The main reason for the impact bearing steel surface oxidation iron

1 the influence of finishing temperature and speed of iron oxidation process is Fe - — FeO— — Fe3O4— — As temperatures rise, Fe2O3, oxidation rate also gradually increased. In the 600 - Temperature range of 800 degrees, the oxidation of iron is able to block the spread of iron and oxygen atoms, so instead, oxidation rate no longer continue to increase. When the temperature over 800 degrees, the tin oxide hinder the diffusion of power will reduce, thus oxidation speed increases quickly again. Due to the growing temperature, oxidation rate is accelerated, therefore in unit time, with the thickness of the bearing steel surface oxidation iron oxide temperature grow taller and thicker. Similarly, high speed can reduce the bearing steel exposed to air in the high temperature time, thus reducing the thickness of the tin oxide. Therefore, in order to reduce the thickness of the tin oxide, the temperature of the hot rolling bearing steel should be as low as possible and as high as possible under the speed of rolling. Look from the structure of the iron oxide, finishing temperature - in 700 Between 900 degrees, the formation of iron oxide containing 80% FeO, 10% to 90% 20% of the Fe4O4. In temperature greater than 900 degrees, oxide or oxide gas is large, the iron will quickly be oxidation, Fe2O3 can rapid forming at high temperature, the oxidized iron except Fe3O4 FeO will not appear, and began to form in the metal surface of Fe3O4 Fe2O3 surface covered with a layer of thin. Improve the rolling speed can reduce the thickness of the tin oxide, however, too high speed will make coiling temperature increase rapidly, and cause the rich iron oxide austenite transformed into Fe3O4, after to clear the oxide on the surface of bearing steel sheet ( Pickling) Work difficult. Therefore, accurately control speed is in favor of the important factors of pickling. The research results show that have the best pickling time tin oxide, finishing temperature should be 850 degrees. 2 we know that the influence of cooling rate, general hot rolling bearing steel surface oxidation iron has three layers, close to the lining of the base iron for rich austenite, middle of Fe3O4, outer layer of Fe2O3. Which is advantageous to the pickling rich austenite in over 575 degrees is stable, below 570 degrees when rich FeO in the austenite is not stable, and according to the four FeO = = = = = Fe3O4 + Fe. When the temperature further reduced to 300 degrees, the shift will be close to zero. If the iron oxide layer - in 570 Rapid cooling between 300 degrees, then, rich layer's will not break down and be fixed at lower temperatures, and pickling rich austenite structure is obtained. Slow cooling, the metal layer's with slow cooling in gradually reduce, therefore, bearing steel in the cooling area cooling speed is slower, tin layer zhongfu's only a small amount of existence or not at all. Is generally on the output roller spray high-pressure water to speed up the cooling speed of bearing steel. In the case of water, the thickness of the tin oxide increases very fast. Because iron oxide in water than in air to form fast, therefore, the long stays in the water vapor in the atmosphere, the formation of iron oxide is, the more the FeO content is less, so accurately adjust the cooling speed of water jet section and as much as possible to reduce the residence time in the water is very necessary. 3 the influence of the coiling temperature of bearing steel coiling temperature - in 600 700 degrees, the tin layer thickness increases and have no obvious impacts. However, the higher the coiling temperature, at the edge of the bearing steel head and tail will generate Fe2O3, these are what we don't want to. Further reduce the coiling temperature on the thickness of the iron oxide the no effect, but bearing steel edge and the tail risk of Fe2O3 reduced, at the same time, the rich from the transformation of austenite to Fe3O4 degree is reduced. When the coiling temperature from 700 degrees to 600 degrees, pickling time can be reduced 10% 15%. In order to control the rich austenite transformation, bearing steel should be at relatively low temperatures, such as 500 - 550 degrees of volume, but this will result in bearing steel cooling time before coiling increased, leading to the increase of iron oxide thickness nonuniformity, Fe3O4 will grow in quantity, rich austenite decreases, therefore, must to find out the best bearing steel mill coiling temperature, in order to reduce the bearing steel rich after cooling austenite transformation, prevent the tin thickness increased significantly. The experimental results show that in 550 - 590 degrees when coiling, bearing steel iron oxide layer on the thin, the layer's thicker, rich austenite decomposition least, thus can reduce the pickling time. 4 the influence of other factors in order to avoid the rich austenite transformation, must quicken the cooling speed of plate roll, especially in the 350 - 500 degrees within the scope of the cooling speed to achieve very high level. In recent years, all the new production of steel rolling - mill roll weight is greatly increased, then the plate roll cooling time. - for example, volume weight of 4 Increased to 20-6 t 25 t, cooldown by 1. 5 - 2 t extended to 3 day and night. 5 - 5 day and night. This rich austenite turn completely, bring difficulties to pickling work. In order to improving the structure of sheet metal at present some countries put the plate roll into the water in the container, make the temperature of the plate roll down to less than 350 degrees. Facts have proven that this is good for improving pickling speed. The only shortcoming of this approach is that steel volumes, peripheral cooling abruptly, and the central cooling slowly, will cause metal structure is not uniform. In pickling trials, worthy of note is the influence of roll roughness. In the use of coarse damaged roll, often on the edge of the bearing steel can cause pickling time extended by about 50%. To sum up, with greater speed, smooth roll and low finishing temperature and coiling temperature, and high cooling speed, can be beneficial influence on hot rolling bearing steel pickling.