Effects Of Heating Process On Austenitizing Behavior In RE Microalloyed Low Carbon High Niobium Steel

With the development of modern physical metallurgical technology, low carbon highniobium steel is widely used at present. Whether Nb, Ti can full solid solution hasimportant influence on the control of microstructure and property after rolling in thesuccedent heat process. There are some researches showed that when rare earth is added inlow carbon high niobium steel, the equilibrium solid solution temperature of Nb decreasesand the solid solution of Nb increases, which is essential to saving energy and improvingthe utilization ratio of niobium. But there is little report about the effect of different REaddition on solid solution Nb, Ti and grain size of austenite. In this paper, the effect of rareearth on austenitizing behaviors of low carbon high niobium steel is investigated bycomparing the addition of rare earth with none addition of rare earth in low carbon highniobium steel. The effect on austenitizing behaviors of low carbon high niobium steel withdifferent rare earth content is compared. This research provides experimental data forenhancing the properties of rare earth microalloyed low carbon high niobium steel.The solid solution quantity of Nb and Ti of heated low carbon high niobium steeldetected by ICP, the original austenite structure captured by OM and the locations and thesizes of undissolved grain observed by SEM and TEM are analyzed to study The effect onsolid solution of Nb, Ti and undissolved second phase microstructure of low carbon highniobium steel with the different heating process and different amount of rare earth.The experimental results illustrate that1the solid solution proportion of Nb in the teststeel with no rare earth is respectively increased from23.6%to51.4%; the solid solutionproportion of Ti in the test steel with no rare earth is respectively increased from10.5%to41.0%. The solid solution quatity of Nb and Ti in the test steel containing rare earth hardlychanges after different processing, the solid solution proportion of Nb maintained at about75%, the solid solution proportion of Nb maintained at about55%. the average grain sizeof test steel with64ppm rare earth is respectively increased by13μm compared with theone with no rare earth after1h isothermal holding treatment at1250℃.The solid proportion of Nb and Ti in the test steel with64ppm rare earth are respectively improved54.1%and44.9%compared with the one with no rare earth after1h isothermal holdingtreatment at1250℃.The average grain size of test steel with rare earth is almost the samecompared with the one with no rare earth, but the solid proportion of Nb and Ti in the teststeel with rare earth are respectively improved25.5%and13.7%.The solid proportion of Nb and Ti are unnoticeable in the same temperature of the teststeel with different contents of rare earth, and reached a rough balance after40minisothermal holding treatment at1250℃.The average grain size of the two kinds of teststeel with different contents of rare earth is small when the heating temperature under1250℃. When heating temperature changes from1280℃to1300℃, the average grainsize of test steel with40ppm rare earth is respectively increased by8.4μm and28.1μmcompared with the one with6ppm rare earth.