Study On Corrosion And Wear Properties Of Ultra-high Chromium And High Carbon Dual Phase Steel

Duplex stainless steel has excellent strength,toughness,weldability and corrosion resistance of ferritic and austenitic stainless steel,which makes it widely used in the valve body,main coolant pipe and impeller of seawater circulating pump in nuclear power plant.But for the key parts of high performance manufacturing,the thrust bearing disk needs to bear the coupling damage of corrosion and wear during the start and stop stage of the nuclear main pump,and the wear resistance of duplex stainless steel can not meet the requirements.Some scholars have developed a super high chromium and high carbon duplex steel based on duplex stainless steel by alloying technology,but the research on it still remains in the aspects of casting technology,solidification process,solid solution structures and mechanical properties.In this paper,the chemical corrosion and electrochemical corrosion of 1.5%C-40%Cr ultra-high chromium and high carbon duplex steel obtained from metal mold and investment mold were studied by simulating the service environment of thrust bearing disk of nuclear main pump;The tribological characteristics of the system were investigated under dry friction and water lubrication conditions;The corrosion and wear properties of stellite12 alloy,which is commonly used in thrust bearing plates,are compared to evaluate the possibility of the alloy as an alternative material.The results show that:（1）The solution structure of ultra-high chromium and high carbon dual phase steel is composed of two phasesα、γand M₂₃C₆,the ratio is close to 1:1:1,and shows similar mechanical properties.The results of the immersion test in boric acid solution show that the annual corrosion rate increases with the temperature,but does not change with the soaking time.The average annual corrosion rate of metal mold and molten cast super high chromium high carbon duplex steel is close to that of the thrust bearing plate at 50℃respectively,which is 3.45μm/a and 3.58μm/a,both lower than stellite12 alloy,showed excellent chemical corrosion resistance.（2）The polarization curves of the ultra-high chromium and high carbon dual phase steel in boric acid solution are close,and the passivation phenomenon is obvious.The electrochemical corrosion parameters are better than stellite12 alloy.Especially,the self corrosion potential of uhcr high carbon duplex steel is positive,the current density of self-corrosion is the lowest,the corrosion tendency is the lowest,and the corrosion dynamic resistance is the largest.No passivation was found in the scanning range of anode polarization curve in 3.5%Na Cl solution.The self corrosion potential of ultra-high carbon duplex steel is positive,the current density of self-corrosion is the lowest and the chlorine resistance is the best;However,the corrosion surface of metal mould has different corrosion pits,which shows the worst resistance to chlorine.（3）Under the dry friction condition,the wear of particles,adhesion and fatigue wear occurs on the surface of super high chromium and high carbon duplex steel,and the wear volume is large and the wear resistance is poor.Under the condition of water lubrication,the friction coefficient and the specific wear rate of the alloy and PEEKCA30 are affected by load and speed,which are decreasing first and then increasing slowly;The smoother the original surface of polymer,the smaller the wear volume of the matched material,the longer the service life.The wear surface of the metal mold casting ultra-high chromium high carbon duplex steel has the bionic non smooth characteristics such as mesh pattern and pitting due to the falling off of hard carbide,which has the minimum friction coefficient and specific wear rate.The wear performance of the wear pair with PEEKCA30 shows excellent tribological characteristics.