Study On High Temperature Oxidation And Descaling Of Fe-Si Alloy Steel

Fe-Si alloy steel is a kind low-carbon-content alloy steel,and it was an indispensable material for its soft magnetic property used in electronics,electric power,machinery,and military industries.The quality and capacity of Fe-Si alloy steel is often used as an important indicator to measure the level of special steel manufacture of a country.During hot rolling,an oxide scale is formed on the surface of the strip.The addition of Si element improves the electromagnetic performance of the strip,but at the same time produces a more complex oxide scale.Compared with unalloyed steels,Fe-Si alloy steel has more serious oxidation loss in reheating furnace,and the scales are more easily to cause scale pressing defect and lack of pickling.For some strips with serious scale pressing defect,steel pits occurs after acid pickling,and the pits will be kept in the cold-rolled process,which would even affect the electromagnetic performance and lamination capability of the final product.In this study,Fe-Si alloy steel with Si content of 0.5%to 3.1%wt was investigated by experimental analysis methods such as TGA,SEM,EDS,Raman,XRD,and electrochemical pickling simulation,as well as elastic-plastic mechanics and curvature integration method.The study includes the high temperature oxidation behavior,the descaling behavior,the acid pickling behavior,and the effect of tension leveling on the acid pickling behavior of the Fe-Si alloy steel.The main contents and results are as follows:(1)Thermogravimetric analysis and metallographic observation were employed to investigate the effects of temperature on the oxidation behavior of Fe-0.5Si alloy steel.The oxidation kinetic curves of Fe-0.5Si alloy steel in the air of 1000?1200 ? followed a parabolic-linear law.The parabolic rate constant,the linear rate constant and the duration of the parabolic stage increased with the increase of the oxidation temperature.Due to the physical state transformation of Fe2SiO4-FeO in the internal oxidation zone at different temperatures,the iron ions had different migration rates at different oxidation temperatures,which makes the continuous time of parabolic stage and the oxidate rate of linear stage varied with temperature.Below 1177 ?,the solid solution of Fe2SiO4 inhibited the migration of iron ions,leading to higher oxidation resistance of Fe-Si alloy steel.Above 1177 ?,Fe2SiO4-FeO eutectic alloy promoted the iron ion migration,and Si element became the main factor to intensify oxidation loss.(2)To solve the problem of the frequent presence of the initial scale pressing defect after heating at 1150 ? in a high-Si steel in industry,a high temperature oxidation experiment of Fe-Si alloy steel with different Si content was designed.The Si content had a great in fluence on the descaling of Fe-Si alloy steel during high temperature oxidation.The high-Si steel was in an outward oxidation state when the oxidation temperature was 1200?,while the high-Si steel was in an inward oxidation state when the oxidation temperature was 1150?.The inward oxidation state deteriorated the descaling performance of the initial scale.In order to reduce the scale pressing defect and the oxidation loss in the hot rolling process,an optimization method of the heating process according to Si content was proposed.The optimization method can provide a technical reference to improve the slab reheating technology of Fe-Si alloy steel.(3)In order to solve the problem of scale residue on the surface of Fe-Si alloy steel after acid pickling,an electrochemical simulated pickling experiment of Fe-Si alloy steel with different Si contents was designed.The pickling process of Si-free steel and low-Si steel can be divided into three stages:the gestating period,the accelerating period and the stationary period.However,the high-Si steel exhibited only two stages:the accelerating period and the stationary period.Pickling in HC1 solution,H2SiO3 was generated and would adhere to the surface of strip at the end of acid pickling,leading to the imcompletion of acid pickling and the formation of scale residue defect.Adding HF acid in the HCl solution was found to eliminate the scale residue defect,which offered a new solution in improving pickling process of Fe-Si alloy steel.(4)As for acid pickling,the effect of tension leveling on descaling rate was investigated.An electrochemical pickling experiment was employed to build a prediction model for the pickling time shortening rate.Using pickling time shortening rate as an indicator,the pickling efficiency was assessed with different curvatures and elongations.The saturation points of curvature and elongation during the process of pickling were calculated.Based on elastic-plastic mechanics and curvature integration,an optimization model for tension leveling process was constructed,with curvature and elongation as parameters to be optimized.The model produced a tension-bending moment regulatory range,which provides a theoretical guidance for parameters optimization of a tension leveling.