Corrosion Behavior Of Martensitic High-Strength Steel And Its Effect On Mechanical Properties

Martensite high strength steel has been widely used in aerospace,petrochemical and other fields because of its excellent mechanical and processing properties.But in order to obtain stable pure austenite region in high temperature zone,Cr and Ni content in martensitic high strength steel generally do not exceed 18%,which makes the corrosion resistance relatively poor.The heat treatment and welding of steel also have great influence on the structure and corrosion resistance of steel.Therefore,the aging time,coating antirust oil,aging time,antirust oil coating,and the aging time,coating rust oil,etc.were studied by metallographic observation,mechanical property test,chemical immersion test,polarization curve and impedance spectrum measurement,and X-ray phase analysis(XRD),transmission electron microscopy(SEM),X-ray energy spectrum analysis(EDS)The effect of welding on the corrosion behavior of martensite high strength steel matrix and its corrosion mechanism.The effect of Cl concentration on the corrosion process of martensitic high strength steel and the change of mechanical properties with corrosion degree are studied.The corrosion behavior of 00ni18co8mo5tial steel aged for 3,6h and 9h at 480?was studied by chemical immersion method,electrochemical impedance spectroscopy and extrapolation of Tafel polarization curve.It is found that the corrosion resistance of aging steel decreases with the increase of aging time.The results show that the corrosion mode of aging steel is pitting.The corrosion resistance of the samples with the best 3 hours aging was tested by chemical immersion,and the corrosion rate of the samples was calculated under the condition of oil coating and non oiling.It was found that the corrosion rate could be reduced obviously by applying anti rust oil.The corrosion rate of 00ni18co8mo5tial steel was faster in the early stage,and the corrosion rate tended to be flat after the soaking time reached 9h.Through the macroscopic observation of the corrosion samples,it is found that the corrosion type of the matrix and welding joint is typical pitting,and the structure is in the shape of river erosion.The micro morphology observation shows that small corrosion pits are formed in local area first when corrosion occurs.These small pits are connected with cl-until the surface falls off,and the corrosion pits further expand inward.The corrosion test on the welded joint shows that the pitting pits are mainly distributed in the weld area and the boundary between the weld and the heat affected zone.EDS analysis of corrosion pits and its surroundings shows that the content of Fe in the corrosion area decreases with the increasing corrosion degree.XRD analysis of corrosion products shows that the change process of corrosion products is Fe OOH?Fe(OH)₃?Fe₃O₄.The polarization curves and impedance spectra of the samples immersed in different Cl concentration solutions were tested.With the increase of Cl concentration,the capacitance arc diameter,impedance modulus value,polarization resistance and self-corrosion potential of the samples decreased continuously,the corrosion current density increased,the corrosion probability of aging steel increased,and the corrosion resistance became weaker.In addition,with the increase of chloride concentration,the donor density and acceptor density are increasing gradually,which indicates that the defects of passivation film increase and corrosion resistance decrease.With the development of corrosion process,the thick Ness loss rate of00ni18co8mo5tial steel increases,and the phenomenon of double peaks appears.It shows that there are two stages of corrosion:(1)the corrosion products are easily falling off on the surface,and chloride ions can easily penetrate the rust layer(2)The surface of the material produces dense corrosion products,which prevents the chlorine atoms from contacting the matrix.The equation of thickness loss rate and corrosion time is obtained by fitting:y=8.7171x^0.36(?),y=4.591x^0.524(b).According to power index B,the corrosion products produced by material corrosion have protective effect on the matrix,that is,the protective substances are generated in the second stage of corrosion.With the increase of corrosion time,the elastic modulus of martensite high strength steel has no significant change,but the elastic limit decreases;The yield point decreases with the increase of corrosion time,and the tensile strength and ultimate strain decrease.When the thick Ness loss rate reaches 62%,the maximum attenuation of fracture strain is 25%.