Studies On The New Technology Of CSP Process Of Medium And High Carbon Alloyed Steels

This paper makes a study of physical metallurgical mechanism and manufacture techniques of thin slab continuous casting and rolling process of medium and high carbon alloyed steels.As is well known, medium and high carbon alloyed steels are widely applied nowadays while its operating conditions are very harsh as followings. First, it demands high grinding, harden ability, wear resistance and ductility; Secondly, they can be applied only after hot rolling annealing or cold rolling; Thirdly, the hot-rolled alloyed steels should be of fine-shape and high-precision thickness; Last but not the least, the microstructure should have good isotropy, high cleanliness, ideal metallurgical microstructure and evenly distributed carbide shape. To meet all these high demands, some new production technologies must be applied on metallurgical,casting,thermo-mechanical process besides the optimal ratio of the steels chemical composition.When the carbon content is high, with the content of lactose higher than 0.45%, its segregation will increase shapely and the columnar grain crystal will grow sufficiently during the solidification processing. What's more, select crystallization will be severe, and the positive segregation of the centerline will intensify. At the same time, the bridging will hinder the supplement to the solidification end from the molten steel. Thus,.center porosity comes into being. Considering some technical characteristics that the slabs produced by CSP solidify quickly, the slabs come into being by liquid cooling and there is no repeated transformation from, thin slab continuous casting and continuous rolling (CSP) process is adopted. After the rational composition design, the totally new metallurgical control technique is used and hot-rolled steel plates of the medium and high carbon alloyed steels with low decarburized layer, good product homogeneity, high-performance, high additional-value and low cost are successfully developed.This paper did research on oscillating regulation of the components of the medium and high carbon alloyed steels with the carbon content (Wt%) from 0.3% to 1.0%, put forward the main factors which affected the oscillation and segregation and developed the access control to guarantee the composition uniformity and decrease the segregation during steelmaking, LF, and continuous casting and hot rolling process. The access control over the composition uniformity and segregation all has reached the international advanced level after the enforcement. The paper did research on morphology, quantity control and distributive characteristics of the inclusions such as Al2O3,SiO2,MnS and so on, which has much effects on the performance of the medium and high carbon alloyed steels. By The microscopic analysis, scanning electron microscopy analysis and electrolytic analysis, the author took inclusion morphology,quantity and distribution in different process conditions as well as furnace smelting process, and inclusion control of tundish into consideration, choosing the rational control process.By using thermal expansion and metallographic method, the author measured the thermal curve when the samples went through continuous cooling at different rate and drew the CCT curve of 30CrMo,50CrV4 and SKS51. Also the author determined the transformation temperatures of Austenite and its continuous cooling transformation curve. Through optical microscope and electron microscope, the author observed the samples'microstructure and analysed the effects on transformation temperature at different cooling rate. The author also analysed the effects on deformation parameters, Bainite transformation, pearlite transformation, CCT curve shape and location and the formation discipline of CCT curve under different processing. And at the same time, Austenite transformation process and the products microstructure and properties were researched during the continous cooling process, which laid a theoretical basis for establishing practical process systems.In order to control decarburization, the author did research on decarburization when the strip was hot-rolled during the thin slab casting and rolling process, compared the different decarburization between the thin slab casting and rolling process and traditional process and investigated the decarburization degree and influencing factors when the medium and high Carbon alloyed steels were hot-rolled under different processing condition.Controlled cooling processing (cooling rate and cooling temperature) and alloying element content are the main factors affecting the microstructure and properties. Continuous cooling transformation (CCT) is the theoretical basis on considering and determining the cooling technology. So according to the CCT of the characteristic steels, the author investigated how the coiling temperature and the key alloying elements affected the microstructure and properties.With the research on.high carbon alloy steel in the thin slab casting and rolling processing, Guangzhou Zhujiang Steel Co.,ltd. has produced high-quality continuous hot rolling plates for the medium and high carbon alloyed steels, with the quality up to the advanced level in the world, which not only upgrades our production technology on high-strength continuous hot rolling plates, but also changes the current situation that some industries such as construction machinery, advanced alloy tool manufacture and so on relies on import over a long period of time.