During the steelmaking and hot rolling processes, various defects and cracks appear throughout the steel product. These cracks may initiate and grow throughout the hot rolling process and result in a lower quality of product than is acceptable. The most energy intensive part of the hot rolling process is the reheating furnace, where slabs are heated up to a target rolling temperature largely through radiant heat transfer. In the reheat furnace, large stresses may develop due to the thermal gradients within the steel product. Furthermore, even small cracks may propagate in the subsequent stages of the hot rolling process to produce unacceptable quality in the slab as well as cause economic hardships due to operations’ delay and possible damage to the equipment.

There have been quite a few research investigations previously done on reheat furnaces that have focused on the combusting flow in the furnace proper. The focus of this research is focused on the effect of the reheating process on the stress development within the steel slabs cause by thermal gradients. Of course, the thermal gradients are caused by the operating parameters of the reheating furnace, but most previous studies do not look into the stress generated within the slabs throughout this process. This stress, as previously mentioned, can play a large role in the quality of the final product. A better understanding of this phenomena could be used to increase the productivity or efficiency during the industrial process.

A thermal-stress analysis is proposed based on finite element method (FEM) to study the impacts of charging temperature, slab velocity, and heating rate on stress development as the steel slab travels through an industrial pusher-type reheat furnace. Furnace zone information is taken from a previously validated computational fluid dynamics (CFD) model and applied as thermal boundaries and constraints within the thermal-stress FEM models. Temperature and stress measurements were taken at the core, top, bottom, top quarter, bottom quarter of the steel slab at different residence times. Moreover, temperature lines and contour plots along the length of the slab allowed to visualize the gradual development of temperature and identify the locations corresponding to temperature variations as the slabs moves in the furnace. The slab temperature predicted by the FEM model was found valid when compared with industrial data. Stress predictions found similar trends with previously published works as well as evidence of thermal shock in the sub-surface near the beginning of the residence time. 

A good correlation between slab speed and charging temperature will lead to possible ways of reducing the residence time of the steel slab in the furnace. Various combinations of these variables will be considered to achieve the primary goal of maintaining a high slab quality with associated lower mechanical stresses.


Numerical Analysis of Thermal Stress Development of Steel Slabs in a Pusher-Type Reheat Furnace

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2020/volume/83709

18th International Conference on Nanochannels, Microchannels, and Minichannels
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Fluids Engineering Division Summer Meeting
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