Control Technology Of Inclusions In Steel Produced By35MN Forging Line

35MN Forgings, made by FuShun special steel corporation, has been extensively applied in the fields of automobile, petrochemical, iron and steel, electric power, shipbuilding, equipment manufacturing etc. The type, size, quantity and distribution rule of the inclusions directly affect the properties of the steel, such as strength, elongation, toughness, machining ability, corrosion resistant ability, surface roughness and welding ability. Therefore, in this article, the author mainly studied the inclusions during melting process, exploring the origin, forming mechanism, and revolving rules of the inclusions and providing control measures on process inclusions, in order to obtaining high quality product.As for the aspect of the inclusion researching and controlling, the inclusions could be located employing the method of Ultrasonic Testing(UT), besides, the inclusions could be classified and qualitative analyzed employing metallurgical microscope and scanning electron microscope etc., to finally determine the origin of the inclusions. And in addition with the method of computer simulation, field process test and data statistics, the conclusions could be decreased adequately.The conclusions could be obtained as follows:Firstly, the deoxidization method and the aluminum content in product analysis affect inclusions in a large way. Secondly, choosing adequate casting powders and runner bricks could reduce the content of foreign inclusions in casting molded ingots obviously. Thirdly, increasing casting temperature and casting rate tend to enlarge the liquid phase area and to improve the liquid flow at the bottom part of ingots. After casting, extending the time of removing the car holding the cast panels properly could create a channel for the floating upward of inclusions. Optimizing the parameters for shielding gas of Argon, and taking reasonable argon protective process could effectively reduce the inclusions resulting from the second oxidation of liquid metal during casting. Enlarging the dimension for upper mouth of the upgate could lower the spraying height of liquid metal in mold. Extending the length for horizontal tundish could reduce the impact force generated from the entrance of the molten steel. Modifying the shapes of spider bricks, by reference to the design principle of the turbulent current controllers for continuous casting process, could improve the flow field, and reduce the probability of inclusions originating from slag involving during casting. Changing the shape of mold bottom from semi globular to conic (rhombic taper), and chamfering the inner casting mouth could improve the fluidity of the molten steel and reduce the occurrence of the bow wave at the two sides. Meanwhile, augmenting the taper of casting mold could finally increase the rate of floating upward for inclusions. Lastly, Taking reasonable hot topping technique, using high-quality insulated plates, good exothermic powders and a certain amount of insulating agents, meanwhile, controlling the assemble quality of insulated plates, the addition time and addition way for exothermic powders, which could control the liquid surface and reduce the precipitation of the iron grains at the unit time, so as to create good conditions for the ascending of inclusions during the initial solidification stage, and to reduce the content of inclusions at the bottom part of ingots.By taking the aforesaid measures, the inclusion issue for large sized steels has been solved essentially, and has achieved good results. In2009, the whole year’s nonqualified rate for inclusions inspected by the way of non destructive testing (NDT) dropped from14.6%to2.5%, falling by83%compared with the previous year.