Occurrence State of Niobium and Titanium in High Pure Ferritic Stainless Steel

摘要

As stabilization elements added into high pure ferritic stainless steels,niobium and titanium react with carbon and nitrogen to form carbonitrides and promote their mechanical properties and corrosion resistance.Occurrence state of niobium and titanium is the first problem need to be solved.Therefore,combined with thermodynamic calculation by FactSage software,occurrence state of niobium and titanium in high pure ferritic stainless steel was investigated by optical microscope,scanning electron microscope,transmission electron microscope and energy disperse spectroscope.Results show that niobium and titanium exist as carbonitrides and solid solution except for a certain quantity titanium oxides.The additions of niobium,titanium,carbon and nitrogen have great effect on the precipitation temperature of carbonitrides and titanium oxides.Titanium oxides precipitate firstly and the precipitation temperature is higher than the liquidus of steel,and its carbonitrides precipitate secondly at the temperature near the liquidus,carbonitrides of niobium precipitate at a relatively lower temperature below 1200°C.