| Copper-alloyed antibacterial ferritic stainless steel is one of the hot topics in the research of antibacterial metal materials due to its advantages such as simple preparation process,low production cost and human safety,whose advantages in the fields of medical equipment,household kitchen appliances,and folk structural materials are even more obvious.The low melting element tin is generally considered to be a harmful element in steel,however,its positive impact on the refinement of the microstructure,mechanical properties and corrosion resistance of stainless steel cannot be ignored.In addition,an in-depth understanding of the synergistic mechanism of tin and copper in antibacterial stainless steel has far-reaching implications for the development of a new alternative material.This article takes tin-and copper-alloyed 430L ferritic stainless steel as the research object,and systematically studies the microstructure and comprehensive properties of experimental materials under different heat treatment states,laying a foundation for the practical application of tin-and copper-alloyed ferrite antibacterial stainless steel.The main research results are as follows:Three furnaces of tin-and copper-alloyed antibacterial 430L ferritic stainless steel were melted using a vacuum induction furnace,and the elemental yield of the experimental steel is rather high,whose chemical composition meets the expected range.The typical inclusions in the 1#and 2#steel are mainly strip and round MnS-Al2O3 composite inclusions,while the 3#steel is mainly MnS-Al2O3 composite inclusions that adsorb certain tin and copper elements.Furthermore,the size of the inclusions in each steel is relatively small.The equilibrium phase diagram of 430L ferritic stainless steel with a copper content of 1.5%was calculated by Thermo-Calc thermodynamic software.It can be found that the aging treatment at 600?,700? and 800? is beneficial to the precipitation of copper-rich phase from the phase diagram.The theoretical composition of the copper-rich phase was almost composed of pure Cu(98.6%?99.7%),and contained only a small amount of other elements such as Fe,Cr and Mn.The hardness of 2#(430L-1.5%Cu)and 3#steel(430L-1.5%Cu-0.4%Sn)both increase and then decrease after aging treatment,and the hardness increase faster at high aging temperature,however,the peak hardness will decrease.In addition,it is found that tin has an effect of "accelerating" and "decreasing" the hardness change of copper-alloyed ferritic stainless steel;the grain size of 2#and 3#steel is slightly increased after aging treatment;due to the inhibition of dynamic recrystallization of tin element,the grain size of 3#steel is significantly smaller than that of 2#steel.EPMA and TEM were used to observe the micro-morphology of the copper-rich phase.It is found that the copper-rich phase in 2#and 3#steels would be significantly coarsened with prolonged aging time,increased from a few nanometers to several hundred nanometers,and the number decreased.Its coarsening behavior can be explained by the "Ostwald ripening" theory,and the strengthening mechanism of the copper-rich phase can be understood by the "Orowan bypass mechanism".When the solution-treated steel sample is used as a control group experiment,it is found that the antibacterial rate of 2#(430L-1.5 wt.%Cu)and 3#steel(430L-1.5 wt.%Cu-0.4 wt.%Sn)increased with the aging treatment time.Meanwhile,the antibacterial rate of 3#steel is higher than that of 2#steel:when the aging time is 79200 s,the antibacterial rates have reached 91.60%and 97.37%,respectively.The analysis of the surface passivation film found that the Cu element in the passivation film after aging treatment is more than the solid solution state is the main reason for its antibacterial improvement.Adding proper amounts of copper and tin elements to 430L stainless steel has a positive effect on its solid solution strength.After aging treatment,the strength and plasticity of 2#steel are slightly reduced,the tensile strength is reduced by about 30 MPa,and the elongation is reduced by about 9%(aging time is 79200 s).When the aging time is short(300 s),the tensile strength of 3#steel is increased by about 43 MPa,and the plasticity is reduced by about 3.6%.With the further extension of the aging time,it was found from the fracture morphology that 3#steel gradually changed from brittle fracture to plastic fracture.Appropriate amount of copper and tin elements can improve the pitting resistance of 430L stainless steel.After aging treatment of 2#and 3#steel,its pitting resistance will be reduced to a certain extent;when the aging time is longer,the pitting corrosion resistance of 2#and 3#steels has different degrees of pick-up. |
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