Numerical Simulation On Influence Of Oxide Scale Formation On The Slab Surface Temperature In Secondary Cooling Zone During Continuous Casting Process

Interacting relationship exists between the formed oxide scale and heat transfer on the slab surface during continuous casting process.On the one hand,the thickness and phase composition of oxide scale have great effect on the heat transfer coefficient of slab surface in secondary cooling and air cooling zones,which thus would change the heat transfer effect between the surface of hot slab and surrounding environment.On the other hand,the slab surface temperature is also determined by heat transfer effect between the slab surface and circumstance,which further affecting the formation rate of oxide scale as well as slab surface quality.Therefore,it is of great importance to make a thorough research about the influence of oxide scale formation on heat transfer on slab surface in secondary cooling zone to clarify the temperature variation of slab surface and improve the surface qualities during continuous casting.In the present work,on the basis of metallurgical kinetics and heat transfer theory,the formation rate of oxide scale and effective heat transfer coefficient of slab surface during continuous casting process were studied by taking the cast slabs of high Cu-containing and ferritic stainless steels as the investigating object.The temperature variations on slab surface with and without oxide scale formation were investigated,and the influence of oxide scale thickness on surface temperature was confirmed.In addition,the quantitative equation between the scale thickness of high Cu-containing slab and the parameters including casting speed,specific volume flow rate of cooling water in secondary cooling zone,and oxygen potential in atmosphere was established.The following results are concluded.Within the temperature range in secondary cooling zone,the thickness of oxide scale increases with the increment of surface temperature and residence time of casting slab in secondary cooling zone.The maximum formation rate of oxide scale for high Cu-containing slab is attained at the middle part of the secondary cooling zone,while it is at the upper part of the secondary cooling zone for the cast slab of ferritic stainless steel.In the present study,the heat transfer coefficient of scale layer formed on the slab surface of high Cu-containing steel is about 1.8?2.2W/(m·K),while it is about 2.1?3.2W/(m-K)for the scale layer formed on slab surface of ferritic stainless steel.The formation of oxide scale has a visible influence on the heat transfer coefficient in each part of secondary cooling zone.Compared with clean slab,the heat transfer coefficient on slab surface of high Cu-containing steel is reduced 1%?4%due to oxide scale formation,while 1%-6%reduction of surface heat transfer coefficient for ferritic stainless steel.The thickness of oxide scale is about 70 ?m at the end of secondary cooling zone for high Cu-containing steel;and it is about 50 ?m for ferritic stainless steel.The formation of oxide scale has a great influence on the slab surface temperature in secondary cooling zone.In the present work,the maximum temperature difference is about 15? between the slab with scale formation and the clean one for high Cu-containing steel,while it is about 20? for ferritic stainless steel.As for the same type of steel,the influence of oxide scale formation on surface temperature is greater at the central position compared with that at the corner.For the cast slab of high Cu-containing steel,the quantitative equation between scale thickness and the parameters including casting speed,specific volume flow-rate of cooling water,and oxygen potential in atmosphere is established.