| Due to the increase of Cr price in recent years, cost of stainless steel productionrises continuously. In order to decrease the production cost, a new type of low Creconomic duplex stainless steel （DSS）, called B2002with TRIP （Transformationindused plasticity） effect, was developed by Bao steel. B2002is expected to beapplied in automobile industry. However, this type of steel is still in the primarydevelopment stage, the influence of continuous casting process to its solidificationprocess and structure is still unclear and need to be studied further.Solidification structure of B2002duplex stainless steel with slab continuouscasting condition was simulated with a horizontal directional solidification equipment.The influence of pouring temperature and cooling intensity in secondary cooling zoneduring slab continuous casting process was simulated by changing superheat or waterflux, and the effect of forced convection was studied by imposing the horizontal orvertical mechanical vibration.In a given cooling rate, the results of thermal simulation showed that thesolidification structure of B2002was not sensitive to the flux change of the coolingwater and the superheat of melt showed a more obvious influence. The higher thesuperheat, the later the columnar to equiaxed transition （CET） took place. That was tosay, the equiaxed grains ratio decreased. The horizontal mechanical vibration had littleeffect on the CET position while the equiaxed grains were refined. In comparison, thevertical mechanical vibration had almost no effect on the solidificationmicrostructure.Numerical simulation of the above thermal simulation process was studied byProCast software. B2002DSS was simplified as a binary system, and theKurz-Giovanola-Trivedi （KGT） model was used for calculation. It was found thatgrowth factors5.0e-7，5.0e-7was suitable for the solidification structure prediction of hypothetic B2002. The results of numerical simulation showed that thecooling curves of samples with different superheat were almost the same. The changeof solidification structure was in accord with that in thermal simulation. Thetemperature gradient increased with the increase of superheat. This resulted in theincrease of the chill zone thickness and the columaner grans length. The temperaturegradient inside samples was comprehensively influenced by the heat transfer, meltsuperheat and the latent heat release during solidification. The solidification structurecould be predicted by KGT model. Due to the neglect of nucleus movement in thismodel, an obvious simulation deviation was found in the chill zone.Volume fraction of austenite phase at different positions in the B2002thermalsimulation samples was measured. The order of data collection was in accord with thesolidification process, i.e. from near the chill wall to the end of the sample. Theresults indicated that the content of austenite phase decreased gradually. Oneexception appeared at the CET position, where the content of austenite suddenlyincreased. As for the whole sample, the smallest grain size of austenite appared nearthe chill wall, where the highest austenite content reached almost65vol.%. Austenitein this zone nucleated and grown along grain boundary. This was different from thestructure of columnar grain zone and equiaxed grain zone, where the austenite highlydeveloped both along the grain boundry and inside grains. Austenite content in thesetwo zones were relatively low, with a amount about50vol.%. Since grains wereelongated in the colunamer grain zone, austenite there showed as Widmanst tten sideplates. While austenite in equiaxed zone showed as feather shape or dentritic shape. Ina word, water flux, superheat and mechanical vibration had little influence on thecontent of austenite. The distribution of autenite was related to the solidificationstructure and the position of autenite forming elements segregation. |
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