Study On The Bloom Surface Quenching Of Cold-heating Steel SWRCH22A During The Hot Transfer Process

The application of heat transfer technology can efficiently reduce energy consumption in the process of iron production.For certain steel,hot cracking will easily come out when it is two-phase temperature.The heat history of billet surface is changed by the on-line quenching technology,which could effectively solve hot crack problems among low carbon aluminum steel,high strength low alloy steel and others,which at the same time,could keep heat transfer temperature high,saving energy effectively.The paper researched heat transfer process of certain casting bloom containing aluminum made of cold heating steel.It came up with the change law of temperature field,surface microstructure followed the process parameters during surface hardening process,under the condition of the establishment of mathematical model and laboratory simulation experiment at the process of the quenching and temperature recovery,the main conclusions are as follow:1.The precipitation of aluminum nitride has a great influence on the thermal cracking.According to the calculated formula of solid solubility on Al containing cold heading steel,AIN precipitation temperature was in the range of 1033?-1155?,lower than 1200O.The PTT curves of AIN particles precipitating in the austenite and nose point temperature were obtained by theoretical calculation.For uniform nucleation,dislocation nucleation and grain boundary nucleation mechanism,the temperature of which were separately 820?,820? and 920?.2.The surface temperature of cast billet decreases rapidly when surface quenching technology was adopted.At air cooling stage,temperature of slab surface backed up,when reaching the highest point the overall temperature of slab began to fall until the billet was sent to the furnace.During the quenching process,both the increasing of the casting speed and the increasing cooling water flow could increase the temperature drop of slab surface while not with the inner part.Compared with casting roller hot delivery process,temperature change of the billet core was the same,however,change law of surface temperature varied greatly.3.Cooling water flow and cooling time can achieve the required cooling effect,appropriate surface cooling rate and quenching layer thickness.While the cooling water flow rate and cooling time was restricted by rolling speed,casting speed and cooling zone length.For the experiment of cold heading steel billet,cooling water flow being 500L/min and casting speed being 2m/min was the optimum quenching process.The relationship of spay flow rate,initial temperature and cooling speed is researched.4.The microstructure and quenching temperature of the billet surface were related to T,when T?Ar3,mainly martensite;when Arl<T<Ar3,mainly proeutectoid ferrite and martensite;when T<Ar1,mainly ferrite and pearlite.After being heated,the austenite grain size was not affected by quenching temperature.The billet surface quenching process compared with hot delivery roller technology,the microstructure of slab was different when casting and the size and distribution law of austenite was different after being heated.