Investigation On Solidification Microstructure Of Continuous Casting Billet Of 42CrMo Gear Steel

Gear steel is a kind of special steel with large quantity and wide area.It is an important material for manufacturing automobile gears,industrial gears,gear devices and other parts of transmission system.Gear steel needs high reliability,long life,impact resistance,wear resistance and other properties.By strengthening the metallurgical quality control of gear steel,the process performance and service performance can be improved,and the product quality stability can be improved,so as to achieve high performance.Through the study of the solidification mechanism of slab,the growth and evolution of the microstructure of slab solidification are analyzed,which is of great significance for optimizing the on-site continuous casting process.In this paper,42CrMo gear steel billet is taken as the research object.Infrared temperature measurement experiment,low magnification test experiment,dendrite corrosion experiment and grain corrosion experiment are carried out,together with numerical simulation technology,the solidification behavior and microstructure of 42CrMo gear steel billet are studied,and the solidification structure growth of billet is also studied.Based on the analysis and summary of the law of behavior and evolution,the rules of growth and change of tissues with different superheat and casting speed are explored.The main contents and achievements of the research are as follows:(1)Infrared thermometry was used to measure the temperature of the surface center of the billet.The temperature at the three locations between the exit of the secondary cooling chamber and the stretching straightener was 1032.9?,1002.4?and 990.1?,respectively.(2)The dendrite structure on the slab surface was studied by low-power corrosion technology.The area of each crystal zone was 13.46cm2,21.93cm2,19.87cm2 and 12.8cm2 in the surface fine-grained zone,columnar zone,mixed zone and equiaxed zone,respectively.(3)Dendrite corrosion experiments were carried out.The secondary dendrite arm spacing values at 15mm,35mm,55mm and 75mm from the slab surface are in turn:78.56?m,126.37?m,159.64?m and 197.73?m,respectively.(4)Grain corrosion test was carried out.The average grain area at 15mm,45mm and 75mm from the slab surface is in turn:0.50mm2,0.91mm2 and 1.63mm2 in turn.(5)The solidification heat transfer of 42CrMo steel during continuous casting was simulated by ProCAST software.The central temperature of billet surface,central temperature and solid-liquid isotherm showed regular changes under different superheat and casting speed conditions.In addition,with the increase of the distance from the meniscus,the central temperature of the slab surface decreases,which is consistent with the experimental law.(6)Using the CA-FE structure simulation module of ProCAST software to simulate the micro-structure of billet under different casting speed and superheat,the change rule was obtained.The results of tissue simulation were compared with the experimental results,and the simulated tissue growth was in good agreement with the experimental observations.