Study On Solidification Process And Microstructure And Properties Of Ultra High Chromium And High Carbon Duplex Steel

Duplex stainless steel has excellent toughness,weldability of austenitic stainless steel and high strength,chloride stress corrosion resistance of ferritic stainless steel.It has been widely used in petroleum,natural gas,fertilizer,paper making and food equipment industries.However,with the rapid development of modern industry,the requirement of material properties is increasingly stringent,and the existing duplex stainless steel can not meet the needs of industry.Especially in the harsh service environment of mineral processing,papermaking,desalination and nuclear power,it is urgent for materials with excellent corrosion resistance and abrasion resistance to undertake high-performance manufacturing of key components.A new type of 1.5%C-40%Cr ultra high chromium high carbon duplex steel was studied in this paper.The solidification structure,solution structure,mechanical properties and wear and corrosion resistance of 0.46%Si and 1.36%Si investment casting duplex steel were compared and analyzed.The influence mechanism of Si content on the solidification path of Fe-Cr-C alloys is discussed.The solidification structure,solution structure and properties of ultra high chromium and high carbon duplex steel?containing 0.46%Si?in investment casting and metal casting were compared and analyzed.The effects of solidification rate on the solidification path and the stability of solidification structure were discussed.By changing the cooling rate of solution treatment?air cooling and oil cooling?,the solution treatment structure and properties of 0.46%Si investment casting duplex steel were studied in detail.The experimental results show that:?1?The content of Si influences solidification process and microstructure of ultra high chromium and high carbon duplex steel.The phase compositions of 0.46%and 1.36%Si Cast duplex steels are?,?and M₂₃C₆,but the solidification process is different.When the content of Si is 0.46%,?ferrite dendrites,dendritic(?+M₂₃C₆)eutectic structure,peritectic?austenite around?ferrite dendrites,and chrysanthemum-like(?+M₂₃C₆)eutectic structure were formed in turn.?ferrite is converted to??₂+??eutectoid in subsequent cooling.When the content of Si increases to 1.36%,there is no chrysanthemum-like eutectic formation(?+M₂₃C₆),and the peritectic process of?is incomplete.The increase of Si content enlarges the?phase region,decreases the?phase region and prolongs the L?(?+M₂₃C₆)eutectic process until the end of solidification.There is no L?(?+M₂₃C₆)eutectic process.The structures of the two steels are composed of?,?and M₂₃C₆ after solution treatment.The content of ferrite in high silicon duplex steel increases obviously and is continuous with each other.Its mechanical properties are higher,but its wear resistance and corrosion resistance are slightly reduced.?2?The solidification rate also has an obvious effect on the solidification process,structure and properties of ultra high chromium and high carbon duplex steel at 0.46Si.When investment casting is used,?ferrite dendrites,dendritic(?+M₂₃C₆)eutectic structure,peritectic?austenite around?ferrite dendrites,and chrysanthemum-like(?+M₂₃C₆)eutectic structure were formed successively.And?ferrite is converted to??₂+??eutectoid in subsequent cooling.When metal mold casting with higher solidification speed is adopted,there was not enough time for the eutectic process of L?(?+M₂₃C₆)to proceed.(?+M₂₃C₆)eutectic is rare,and the main eutectic is reticulate(?+M₂₃C₆),and ferrite does not decompose.The structures of the two steels are composed of?,?and M₂₃C₆ after solution treatment.The carbides in dendritic and chrysanthemum eutectic in investment casting duplex steel are cracked and spheroidized.However,the reticulated carbides in the metal mold are relatively stable and can be retained after solution treatment.Compared with investment casting duplex steel,it has higher hardness,but its tensile strength,fracture toughness and wear resistance and corrosion resistance are slightly reduced.?3?The cooling rate of solution treatment affects the structure and properties of investment casting duplex phase steel at 0.46%Si.It is found that when the cooling rate increases from air cooling to oil cooling,the structure retains a small amount of chrysanthemum carbides.But the mechanical properties and wear resistance and corrosion resistance will be slightly reduced.