High Temperature Oxidation Characteristics Of 590MPa High Strength Ship Plate Steel

In this paper,a 590 MPa high strength ship plate steel is designed.By means of microalloying,the steel is strengthened by adding Si,Mn and other elements in solution,and the low temperature toughness is improved by adding a large amount of Ni,the toughness was improved by adding Cr,Mo,Nb and other elements to refine the grain.The effect of temperature,time and atmosphere on the oxidation behavior of this steel was studied by means of thermogravimetric analyzer and rapid heating furnace.Scanning electron microscope（SEM）,energy dispersive spectrometer（EDS）,field emission electron probe microanalyzer（EPMA）and X-ray diffractometer（XRD）were used to observe and measure the microstructure,phase composition and element distribution of the oxide layer,and analyze the high-temperature oxidation behavior and mechanism,which provides a theoretical basis for the control of oxide sheet in actual production.The results show that the oxidation weight gain curve of 590 MPa ship plate steel conforms to the linear law when the temperature rise stage or the oxygen content is low.In the insulation stage or the oxygen content is high,in line with the parabola law.The oxide sheets from outside to inside are:the outer oxide surface layer,the outer oxide inner layer and transition layer.The outer oxide surface layer is mainly Fe-Cr oxides,and the outer oxide inner layer is mainly Fe-Cr,Fe-Ni and Fe-Si oxides.The transition layer mainly contains Si and Cr oxides.At the early stage of oxidation,Si O₂and Cr₂O₃island form first,and then Fe elements are oxidized and surrounds Si O₂and Cr₂O₃.As oxidation continues,Si O₂and Cr₂O₃form Fe-Si and Fe-Cr composite oxides with Fe,which eventually become the outer oxide surface layer.The Ni elements are enriched at the interface between the matrix and the iron sheet and form coarse particles.The Ni-rich particles prevent further oxidation.Finally,the Fe oxides and Ni-rich particles become the outer oxide inner layer.Internal oxidation results in the emergence of transition layer:O ion diffuses into the test steel and reacts with easily oxidized elements to form oxide particles;O ion diffuses rapidly through the grain boundary and forms a network intergranular oxide along the grain boundary.The transition layer which is closely bound to the matrix is more difficult to remove in production.