SynopsisThe cooling process of a hot steel plate by a cylindrical water flow was studied experimentally and analytically in this paper.The cooling characteristics were examined on the basis of cooling curves obtained under various experimental conditions. A numerical model was built up to calculate the relation between temperature and time at a given point of the steel plate during cooling. Then, the heat transfer coefficient on the water cooling zone was found out so that the cooling curve calculated by the numerical model became equal to the experimental result.The main results obtained in this paper are as follows:(1) The heat transfer coefficient on the water cooling zone may be considered to be proportional to square root o f the defence between the plate surface temperature and the water temperature;where, BS, Bw : The temperature of the plate surface and the cooling water, respectively.(2) The black zone is formed on the initially hot red plate surface, as soon as the water strikes the plate. The radius of the black zone expands approximately in proportion to square root of the cooling time.(3) The theoretical cooling curves were found to match with the experimental ones by the appropriate combination of the heat transfer coefficient on the water cooling zone and the growth rate of the zone. Here, a=500 (0S-o )'~2 as the heat transfer coefficient (kcal/m2h°C) and Rw=RB+10.0 as the water cooling radius (mm) were used in this calculation, where RB indicates the black zone radius.

The film boiling phenomena on a hot steel plate are experimentally and theoretically analyzed in due consideration of the interaction between the cooling water and the plate surface temperatures, when a relatively hot water bar impinges on the plate surface.

A predictable model to estimate the true stress‐true strain response of plain carbon steel has been made being divided into the two ranges of α‐ and γ‐iron respectively. Again, for the (α + γ)‐range, the mass fraction of the two phases has been taken into consideration. As a result, the peak stress as well as the stress‐strain relation calculated by the model have been found to be in fairly good agreement with those measured by a few investigators under various temperature and strain rate conditions. In particular, concerning the peak stress, it has been confirmed that the model gives a remarkable good conformability, compared with the measured values. Also, the peak stress exhibits the discontinuous change at the A3 point. However, with an increasing carbon content, the discontinuous point tends to shift toward the lower temperature side, and the changing degree becomes slighter.

SynopsisThe length of the rolling mill line and the slab temperature change are theoretically compared between the quasi continuous type equipped with 3 rougher mills, of which the first one is reversible, and 6 finisher mills and the quasi continuous 4 passes type equipped with 2 rougher mills, of which the first is reversible, and 6 finisher mills for a mathematical model that a slab is rolled from the initial thickness 230 mm to the final thickness 2.5 mm.In the quasi continuous 4 passes type, the total length in the roughing process can be shortened to about 60% compared with the case of the quasi continuous type. For a given reheating temperature, the slab temperature at the entrance of the first finisher remains much higher in the quasi continuous 4 passes type so that the reheating temperature can be reduced over 100°C. Finally, one conclusion is that the quasi continuous 4 passes type is much profitable not only for the shortness of the rolling mill line but also for the energy saving in the rolling process.

A numerical model is proposed to predict the cooling process of a hot steel plate by a laminar water bar. This model gives a close agreement with the experimental cooling history for arbitrary water flow rate and water temperature.