| With the advancing steps of China entering the World Trade Organization, the global economic trend makes that the competition between iron & steel enterprises home and abroad becomes more and more violently . The iron & steel enterprises at home are facing the challenge from abroad, of the import products which is produced in high quality and with low cost. In order to exist, the demand on product quality is getting higher and higher. Many factories begin to innovate the present equipments and produce procedure ,in order to improve the inner & outer quality of billets. In such situation, we are asked to cooperate with the technical department in Shandong LaiWu Steelmaking Factory( LWSF) on the study of the improving of billet inner quality problems and the optimizing of secondary cooling zones.In this article ,according to the fact of produce spot in LWSF, it theoretically analyzes the engendering mechanism of central loosening and segregation in billets, concerning affecting factors and concasting techniques. In practice, we study the producing Grade 45# steel on No.3 continuous casting machine ,on one hand, and apply two dimension heat transfer mathematical model to simulating the cooling temperature field of 150X 150mm2 billet. All this founds the basis for dynamic distributing of cooling water in secondary zones. On the other hand, after having some check-up of the cooling water volume, we improve the quality of cooling water , adjust the spraying devices and water volume in secondary cooling zones. In the mean time, we take some samples of the billets to have macrophotographical examination, and the concerning analysis results come to the following primary conclusions:1. In the thesis, the simulation result of the surface temperature before straightening, approximately explains the fact within the permitting error range, but the model is very coarse, generally speaking. Because of the limited condition and insufficient capitals, we can only measure the superficial billet temperature before the straightening machine. In order to make the model more fit for the billet production, we should firstly set more temperature detecting point in the secondary cooling zones to get plenty of data of surface temperature, and then use the linearr regression method to figure out the coefficient in the equation of drawing speed and water volume in different section of the secondary zones, and make use of parameter controlling method to control the distribution of secondary cooling water. The work done in this article, contributes to the latter research of dynamic distribution of secondary cooling water.2.1n the macrophotographical test of billet, the analysis results probably explain the condition of the equipments ,it has a certain role in conducting practical production. Because the operation of getting billet samples disturbs the fluency of operating process ,the amount of samples is limited. Although we have get same effect in the research, to get more advancement ,we should do further and systematic work inequipments, procedure and sample examinations.3. Considering of not decreasing the fluidity of steel in production, we can apply low superheat technique to cast steel under protection. This helps to reduce the column crystal area, enlarge the ,that to say, it improves the inner billet quality. LWSF have done a good job at this aspect in the procedure, thus their efforts get a better return.4. After adapting electric magnetic stirring( EMS) in the mould, it helps the inclusions to float in the mould ,and improves the cleanness of casting steel; what is more, EMS also contributes to the uniform forming of nucleus in the mould and does good to the improvement of inner& outer quality. All these can be proved in practice.5. Because the phenomena of water leakage in cooling water circuit system, the factual water volume inspected is far less than the designed water volume. For this kind of reason , it has some disadvantageous effect on the billet quality, and it leads to the leakage easily. After...
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