The effect of smelting processes on mechanical properties and microstructure of reduced activation ferritic steels was studied.Creep properties and impact toughness of reduced activation ferritic steels were obviously improved by vacuum induction melting followed by consumable electrode remelting process in comparison with the conventional vacuum induction melting process.The difference of impact toughness and creep properties between both steels mainly depended on the aspect ratio and mean size of precipitates.Decreasing the aspect ratio of carbides makes development of a shear band more difficult , which could increase impact energy and creep resistance.
KANG Wen-yiZHANG ChiFAN Nian-qingXIA Zhi-xinWANG Ping-huaiCHEN Ji-ming
A 304 stainless steel with the addition of 0.27 wt% Ag was found to exhibit excellent antibacterial properties. Based on Thermo-Calc calculation, a special heat treatment was introduced to obtain Ag precipitate in this steel. Anti- bacterial experiments show that the alloy can kill the adhering Escherichia coli effectively. Since the Ag element plays a key role in killing the adhered bacteria, microstructures of Ag and Ag-rich compounds were characterized by scanning electron microscopy and transmission electron microscopy. Ag-rich compounds with the size of a few microns were found to be embedded within the matrix and along grain boundaries, Moreover, pure Ag particles with a lattice parameter of 0.422 nm were found within the austenite matrix. The orientation relationship between the matrix and Ag particles was identified. Nano-sized Ag particles were precipitated during heat treatment, and the interfacial energy between Ag precipitates and matrix was determined by Becket＇s model calculation.
