Research On High Temperature Oxidation Behavior Of Several Stainless Steels

Using the method of constant temperature oxidation weight researched hightemperature oxidation behavior of316LN and429stainless steel in the airunder700℃,800℃,800℃. The surface cracks on316LN austenitic stainlesssteel plate after rolling in a factory, influence the using performance and surfacequality of steel sheet. The purpose of this paper is to study the formationmechanism of surface crack. The reasons for the formation of surface crackswere initially determined through the surface morphological observation,metallurgical structure observation, sample cross section scanning and energyspectrum analysis. Then using ANSYSLS-DYNA finite element simulationsoftware for the rolled piece with surface bumps, simulated the rolling processand identify the reasons for crack formation. Through the analysis of thephysical and chemical testing and numerical simulation of the plate rollingprocess knew that the formation of surface crack was caused by oxide. Inaddition,304stainless steel crucibles used in the production of high temperaturegraphite after several cycles, under the condition of natural gas and air mixtureheating, appeared severe oxidation failure phenomenon. Upper cruciblescorrosion was serious layering and fell off, lead to the crucibles can’t continue to use. In order to reduce the economic benefit, analyze the causes of thisphenomenon. The experimental results were as follows:(1)316LN stainless steel was antioxidant under900℃,800℃, oxidefilm appeared cracks and fell off. It was completely antioxidant under700℃with excellent oxidation resistance.429stainless steel were completelyantioxidant level under900℃and800℃. By comparison, it can be seen thatthe antioxidant capacity of316LN stainless steel not as good as the antioxidantcapacity of429stainless steel under900℃and800℃.(2) For316LN stainless steel, oxidation product was Cr2O3, MnCr2O4,FeCr2O4and Fe2O3under900℃. The oxide film surface was mainly Cr2O3,NiCr2O4, FeCr2O4and small amounts of Fe2O3Under800℃. The compositionof oxide film was mainly Cr2O3, a small amount of NiCr2O4, FeCr2O4and Fe2O3700℃. For429stainless steel, oxide film cannot fully cover the surface of thespecimen. The oxidation product was Cr2O3and FeCr2O4under900℃;oxidation product was Cr2O3under800℃.(3) Oxidation kinetics curve of316LN stainless steel accorded with thegrowth law of parabola to a straight line, a straight line to parabolic. Oxidationkinetics curves of429stainless steel conform to the parabolic growth law.(4) The oxidation rate of316LN and429stainless steel increased with theincrease of oxidation temperature. Before35h, the oxidation rate of429stainlesssteel was more than the oxidation rate of316LN stainless steel under900℃.Asthe extension of oxidation time, oxidation rate of429stainless steel was gradually less than the oxidation rate of316LN stainless steel. The oxidationrate of429stainless steel was always less than the oxidation rate of316LNstainless steel under800℃.(5) Plate surface cracks in316LN presented "the minute". The head ofcracks was consistent with the rolling direction. There was no obvious regularitycrack s distribution.the surface of the bumps were residual with Fe, Cr and othercomposite oxide, because of the incomplete surface descaling. In the rollingprocess, the bumps were rolled and turned into the substrate under the affectionof the friction between rolls and slab. Then the oxide on the surface of the slabfell off, while the other part was embedded into the matrix. And due to the lowcombination with the matrix, high hardness and brittleness, the oxide cannot bewelded in the further rolling process. As a result, the cracks formatted on thesurface of the matrix.(6) The effective ways to improve the quality of316LN steel plate wasproperly increasing the intensity of descaling. Implement the grinding treatmenton the slab surface when necessary.(7) Finite element simulation software ANSYS/ls-dyna can visuallysimulate the plate rolling process, observe stress and strain field, displacement,velocity of different time and the displacement change rule of a point with thetime in the process of rolling. It can effectively solve the problems in the processof rolling.(8) The surface of304stainless steel crucible appeared severe oxidation failure phenomenon. The formation process of oxide was that Cr element spreadto the surface of the metal substrate and reacted with oxygen to form Cr2O3. Themass Ni, Fe elements, which transfer to the surface, also reacted with oxygen toform the Ni, Fe oxide. Then Cr2O3generated volatile CrO3which lead to volatileof part Cr2O3and damage of Cr2O3membrane layer.(9) For304stainless steel crucible, the thickness of oxide layer on theupper was about200microns. The outer oxide was Cr2O3and Fe3O4, and theinner oxide was NiO and Cr, Fe oxides. The thickness of central oxide layer wasabout100microns. The central oxide layer was the Cr, Ni, Fe oxides.(10) By changing austenitic stainless steel crucible to ferrite stainless steelcrucible can extend the service life of crucible and improve the economicbenefit.