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How To Realize High Strength Of Alloying Hot-dip Galvanized Steel Sheet Jul 10, 2017

              In order to adapt to the lightweight of car body and improve the safety performance of anti-collision, the trend of the automobile industry to adopt more than 590MPa high strength steel plate is rapidly increasing. According to the requirement of rust prevention and corrosion protection to improve the service life, the alloying hot-dip galvanized steel Plate (GA) is still the first choice under the current technical conditions. In order to increase the tensile strength of these plates, elements such as Si and MN have been added to the steel. However, these elements are easily oxidized, in the hot Dip Galvanized steel plate annealing process, will be preferentially oxidized and easily cause uneven local oxidation, on the surface of the steel plate to form SiO2 and Mn2sio4 oxides, which affect the adhesion between the surface of the steel plate and galvanized layer, resulting in a problem of plating. In addition, p, which is also added as a solid solution strengthening element, tends to exist in the grain boundary or on the surface of the steel plate, thus affecting the alloying reaction in the process of hot dip galvanizing of steel plate.Galvanized Steel Sheet

              As a solution, a variety of pre electroplating methods and the control of air composition in annealing furnace oxidation reduction method, but the economic and effect of these methods are not necessarily consistent, so it is necessary to the steel plate composition design, electroplating technology and equipment to do further research and development. To avoid the adverse effects of the added elements above, you must minimize the amount of these elements or add other harmless elements to the requirement of strength. Therefore, the steel plate with good adhesion and proper alloying reaction speed has become the focus of development. In the early 90, a 440MMPa high strength GA steel plate was developed to ensure the adhesion of the coating by adding a solid solution element such as MN, but the appearance of the steel plate was not suitable for the car panel. In order to solve this problem, the strength of the steel plate can be reduced by other means, such as grain refinement and precipitation enhancement, to reduce the added amount of Si, MN and P, and to develop 440MPa high strength GA steel plate. For example, by adding NB, which is equivalent to 3 times times that of if steel, by dispersing the micro-niobium-carbon compound, it is possible to develop a steel plate with high strength and good adhesion. In the application of structural parts, the use of oxide to generate free energy can be relatively high, even in the annealing process does not occur in the local oxidation of MO elements, reduce the addition of SI, MN, the development of dual-phase 550MPa with good coating adhesion of GA high-strength steel. Also, take trip steel as the substrate, add to the adhesion of the coating to the small impact of the AL element to replace the previously added Si, but also developed high strength GA plate.

               In the process design, the use of 800 ℃ above the high-temperature reduction heating, can eliminate the micro-leakage plating, and improve the coating wettability of steel containing easily oxidized elements. In addition, the surface modification methods, such as NI, Fe, Fe-o, fe-b, etc., or by adding the internal oxides such as B to reduce surface enrichment, have obvious effect.Galvanized Steel Sheet

               While improving the strength of steel plate, it is necessary to take into account the weldability. To this end, the composition of the steel plate must be reduced to the weldability of carbon and other strengthening elements (such as to improve the hardenability of C, Si, MN and other elements can lead to the deterioration of spot welding). The solution is to add Ti, NB, MO and other carbon nitride elements to produce high strength GA steel plates with excellent spot welding quality.Galvanized Steel Sheet