Research On Rolling Process Of The Heavy Steel Plate And The Formation Mechanism Of Defects Detection

In recent years, with the rapid development of national economy and the increasing of building super high-rise and large-span steel construction projects, the demand for heavy steel plate with more heavy thickness and better properties used in construction and machinery has been increasing. At present, China’s more than100mm heavy steel plate mainly uses the molded ingot to manufacture. This method exists problems of long manufacturing cycle, high energy consumption, high production costs, poor work environment and so on, more and more can’t meet the need of economic development. Using of thickness continuous casting slab manufacture the heavy steel plate has high rolling yield, high production efficiency, good working environment, the relatively lower energy consumption, be more and more steel enterprise’s choose. This method to product the heavy steel plate is the trend of The Times. In recent years, some steel enterprise in China, such as ShouQin, NanYangHanYe, XinYu and so on, built a group of400mm thick steel plate continuous casting machine, these created hardware conditions for the use of casting billet production manufacturing heavy steel plate. This paper was supported by a steel enterprise, the main purpose is to carry out industrial test research of manufacturing more than100mm steel plate using400mm continuous casting slab. Chief original work is as follows:(1) Conducted the industrial trials of hot rolling105-160mm Q345steel plate.Using the ordinary C-Mn steel, take measures of the increase of billet heating time, reasonable lane of reduction design, rolled slow cold process and so on, we successfully use300mm casting billet produce105mm Q345E-Z35steel plate, steel plate center average impact energy reached98J in-40℃conditions, average Z-direction section shrinkage reached42%. Using400mm casting billet successfully produce130mm Q345D-Z25steel plate and150,160mm Q345C-150steel plate.(2) Conducted the industrial trials of more than100mm Q345q bridge steel. Using the ordinary C-Mn steel, take measures of reasonable lane of reduction design, rolled slow cold process and so on, we successfully use400mm casting billet produce110mm Q345qD-Z35steel plate, steel plate center average impact energy reached50J in-20℃conditions, average Z-direction section shrinkage reached38.5%.(3) The detecttion defects characteristics in the steel plate production was analysised. By comparative analysis of the characteristics of the flake and hydrogen brittleness defects, the main reasons causing the detection defects were determined to be the effects of hydrogen and inner stress, and the research direction on the formation mechanism of the detection defects was proposed。(4) The diffusion hydrogen characteristics in steel was analysised, and a mathematical model of steel plate internal hydrogen diffusion escaping was established. According to this model, the influence of each technological art on the hydrogen diffusion was also analysised. The results show that:the greater the thickness of the steel plate, the more difficult the hydrogen diffusion; In the air cold process,20mm of the steel plate most of internal hydrogen can be natural way to escape, the effects of hydrogen is very limited; More than20mm steel plate internal hydrogen diffusion escape from the steel is limited, need to take slow cold measures to row hydrogen.(5)By finite element numerical simulation method, based on the hot elastic-plastic mathematical model, the transient temperature field and stress and strain field in heavy steel plate accelerated cooling progress are simulated. In the water cooling progress, the heavy steel plate internal can have a huge temperature gradient, cause the inhomogeneity of the phase change, cause internal produce larger residual stress. When the cold speed of steel plate is relatively fast, the residual pressure stress on the surface, the heart of the characteristics of the tension. when cold speed is relatively slow, steel plate internal residual stress on surface and center under pressure, a quarter in thickness by tensile stress.