Generation Mechanism And Control Technology Of Tin Inclusion For GCr15SiMn In ESR Process

Bearing is the key part on Tunnel Boring Machine(TBM).In this paper,it puts stress on bearing steel GCr15SiMn used on TBM.In steelmaking BOF/EF-LF-VD/RH-IC-ESR,it notes that in the electrode and ingot during Electroslag Remelting(ESR),large single and complex titanium nitride are the main character in this steel,which will worsen its properities.In the present study,the Confocal Scanning Violet Laser Microscope(CSLM)cooperated with mathematical models are employed to investigate the behaviors of titanium nitride in this steel during ESR.The confocal display shows that after the temperature reaches some degree higher than the steel solidus temperature 1583 K(1310?),titanium nitride in the electrode specimen begins to dissolve.Higher temperatures lead to faster dissolution and the 10 ?m inclusion disappears at 1691 K(1418?)before the steel is fully liquid at 1733 K(1460?).This kind inclusion found once more,if it is,in the subsequent ingot is regenerated,not from the electrode.Through mathematical model,it notes that during solidification of steel in ESR,after titanium nitride precipitation,titanium in liquid steel will decline with solid fraction,while nitrogen still increases,but with a lower slope.Narrow the gap between the liquidus and solidius temperatures will delay the onset of titanium nitride precipitation,and hence decrease its size as well as the amount of complex titanium nitride.In confocal microscope for complex titanium nitride,upon precipitation,an obvious growth of titanium nitride on the oxide particle is observed due to the rapid solute diffusion in liquid steel.The onset of titanium nitride precipitation does not change with the oxide particle size(1648 K(1375?)for 10 ?m and 1643 K(1370?)for 5 ?m oxide particles).Meanwhile,the particle size displays little influence on the total precipitated amount of titanium nitride on it under the same conditions(volume change 1197 ?m for 10 ?m and 1033 ?m for 5 ?m oxide particles).The lack of inclusion size change near the end of solidification suggests that heterogeneous nucleation on the oxide particle lead to depletion of titanium and nitrogen prior to the completion of solidification.Therefore the presence of the oxide particle will play an important role in determining the temperature regimes in which titanium nitride inclusion grow.Near the end of solidification,the inclusion shape varies from circle to almost square in two-dimension,or cubic in three-dimension,in order to reach the equilibrium with steel.Through plant trial,it gets that compared with others,SiO2 in the slag has relative large effect on the titanium in steel.Increasing SiO2 in the slag will decline titanium in steel.Corresponding to titanium in slag,there is an equilibrium critical value in steel,the titanium in steel will approach this critical value spontaneously through oxidation or rise.