Effect Of Pre-deformation Process On Grain Refinement Of 100Cr6 Steel In SIMA

Strain Induced Melt Activation(SIMA)is an excellent semi-solid billets preparation method.It is not only suitable for semi-solid billets preparation of low melting alloy,but also suitable for high melting alloy.SIMA is usually divided into two stages: pre-deformation and semi-solid isothermal treatment(remelting),and the pre-deformation of grain refinement is the first step in the preparation of semi-solid billets by SIMA.In China,SIMA was widely used in the semi-solid billets preparation of low melting point alloys,such as aluminum alloy and magnesium alloy,but rarely used in the semi-solid billets preparation of high melting alloy,such as steel.Therefore,in the preparation of steel semi-solid billets by SIMA method,it is of great significance to study the effects of pre-deformation process on grain refinement in order to obtain fine non-dendritic billets.In this paper,100Cr6 steel was chosen as the research object,and the upsetting or the axial multi-pass upsetting and stretching was used as the pre-deformation process of SIMA.The effects of pre-deformation and the process parameters on grain refinement of 100Cr6 steel were studied by comparing the grain size of samples.The main researches and results are as follow:1.After the experimental schemes were designed with the appropriate pre-deformation process parameters,the upsetting tests of 100Cr6 steel were carried out on 400 kg air hammer and optical microscope etc.Then the effects of upsetting forging ratio on grain refinement of 100Cr6 steel were studied.The experimental results show that the average grain diameter decreases with the increase of upsetting forging ratio.2.Influences of the forging ratio or the upsetting and stretching passes on grain refinement of 100Cr6 steel were studied by axial multi-pass upsetting and stretching tests.It was found that with the increase of the forging ratio or the upsetting and stretching passes,the average diameter of the grains decreased rapidly first.When the forging ratio was over 1.67 or the upsetting and stretching passes was more than 2,the average grain diameter decreased slowly with the further increase of forging ratio or the upsetting and stretching passes,thus the effect of grain refinement was no longer significant.3.It was found that the axial multi-pass upsetting and stretching had better effect on grain refinement and homogenization than the upsetting by comparing the effects of these two kinds of pre-deformation processes on the grain refinement of 100Cr6 steel.So the axial multi-pass upsetting and stretching is a more suitable pre-deformation method,whose reasonable process parameters are forging ratio 2.0,upsetting and stretching passes of 3.Under these reasonable pre-deformation process parameters,the average diameter of the sample core grains decreased from 274.1μm to 25.0μm,a decrease of 90.9%,and the average diameter of the sample edge grains decreased from 293.4μm to 23.1μm,down 92.1%.The results show that the axial multi-pass upsetting and stretching is an excellent pre-deformation process of grain refinement in SIMA.4.The microstructure and hardness of the water-quenched samples after upsetting and stretching were studied and analyzed by scanning electron microscopy,energy dispersive spectrometer and hardness tester.The experimental results show that the microstructure of the water-quenched 100Cr6 steel specimens is quenched acicular martensite and a small amount of quenched lump troostite.The hardness of the water-quenched sample is between 59.3 HRC and 62.5 HRC,and changes slightly with the forging ratio or the upsetting and stretching passes.