Influence Of Rare Earth On Microstructure And Corrosion Resistance Of Maraging Stainless Steel

Maraging stainless steel was developed in the 1960 s,and it has been widely used in aerospace,machinery,nuclear energy and other fields.At present,the development direction of maraging stainless steel is to reduce inclusions and harmful elements in steel,and to develop low-cost maraging stainless steel with ultra-fine grain,uniform structure,ultra-high strength and good corrosion resistance.Appropriate addition of rare earths is in line with the development direction of maraging stainless steel.At present,the research on rare earths in maraging stainless steel is rarely reported.Therefore,this thesis will use rare earth additions to compare and study to clarify the isothermal aging process of rare earths on maraging stainless steel.Influence rule of microstructure and corrosion resistance.In this thesis,the 1# and 2# experimental steels are smelted in a vacuum induction furnace.After the isothermal aging process at 980℃ for 45 min and water cooling at500℃,the experimental steels were subjected to isothermally aged for 0min,60 min and180min by optical microscope,field emission scanning electron microscope,XRD diffractometer Vickers hardness tester and sample microstructure,precipitation,hardness,etc.were analyzed.At the same time,the periodic corrosion rate,polarization curve and AC impedance spectrum of the 1# and 2# experimental steels were measured isothermally aged for 0min,60 min and 180 min through the periodic infiltration experiment and the Princeton Verascan electrochemical workstation.Optical microscope and scanning electron microscope were used to observe the corrosion macro-microscopic morphology of corrosion for 3days and 7days and the change rule of rust layer within 7days of corrosion.The influence of rare earth on the corrosion of maraging stainless steel after isothermal aging at 0min,60 min and 180 min was analyzed.On this basis,the effects of rare earth on the microstructure and corrosion resistance of maraging stainless steel are summarized.The results show that compared with the 1# experimental steel without rare earth,the2# experimental steel is isothermally aged at 500℃ for 0min.The rare earth addition refines the matrix structure,inhibits the precipitation of chromium-rich carbides and precipitate particles,and makes the matrix structure in a chromium-depleted area.decrease,the distortion energy of the matrix decreases,the hardness value of the 2# experimental steel decreases,the cyclic corrosion rate decreases,the self-corrosion current density becomes smaller,the capacitive arc becomes larger,and the corrosion resistance is improved;after isothermal aging for 60 min,the precipitated phase particles begin to dissipate from the matrix.A large amount of precipitation makes the hardness value of the2# experimental steel rise significantly.The rare earth inhibits the network of chromiumrich carbides and the decomposition of the chromium-rich carbides,which leads to a decrease in the balance of chromium in the matrix,which reduces the cyclic corrosion rate of the 2# experimental steel.The corrosion current density increases and the capacitive arc becomes smaller,which reduces the corrosion resistance of the 2# experimental steel;isothermal aging for 180 min,rare earth inhibits the growth of the precipitate particles,which makes the precipitate particles in the matrix refine,and the fine particles strengthen the matrix.The hardness value of the 2# experimental steel keeps increasing slowly,and the structure is more uniform and denser,which reduces the periodic corrosion rate of the2# experimental steel,the self-corrosion current density becomes smaller,the capacitive arc becomes larger,and the corrosion resistance performance is improved.