Improvement of Technology for Producing Rolled Sheet from Continuously Cast Steel Slabs. Part 1. Experimental Study of C
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IMPROVEMENT OF TECHNOLOGY FOR PRODUCING ROLLED SHEET FROM CONTINUOUSLY CAST STEEL SLABS. PART 1. EXPERIMENTAL STUDY OF CASTING USING A PRESSURE SUBMERSIBLE NOZZLE V. V. Stulov1 and A. V. Aldunin2
UDC 621.74.06
It is proposed to use a new submersible nozzle with eccentric apertures in order to improve continuously-cast slab quality. Calculations show that up to 38% of the heat of steel overheating is removed in the upper part of the crystallizer. The number of equiaxed crystals increases by several factors with an increase in crystallization rate. Pilot plant approval of advanced continuous casting of low-carbon and low-alloy steels makes it possible to improve hot rolled metal strength and toughness. Forecasting lowcarbon steel sheet ultimate strength and relative elongation is conducted using known experimental equations. Rolled steel quality is evaluated from slabs selected from eight melts. The slab sulfur content obtained using a nozzle with eccentric apertures is somewhat higher than in slabs cast through existing nozzles. Keywords: continuous-cast slab, casting nozzle, heat exchange, steel sheet, mechanical properties.
Improvement of technology for preparing rolled metal product is aimed at reducing the energy and resource content of metallurgical production. Currently this is an important task for Russian metallurgy [1]. In the traditional continuous casting process for workpieces of rectangular cross section with supply of molten metal into a crystallizer a pressureless closed-bottom submersible nozzle is used with oval apertures providing flow of a stream into the center of the device [2]. In this case values of melt velocity in wall layers of a crystallizer appear to be inadequate for increasing the workpiece crystallization rate. For the purpose of improving continuously-cast slab quality for steel workpieces a new production method has been proposed and also a device containing a closed bottom submersible pressured pouring nozzle with eccentric apertures [2, 3]. A metal flow scheme in the horizontal plane of a crystallizer during pouring through existing (Fig. 2a) and test (Fig. 1b) submersible nozzles with zones of the convective effect over extensive walls is shown in Fig. 1. In [2] the quality of the rolled sheet obtained from the slabs in question is inadequate, and at the same time its competitiveness depends on final product quality. It has been demonstrated in [2] that use of the new production method makes it possible to improve crystallization rate significantly (up to 50%) in a steel slab crystallizer, to reduce by a factor of 2–2.5 the zone of columnar crystals, and to increase by several factors the overall amount of equiaxed crystals. As a result of this without additional slab heat treatment the strength and impact strength of the metal obtained reach increased values [4]. In addition, an increase in crystallization rate within a slab is observed in the zone of convective effect in the upper part of a crystallizer bounded with slab surface at a distance of 15 mm from the workpiece surface
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