Study On Control Technology Of Cold-Rolled Strip Slivers Of Precision Alloy Ni42 Caused By Steelmaking Process

The precision alloy Ni42 cold-rolled strip is a kind of high precision product,and users always have high strict quality requirement on this product.Precision alloy is firstly produced by the route of EAF-AOD-LF-VD-CC in Baosteel Special Steel Co.,Ltd.of China,which is also the second enterprise of worldwide.The sliver defect is the main problem of cold-rolled strip of Ni42,however,there is no related mature technology for reference in domestic or foreign countries.Therefore,it is necessary to analyze the cause of sliver defect in order to obtain a critical process technology of precision alloy Ni42 for the enterprise.In the present paper,liquidus and solidus temperatures,thermal expansion coefficient,density,specific heat,heat conductivity and high temperature properties of Ni42 have been conducted by DSC,quartz rod type dilatometer,hydrostatic method,balance weighing method and Gleeble-3800 equipments,respectively.Then,the critical influential factors on non-metal inclusions and mold slag entrapment in precision alloy Ni42 produced by the route of EAF-AOD-LF-VD-CC were investigated using metallographic and scanning electron microscopy method.The key points of steelmaking process included controlling carbon and oxygen in AOD,composite deoxidation by Al and Si,slag washing,VD refining process and controlling technology of mold flow field.Finally,the cold-rolled strip of Ni42 owing to steelmaking process has been decreased significantly after industrial application.The main conclusions of the present paper are these:(1)The sliver defects of cold-rolled strip on precision alloy Ni42 were mainly caused by the inclusions with poor deformation ability and mold slag entrapment.(2)The original content of carbon in EAF has increased to above 2.5%.When AI content was more than Si content,the final oxygen content decreased to below 0.0035%.The reduced slag was changed at the final stage of AOD and prolonged the vacuum time of VD in order to improve the slag mixing effect and decrease the contents of hydrogen,oxygen and nitrogen.(3)The numerical simulation results showed that the revised SEN of type C was better than the original.The ideal immersion depth of SEN was between 110 and 120 mm,which can decrease the mold level fluctuation and mold slag entrapment.(4)The average total oxygen content of slab decreased from 0.0030%to 0.0019%,and the corresponding defect rate of cold-rolled strip decreased from 36.87%to 9.02%by applying above measures from 2012 to the first quarter of 2016.