Study On Grain Refinement Of 20Cr Steel During Thermoplastic Deformation Process

With the development of science and technology,all walks of life develop vigorously.Different industries have different requirements on the performance of steel materials.Iron and steel isdeveloping in the direction ofgiant and miniaturization with the idea of "clean purification,homogenization,fine crystallization".Using the method of physical or chemical can improve the performance of materials certain aspects,and fine grain strengtheningcurrently is one of the best strengthening mechanism can improve the strength of the materials at the same time,plastic toughness does not decrease or slightly reduced.With this technology,the cost of structural steel can be reduced,and even some alloy steels can be replaced.In this paper,the grain refinement behavior of 20 Cr steel during hot deformation is studied by theoretical analysis and experiment.The influence of some process parameters on grain refinement in the process of deformation is analyzed,and the mechanism of grain refinement is discussed.The thermodynamics and kinetics of deformation are analyzed.The reference is provided for the production of ultra-fine grained low carbon steel or low alloy steel in rolling production or forging parts.The main conclusions are as follows:(1)In the study of the effect of deformation temperature on the deformation induced ferrite transformation,it is found when the temperature exceeds the temperature range of the phase transition,the phase transition does not occur during compression;In the temperature range,the grain gradually thinning in the process of temperature reduction,when the temperature reaches a certain degree,and then reduce the temperature,the refining effect is not significant;The volume fraction of ferrite increases gradually.When the temperature reaches 750?,The volume fraction of ferrite decreased with the appearance of banded structure.(2)The occurrence of deformation induced by deformation requires some strain.After the transformation,the volume fraction of ferrite increases with the increase of strain,and the grain size increases slightly.(3)In low temperature,the small deformation rate leads to the formation of banded structure.With the increase of the deformation rate,the banded structure gradually disappeared,the amount of ferrite transformation increased,and the grainswere refined gradually.When the grain size is increased to a certain order,the deformation rate increases and the grain size is almost unchanged.(4)The microstructure of 20 Cr steel after different austenitizing temperature is different,but the difference is not significant.The grain size after phase transformation is almost not affected by the austenitizing temperature,but at low austenitizing temperature,the volume fraction of ferrite obtained by deformation is larger.(5)The mechanism of strain induced transformation of 20 Cr steel is the interaction of dynamic recrystallization and diffusion transformation.