Emissivity and oxidation evolution in reheating furnace environments

加热炉是塔塔欧洲钢铁公司热轧厂的重要组成部分。加热炉由燃气燃烧器加热，目的是通过厚度将钢板加热到已知的轧制温度。加热炉主要依靠热量辐射传递到坯上。由于钢容易氧化，钢坯表面就会形成氧化层。这对从炉子到板坯的热传递有两个主要影响：它改变了表面的发射率，从而改变了板坯从炉子吸收的能量。它在板坯表面引入了一层绝缘层，减缓了热扩散到板坯中的速度。简单钢的氧化层厚度可以近似计算，但发射率随时间和温度的变化及其对氧化层厚度或氧化层表面拓扑结构的依赖是未知的。众所周知，氧化鳞片的发射率受许多参数的影响，包括气氛的组成、钢的等级、温度、钢的表面状况和时间。其中一些参数是在我们的控制范围内的，例如，加热炉中大气的成分，温度循环或钢的成分。在这个项目中，我们想了解温度循环和最终炉内气氛如何影响氧化垢的表面状况，从而影响发射率。第一个工业目标是能够在炉模型中引入准确的发射率值，作为时间和温度的函数，第二个目标是将这种预测外推到不同的钢成分。如果时间允许，另一个目标是了解如何控制发射率以最大限度地提高其效率。该项目的目标包括：开发和验证一个实验装置，可以测量氧化鳞片的发射率作为温度和时间的函数。测量在代表加热炉气氛的环境中加热的HSLA和低碳等级的发射率作为温度和时间演变的函数。将发射率的变化与氧化层的变化联系起来，例如形态、结构或成分的变化。制定工业模型中使用的发射率，时间，温度和钢成分的关系。建议，如果时间允许，优化炉参数，或板坯表面修改，以达到最大的板坯发射率。

Reheating furnaces are an essential part of Tata Steel Europe's hot mills. Reheating furnaces are heated by gas burners and aim to heat the steel slabs to their rolling temperature with a known temperature profile through the thickness. Reheating furnaces rely predominantly on heat being radiatively transferred to the slabs. Since steel is prone to oxidation, the slabs grow an oxide layer on their surface. This has two major effects for the heat transfer from the furnace to the slab: It changes the emissivity of the surface, and therefore the power the slab absorbs from the furnace. It introduces an insulating layer on the surface of the slab, which slows thermal diffusion into the slab. The oxide layer thickness can be approximately calculated for simple steels, however the evolution of emissivity with time and temperature as well as its dependency on the oxide thickness or topology of the oxide surface is unknown. The emissivity of oxide scales is known to be affected by a number of parameters, including the composition of the atmosphere, steel grade, temperature, steel surface condition and time. Some of these parameters are within our control, for example the composition of the atmosphere in the reheating furnace, the temperature cycle or the steel composition. In this project, we would like to understand how temperature cycle and eventually furnace atmosphere affects the surface condition of the oxide scale, and therefore the emissivity. The first industrial aim is to be able to introduce accurate emissivity values in the furnace model as a function of time and temperature, the second aim is to extrapolate this prediction to different steel compositions. An additional aim, if time permits, is to understand how to control the emissivity to maximise it and improve furnace efficiency. The objectives of the project include: Develop and validate an experimental setup that can measure the emissivity of oxide scales as a function of temperature and time. Measure emissivity as a function of temperature and evolution in time for HSLA and low carbon grades heated in an environment representative of a reheating furnace atmosphere. Relate emissivity changes to changes in the oxide layer, e.g. morphological, structural, or compositional changes. Formulate the relation emissivity, time, temperature, and steel composition to be used in the industrial model. Suggest, if time permits, the optimised furnace parameters, or slab surface modifications to achieve maximum emissivity on the slabs.