annealing temperatures is: segregation of Cu atoms → Cu precipitation → congregation and growth → spherical ε-Cu → ellipsoidal → long rod. 304Cu Cu-rich phase precipitation mechanism: supersaturated solid solution → direct formation of FCC structure of Cu-rich phase → slow growth, and co-lattice with the matrix. In order to obtain a good match between strength and plasticity, the optimal annealing temperature range for 430Cu and 304Cu stainless steel is 800 °C∼900 °C.