Research On Improving Q690D Heavy Plate’s Yield Rate

The yield rate is a crucial indicator in technical and economic aspect of rolling steel process. Its raising not only reduces the loss of metal and increases the amount of steel material, but also decreases the energy consuming. Especially in the current depressed market environment, increasing the rate is an effective means to reduce cost and improve profit for enterprises.In order to improve Q690D heavy plate’s yield rate for increasing the economic benefits, this thesis conducted a systemic study by using production statistic, trial and theory analysis, which focused mainly on the two main defects of the plate to cause more cutting loss, edge defect and bad plan shape, This study revealed the existing status, influencing factors, forming reason and controlling methods of the two defects and offered some measures for improving the yield rate of the plate.The main conclusions are as follows:First, the defects on the surface of this plate consist mainly of the transverse and longitudinal cracks at margin and non rectangular plan. They are respectively caused by the transverse crack survived on surface of slabs, inequality deforming in thickness direction and widening due to turning up, and the inhomogeneous deformation at head and tail of plate in the process of rolling.Second, the measures used in mold, such as optimizing regulation of the secondary cooling, adjusting the arrangement of the foot roller at narrow side, and setting copper plate with upside down taper, can control the loss of cutting plate edge with the transverse cracks.Third, the measures which include uniformly heating slabs, choosing suitable slab size according to the width of finished plate, and properly increasing the reduction of pass have been used for controlling the loss caused by cutting plate margin the longitudinal cracks.exist in.Moreover, decreasing the compensation value in width of PVPC can effectively restrict the drum belly of the plate, and then control its plan shape by optimizing the size of slab or reducing the rate of broadening. Meanwhile, it benefits in controlling tongue of the head or end of plates to decrease the compensation value in rolling direction.Finally, the yield rate of the plate is remarkably improved by applying these measures in site.