The Research On Segregation Behavior Of Copper In Steel During Deformation Process

Through the thermodynamics calculation of solid solubility of copper in steel, the chemical free energy analysis of precipitation and the research on segregation at grain boundary, we get the law of copper equilibrium solid solubility with the changes of temperature in the α-Fe and γ-Fe and the thermodynamic basis of precipitation. Infer the rule of segregation and precipitation when the copper in steel deformed in high temperature, and study on the effect of copper content, deformation temperature, oxidation time and deformation rate on the surface crack of copper bearing steel. Obtain the relationship between the segregation of copper in steel and the surface crack and some effective measures to restrain the crack of copper bearing steel.The influence of different deformation on the crack is studied by using the copper bearing steel smelted in the laboratory. The results show that the formation of the crack on the surface of copper bearing steel has a critical value. When the deformation is less than 30%, no obvious cracks appear on the surface of the sample. With the increase of deformation, more cracks appear on the surface, but when the deformation reaches 50%, the crack increases slowly and tends to be saturated.Select the different copper content of ωCu=0.26% and ωCu=0.60%, at 1050℃, 1100℃, 1150℃, 1200℃, 1250℃temperature oxidation test, oxidation time is 10 min and 60 min, cooling way is divided into water cooling and cooling with the furnace. The results show that the higher copper content, the more serious the surface crack is. There is a certain critical temperature for the maximum crack in the steel with different copper content and the critical temperature is 1100℃-1150℃. The higher the heat treatment temperature, the less the surface crack. When the oxidation time is changed from 10 min to 60 min, the crack depth increases obviously. In the case of 60 min oxidation, the crack depth changes with the temperature is not obvious. Heating treatment at 1100-1250℃,there are copper precipitates in grain boundary and grain after quenching, and the concentration in grain boundary is higher than that in grain. With the furnace cooling, copper is mostly precipitated in the grain boundary, the iron substrate is almost no copper precipitates. Heating at 1050℃ and cooling with the furnace and cooling with the furnace, there are copper precipitates in the grain boundaries and inside.The results show that: in order to reduce the crack, we need to control the appropriate copper content, speed up the heating rate, fast through the 1100℃-1150℃, reduce the holding time and rapid cooling in the actual production.