Effect Of Preheating Treatment On Oxidation Resistance Of Dilute Fe-Si Alloys

Because of its unique magnetic properties and mechanical properties,iron is used in various fields such as magnetic devices,electromagnetic products and military products,and has very broad application prospects.However,iron itself has the disadvantage of not being anti-oxidative,which leads to serious oxidation of iron products and causes great economic losses every year.With the fast improvement of modern industrial production,people have put forward higher and higher requirements for high temperature oxidation resistance of various industrial iron parts.Due to this,it is of much necessity to find new means of high temperature oxidation resistance of ferroalloys.So far,there are many methods to improve the oxidation resistance of iron-based alloys,such as painting,blueing and electroplating.However,these methods have disadvantages such as complicated process,easy detachment of the protective layer and even environmental pollution.At present,it had been reported in the literature that an Al₂O₃ or Si O₂ protective layer can be formed on the surface of copper by preheating the microalloyed Cu-Al or Cu-Si alloys to effectively improve its oxidation resistance.To date,there is still a lack of research on the improvement of iron oxidation resistance by preheating treatment.Therefore,this paper mainly studies the high temperature oxidation resistance and related mechanisms of microalloyed Fe-Si alloys under preheating conditions,in order to improve the working life of Fe alloys.In this paper,the effect of preheating treatment in H₂ atmosphere and different temperature conditions on the oxidation resistance of Fe-Six(x=0.5,1 or 2 wt.%)alloys was first studied.The results show that when the preheating temperature increases from 600? to 800?,the oxidation weight gain of the Fe-Si alloy after preheating treatment is obviously reduced,and the oxidation resistance is obviously enhanced.This is because with the increase of temperature,Si element diffused faster to the surface,forming a more complete Si O₂ protective layer.At 800? and 900?,the weight gain curves of preheated Fe-Si alloys almost coincide,meaning that there is almost no difference in oxidation resistance,and both have strong oxidation resistance,proving that a complete protective layer was already formed at 800?.In addition,when preheating at 800?,the surface of Fe-Si alloy with Si content of 2wt.%hardly oxidizes compared to other concentration samples,which proves that the integrity of Si O₂ protective layer of Fe-Si alloy also depends on Si concentration.This is because with the increase of Si element content,the greater the degree of Si element segregation to the surface during the preheating process,the easier it is to form a complete protective Si O₂layer on the metal surface,and thus the oxidation resistance of Fe-Si alloys is more powerful.In addition,in order to reduce the energy consumption during the preheating process,the effects of holding time and cooling rate on the oxidation resistance of Fe-Si alloys were further investigated.It was found that when the holding time of preheating treatment was shortened to 18 h,the oxidation degree of oxidized surface has little difference compared with holding for 24 h.This indicates that a relatively complete protective layer had been formed on the surface under the holding time,and it could play a good antioxidant effect on the matrix.For Fe-Si alloy under the condition of rapid cooling,the surface oxidation of alloy under the condition of low preheating temperature is more serious,and its oxidation resistance is poor.This is because in the process of rapid cooling,the protective layer is lack of self-healing ability to eliminate the defects or crack induced by the internal stress originated from the difference in thermal expansion coefficient between the substrate and the protective layer.When the temperature reaches 900?,however,the influence on the oxidation resistance of the Fe-Si alloy becomes weak.This is because,the temperature is higher,the element diffusion is more fully,and the continuity and compactness of the protective layer are better,which can eliminate the negative influence of internal stress caused by rapid cooling.