| The strong quenching has the ability of improving the strength,hardness and wear resistance of metal.It has been widely used in steel production and application,but the research and application in ductile iron has just begun.With the rapid development of computer technology and the increasing demand of quenching quality,the computer finite element analysis technology has become an indispensable part of quenching technology research.This paper aims to solve the problem of lack of strong quenching tank by combining the computer finite element analysis technology with experiment,and to study the best quenching technology of ductile iron.In order to solve the problem of lack of strong quenching tank,a double vortex quenching tank and its accessories are designed to form a strong annular flow field around small members with variable cross-section,which can make the effect of strong cooling.The quenching tank accessories can realize the medium circulation in the quenching system,and the quenching process is free of splash.In this paper,through the experiment of the strong quenching of ductile iron,it is found that the residual pressure stress of the surface of ductile iron can be formed from-102.4MPa to-354.4MPa after the quenching.The range of the velocity of quenching medium in this experiment is obtained.It is proved that the quenching medium velocity is more than 1.4m/s in the design of quenching tank,and the quenching effect can be formed.Under the condition of surface velocity,a variety of quenching tank models are designed by using finite element analysis software and the optimal model is obtained by comparative analysis.The finite element analysis of the computer is carried out firstly by the coupling of flow and heat,then the transient and transient thermal finite element analysis results are used as the boundary conditions of the finite element model to realize the finite element analysis of the intense quenching process,namely,the coupled finite element analysis of the flow field temperature field stress field.The simulation results show that the liquid medium flow forms double vortex fluid in the quenching tank,and the high-speed circulation field around the work piece can be formed at the intersection of the vortex.The decrease of the velocity at the inlet of the quenching tank will reduce the medium velocity around the nodular iron columnar work piece.When the flow rate around the work piece is greater than or equal to 1.4m/s,the designed strong quenching tank can form a better quenching effect on the ductile iron work piece.When the velocity of the inlet of the quenching tank is 4m/s,the flow velocity of the ring flow field can reach2m/s,which makes the cooling speed of the nodular iron sample reach 520℃/s,The crack formation rate is almost zero.The results show that the uneven velocity of medium in quenching tank causes the uneven distribution of temperature field in the cylindrical work piece of nodular iron,the temperature at the edge of the bottom of the specimen decreases rapidly and the cooling speed is the fastest.The surface of the specimen is cooled rapidly and the center part is still at high temperature,so the surface is hardened to form a hard shell.The stress field is analyzed to show that the cooling of the columnar work piece of nodular iron is uneven in the quenching bath.A large number of martensite structures are formed in the middle part of the column due to high-speed cooling.The residual pressure stress on the surface is about-234.85 MPa,and there is no surface residual pressure stress at both ends of the column.The optimal quenching time is 1.1s compared with the stress field under different quenching time. |
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