Research On Controlled Cooling Technology Of Large Flat Spherical Steel

Flat steel is a profiled section structure widely used in Marine ship and bridge construction.It consists of two parts: bulb and web.Large flat steel ball because the ball head and web size is large,the non-uniform deformation occurring in the process of rolling,deformation degree of each part is different,the cooling speed of each part in the process of cooling,the ball flat steel internal organization big differences,uneven temperature distribution at the same time also can cause the ball flat steel bending,torsion,which affects the ball flat steel mechanical properties and dimensional accuracy.Therefore,the influence of different control cooling process parameters on the internal structure of DH36 spherical flat steel produced by a domestic enterprise was studied.The results of microstructure observation of DH36 spherical flat steel show that there is serious inhomogeneity in the microstructure of spherical flat steel.The grain size of the side of the ball head is about 17.6 ?m,the grain size of the hypotenuse is about 12.5 ?17.9 ?m,the grain size of the bottom is about 18.9 ?25.0 ?m,and the grain size of the core is about 18.5 ?25.0 ?m.Using the designed cooling device,the ball flat steel mixed gas water cooling and water cooling experiment was carried out,after cooling of the each part of the ball flat steel microstructure were observed,the results show that the mixed in the gas water cooling condition,the ball flat steel ball head cooling rate on the surface of the lowest 14.3 ?/s,up to 24.8 ?/s,heart of maximum cooling rate is 14.5 ?/s,ball head and web maximum differential cooling rate is 11.5 ?/s,ball head grain size about 40 microns.Under the condition of water spray cooling,the cooling rate of the surface of the ball head is 19.7 ?/s,the maximum cooling rate of the core is 22.8 ?/s,and the maximum cooling rate difference between the ball head and the web is 26.4 ?/s.The grain sizes of side edge,hypotenuse edge,bottom edge and center of the ball head are 10.0 ?m,12.5 ?m,14.3?m and 15.2 ?m,respectively.Compared with the air-water mixed cooling,the cooling rate of the water-jet controlled cooling is increased.Compared with the rolled state microstructure,the microstructure is obviously refined after the water-jet cooling.It can be seen that the water-jet cooling process and cooling device designed in this paper have better cooling effect.