Ying Zhi

Rolling Technology with Reducing Resources in China

In recent years, steel production has increased rapidly in China, to approximately 489 Mt in 2007. However, any further growth in production presents problems related to the shortage of energy and resources, environmental pollution, and the high cost of raw materials. In view of this, the government of China has changed its steel policy from tax return for export of steel products to adding extra tax on it. The steel companies in China are now forced to devote more attention to reducing the cost of steel production. This articleputs forward idea of rolling steel with declining resources. It includes: 1) Flexible Rolling Technology (FRT) based on the technology of online control of microstructure and properties, which will facilitate using a slab with the same chemical composition to produce the steel products of different properties by means of using different rolling and cooling parameters; 2) new generation cooling system and new generation Thermo-Mechanical Control Processing (TMCP), including High Rate Cooling (HRC) and Cooling Path Control (CPC) for plate mill, hot strip mill, and bar mill; 3) development of high performance steel products with low cost, such as super steel, fine grained steel, and Advanced High Strength Steel (AHSS), such as Dual Phase (DP) and TRIP steels with simple chemical composition. The key points are to save energy and reduce resource consumption (especially the consumption of microalloying elements), aiming at reducing manufacturing cost and helping to protect and conserve the environment, which is considered to be the best way to ensure sustainable development of steel rolling industry.

Horizontal Velocity of Variable Gauge Rolling: Theory and Finite Elements Simulation

Within the production chain of longitudinal profiled (LP) plates and tailor rolled blanks (TRB), variable gauge rolling (VGR) represents the vital important forming stage, in which shape and properties are tailored to satisfy customers’ requirements. It is of vital importance to reveal the relationship between work-piece horizontal velocity and roll vertical velocity during VGR, which is not only a key point to understand the deformation law, but also an important content for setting VGR process parameters. It is proved that the simplified assumption of equal discharge per second condition (EDSC) breaks down during VGR. Due to this reason the differential equation of the work-piece horizontal velocity (VGR-V) is performed by keeping the material volume constant. To attain a comprehensive understanding of this underlying process in detail, numerical approaches based on finite elements method have been performed by utilizing the Abaqus Explicit. Rolling experiment is carried out which indicates that the numerical result coincides with the experimental result well. A fine spatial discretization of work-piece is essential for special emphasis has to be put on detecting different horizontal velocity of work-piece cross section, often leading to a hundred thousand degrees of freedom even for plane strain calculations. The data obtained by using Abaqus Explicit coincide with the results determined by theory. A theoretical basis on deformation parameters and mechanical parameters during VGR process is provided.

Re-reddening on Strip Surface After Water Cooling

After water cooling, there is a big temperature difference between the center and the surface of strip, which leads to the heat transfer from the center to the surface, and the surface temperature can rise in a short time. The finite element method was used to simulate the phenomena of re-reddening on the surface of strip and to analyze the temperature field of hot rolled strip during laminar cooling, and the periodical variation curve of the cooling rate was obtained during water cooling and subsequent re-reddening. The results show that the critical line of the cooling rate is at 1/3 of the half-thickness from the strip surface. The regression model of the relation of re-reddening temperature, time, and distance from the surface was obtained in the re-reddening region. Re-reddening regularity on the surface of strip under the condition of different thickness and cooling rate was also studied.

An Inverse Method for Equivalent Gray Gas Radiation Characteristic Parameter

Compared with non-gray model, equivalent gray model has equal calculation accuracy but much higher computing speed. To solve the existing problems of the equivalent gray method, sole ternary model was developed. In the model, coupling solving process of energy balance equations is omitted and the model zone is real closed. Meanwhile, the full furnace temperature and heat flow calculations are avoided, which makes it easier to find the relationship between the equivalent gray gas radiation characteristic parameter and the initial conditions. The radiation characteristic parameter was calculated with different temperature combinations, different model zone sizes and different partial pressures of absorbent gas. The results show the similar variations in the absorption coefficient and emissivity for the equivalent gray model, which both decrease with the increase of the gas temperature and the surface temperature (especially the former one) as well as the model zone size while increase with the increase of the partial pressure of absorbent gas.

Influence of Edge Rolling Reduction on Plate-Edge Stress Distribution During Finish Rolling

Dimensions of one kind of stainless steel plate before finish rolling were obtained through analysis of the rough rolling processes by finite element method and updated geometrical method. The FE models of finish rolling process with a front edge roll were built, and influences of the edge rolling reduction on the stress change in the plate edge during finish rolling were analyzed. The results show that when the edge rolling reduction is increased from 0 mm to 2 mm, the compressive stress in plate corner clearly increases in edge rolling process, and the zone of tensile stress during whole rolling decreases; when the edge rolling reduction is increased from 2 mm to 5 mm, the compressive stress in the plate corner seldom changes, and the compressive stress decreases after the horizontal rolling.

A New Simplified Zonal Method for Furnace Thermal Radiation Calculation Based on Imaginary Planes

When solving the complex radiative heat transfer problems in reheating furnaces, there are a number of difficulties with the traditional zonal methods. To circumvent these difficulties, a new simplified method was proposed, which employed imaginary planes, referred to as the imaginary plane model With the new model, crown wall reduction process was simplified. Therefore, every model zone could be treated as a closed square cavity, It could also solve the problem of radiative blocking in industrial furnaces more effectively. Besides, the new imaginary pla.D.e based model may lead to a problem that the denominator was zero. This problem was solved by transforming the expressions of reflex heat flux in the model. The model was capable of dealing with the systems that included black surfaces. The model was validated by considering the heat transfer in a reheating furnace where the temperature fields in the furnace chamber (including the steel, wall and gas) were obtained. A detailed comparison was made between the simulation and the black box experiment. The results show that the new model developed was valid and accurate.