Influence Of Heat Treatment Process On The Structure And Corrosion Resistance Of 510L Hot-rolled Steel With Various Oxide Scales

In this paper, by using 510L hot-rolled steel as the basic compositions and oxide scales prepared on the surface of 510L steel, the effects of oxgyen concentration and heat treatment temperature on the oxide scales have been studied.Simultaneity,the influence of subsequent heat treatment temperature in primitive oxide scales on 510L hot-rolled steel also discussed here. By XRD,SEM,EDS etal, the phase composition and microstructure were analyzed and discussed.Finally, the corrosion resistance of steel with difference oxide scales were studied by using periodical immersion cyclic corrosion test, electrochemical polarization curve and inpedance test.The results were as follows: heat-treated at diferent oxygen concentration,the oxide scales consists chiefly of Fe₃O₄, some Fe₂O₃ and Fe,thickness of oxide scale and the Fe₂O₃ phase increased along with the increase of oxygen concentration, but oxygen concentration does not affect the survive of thickness of scale if the oxygen concentration was higher than 30%. If the oxygen concentration were used beyond the 10% concentration, they were shown to inhibit the growth of oxide scales, and too high oxygen concentration of chemical gas will cause increase remarkable. The results of corrosion test showed that the oxide scales have many defects produced belew high oxygen concentration and the oxide scale thickness was thin produced belew low oxygen concentration all were lead to the corrosion resistance of scales poor. The order of corrosion resistance of the scales under various oxygen contents from good to poor was as follows: 20%, 10%, 60%, 5%, 40%.Heat-treated at temperature between 500℃and 580℃,the oxide scales consists chiefly of Fe₃O₄ and Fe₂O₃.Thickness of oxide scale and the Fe₂O₃ increased along with the temperture ascension, and the oxidation behavior of steel follow the increment rule of the parabola as time increasement. The results of corrosion test showed that thickness of oxide scale might have a greater role in corrosion resistance, the order of corrosion resistance of the scale from good to poor was as follows: 580℃, 560℃, 550℃, 500℃.The primitive oxide scales on 510L steel consists chiefly of Fe₃O₄, some Fe₂O₃ and Fe. The amount of Fe₂O₃ is decreased from the margins to center across the width, the central area hardly containing Fe₂O₃. Fruthermore,there are quite many defect and Fe exists in the oxide scale. Subsequent heat treating has a certain influence on primitive oxide scales in the temperature range from 350℃to 550℃, especially subsequent heat treating at 550℃made the surface of oxide scale more continuous, the amount of pore and Fe present on the oxide scales were decreased. The results of corrosion test showed that the corrosion resistance of the scales increaced with the ascension of subsequent heat treatment temperature. The order of corrosion resistance of the scale from good to poor was as follows: 550℃, 500℃, 450℃, 400℃, 350℃, and the primitive oxide scale.