Study On The New Technology Of Hot-Dip Aluminizing Of Iron And Steel And Its Surface Coating Control Model

Hot-dip aluminizing is a technology that integrates with strengthening, protection and decoration on the surface of iron and steel. It can intensify a lot of properties of iron and steel in corrosion resistance, resistance to heat and oxidation resistance at high temperature, decrease the economic loss by corrosion and abrasion, prolong the life of ferrous products greatly and bring good benefits.Hot-dip aluminizing is a kind of method to form the transition layer and the surface layer. The paper deals with the technology of hot dip aluminizing in pure aluminum, containing rare-earth aluminum alloy bathes by water flux methods. On the conditions of laboratory, the new technology of no covering flux and the oxidation resistance at high temperature of iron are also studied. The composition and structure of hot-dip aluminizing samples are analyzed by using metallurgical microscope, SEM and XRD. In addition, the control models of the thickness of surface coating about samples of column and flat are investigated by fluid dynamics. The main conclusions are summarized as following:(1) The hot dip aluminizing samples of Q235 by the method of passivation containing 3% CrO₃ fluid and salt membrane method, which is mainly consisting of K₂ZrF₆ fluid posses excellent properties suitable for popularization and application, and receive the properties of JISH8642-95. (2) The rare-earth plays an important catalytic role in hot-dip aluminized. Rare earth obviously increase the corrosion resistance of hot-dipped layer, in which the 0.3%LPC rare-earth content is excellent, and the corrosion resistance is about 3 times as much as the pure aluminum. (3) The effects of aluminum bath temperature, immersion time and silicon content on hot dip aluminum for HT200 are studied. The results show that improving melt temperature and immersion time increases the thickness of aluminizing coat. Under the conditions of this experiment, the parameters which bath temperature is 740-810℃ and immersion time is 5¹0min are good chooses.Si restrains the growth of aluminizing coating. When Si% of melt is 2%, 6% and 9%, the thickness of aluminizing coat is 384μm, 200μm and 121μm respectively. The structure of aluminizing coat consists of top layer and intermediate diffusion layer (Fe₃Al majority), and is Fe₂Al₅ principally after diffusion annealing. After the aluminizing or aluminizing and annealing, their resistance to oxidation is over 2-8 times as much as that of non-aluminizing, the corrosion resistance was significantly improved. (4) The law of the thickness changing of surface can be simplified by the model of fluid dynamics in the procedure of hot-dip aluminizing.The investigation of the new technology on hot-dip aluminizing and the surface coating model provide the necessary information and theoretical basis. So the results of research posses have directing significance to industry application.