Development Of Flexible Roll Accelerated Cooling Device And Its Application In Annealing Of Stainless Steel Strip

430 ferritic stainless steel has good corrosion resistance,mechanical properties and forming properties.It is easy to make beautiful parts.It has good application prospects in automobile exhaust pipe,kitchenware,household appliances and other fields.Aiming at the main problems existing in cooling stage of stainless steel traditional annealing process,this paper focuses on solving the problems of unsatisfactory heat transfer effect,low cooling speed and lack of special contact cooling device.The micro-structure and properties of products under different annealing temperatures,different flexible roll speeds and different cooling methods were studied by using the flexible roll controlled cooling device independently developed by the research group.At the same time,the cooling effect of the flexible roll was analyzed comprehensively in order to explore suitable application objects and reasonable process parameters for the flexible roll cooling device,and accumulate valuable experimental data for its industrial popularization.The research contents and main conclusions of this paper are as follows:1.Based on the theory of heat conduction and rolling friction contact,the flexible roll accelerated cooling device was developed,and the wall thickness of roll sleeve and transmission mode of the device were optimized.The cooling effect of the flexible roll was analyzed by combining the thermometer data.When annealing temperature rising from 400? to 1100?,the cooling speed of strip steel increased gradually from 212?/s to 497?/s;when the linear speed of flexible roll increased from 0.02m/s to 0.1m/s,the cooling speed of 0.3mm stainless steel strip gradually increased from 205?/s to 571?/s;and for 0.5mm stainless steel strip,the cooling speed gradually increases from 210?/s to 689?/s,which shows that for thicker strip,the cooling speed is accelerated.The reason is that the increase of the pressure between rolls which affects the heat transfer coefficient results in the acceleration ofthe cooling rate because of the same conditions in the roll gap.2.The influence of flexible roll cooling device on the cooling efficiency of strip at different annealing temperatures was analyzed by thermometer,and the micro-structure and properties of strip were analyzed by tensile testing machine,OM,SEM and EDS.The results show that the grain size of the product is greatly affected by annealing temperature.The content of Cr in the matrix of the product changes a little,but the content of Cr along the transverse direction is uniform at different temperatures,and no segregation phenomenon is found.The strip steel obtains better mechanical properties when annealed at 850?~900?.At this point,the strength is greater than 490 MPa,the elongation is greater than 22%,and the yield-strength ratio is about 0.58.3.The micro-structure and properties of 0.3mm and 0.5mm products cooled under different linear velocity of flexible rolls were analyzed.The results shows that the 0.3mm strip steel obtains better comprehensive mechanical properties at the roll speed of 0.06m/s,with fine grains and uniform equiaxed shape,which avoids the phenomenon of Cr depletion at grain boundary.The corrosion resistance and comprehensive mechanical properties of the 0.5mm strip steel are better at the roll speed of 0.02m/s.4.The cooling effect of strips under different cooling methods in annealing process was tested and analyzed.Six different cooling paths were combined spray cooling,roll cooling and air cooling to test the average cooling speed.The results were as follows: first roll cooling + spraying water > first spraying + roll cooling >spraying water > first roll cooling + blowing air > first blowing + roll cooling >blowing air.The typical cooling effect was as follows: The cooling rate of first roll cooling + spraying water is 37.8 ?/s and the cooling rate of blowing air is 11.4 ?/s.5.The micro-structure and properties of strip steel under different cooling methods were analyzed by uniaxial tensile testing machine,OM,SEM and EDS.The results show that the ferrite grain size of strip steel varies with different cooling methods,but the change is not significant.The distribution of Cr in the matrix is uniform under different cooling methods.The formation of chromium carbides causes the content of chromium in the matrix to be satisfied from more to less: first roll cooling + spraying water > first roll cooling + blowing air > first blowing air +roll cooling > spraying water > blowing air.The tensile strength of product obtainedunder combined cooling methods is maintaining at 500 MPa,the yield strength is below 295 MPa,and the combined cooling methods can reduce the yield strength ratio to 0.583.