Research On QST Process Of Heavy H-beam After Rolling

The heavy H-beam is larger and thicker than the common hot-rolled H-beam.It is difficult to guarantee the performance of heavy H-beam by conventional controlled cooling process.The QST(on-line quenching and self tempering)process based on the Ultra-fast cooling technique provides a solution for the cooling of heavy hot rolled H-beam after rolling.In order to develop the QST cooling process of heavy hot rolled H-beam products with different flange thickness.This paper studies the QST cooling process by means of finite element simulation and experiment.Research work includes:(1)By using the finite element analysis software,the finite element simulation of temperature field of three kinds of heavy hot rolled H-beam is carried out under different QST processes.According to the simulation results of temperature field,the temperature drop law of each part of the section is analyzed,and the temperature field distribution of the section under different QST processes is explored.On this basis,the maximum temperature difference between the flange and the web can be controlled within 100? by adjusting the cooling strength of the web,so that H-beam can obtain a uniform section temperature field distribution.The temperature time curves of various parts in the process of controlled cooling of heavy H-beam with different specifications are drawn,and the QST controlled cooling process satisfying the conditions of self tempering is preliminarily developed.(2)By using the finite element analysis software,the displacement field of cooling deformation of heavy hot rolled H-beam after rolling is simulated.The influence of different cooling time on deformation and the influence of uneven cooling at different positions of H-beam are discussed.The deformation law of H-beam under different cooling conditions is obtained,and the solution of uneven deformation is put forward.The results of displacement field simulation show that the uneven cooling of web is the main cause of the uneven deformation;with the increase of ultra-fast cooling time,the degree of the uneven deformation of heavy hot rolled H-beam decreases.The simulation results of temperature field and displacement field are combined to provide the basis for making the best QST cooling process.(3)Under laboratory conditions,the experiment of quenching and self tempering on the 40mm flange heavy H-beam is carried out.The temperature field of material surface and 1/4 of thickness in QST process is measured by thermocouple.The temperature time curve is compared with the result of simulation.The results show that the two results are basically consistent,which verifies the accuracy of temperature field simulation.In order to study the effect of different QST process on the microstructure and properties,several groups of quenching and self tempering experiments were carried out by changing the quenching time in the UFC device.The results of microstructure and Properties Analysis of different quenching and self tempering processes are as follows:in QST process,with the increase of quenching time,the return temperature decreases and the thickness of tempering layer increases.When the return temperature is higher than 600?,tempered sorbite is formed.With the increase of quenching time,the strength and toughness increase,and the comprehensive mechanical properties decrease.When the return temperature of quenching and self tempering process is 600?,all aspects of properties meet the standard requirements,and the best comprehensive mechanical properties are obtained.