High Temperature Deformation Behavior And Oxidation Characteristics Of Cr18Mn18 High Nitrogen Steel

Cr18Mn18 high nitrogen steel has attracted wide attention due to its excellent corrosion resistance,high yield strength and good ductility and plasticity.However,due to its features of high flow stress,high dynamic recrystallization temperature and narrow hot processing temperature range under high temperature,it causes severe cracking during hot working such as hot forging,hot rolling and so on,resulting in a high rejection rate.Therefore,it is of great significance to further study high temperature deformation behavior and high temperature oxidation characteristics,to improve the hot-workability,to increase the hot-worked product yield and to promote the practical application of Cr18Mn18 high nitrogen steel.In this paper,Cr18Mn18 high nitrogen steel was prepared through being smelted under atmospheric pressure,the high temperature oxidation characteristics of which was studied,and focused on its high temperature deformation behavior.Based on which the constitutive model containing thermomechanical parameters and processing map were constructed,the hot forging optimization process was obtained through combining with the evolution law of microstructure.The results showed that as follows:Cr18Mn18 high nitrogen steel with nitrogen content of 0.85%was prepared through smelting at medium frequency induction furnace under atmospheric pressure.The change of alloying elements in ingot smelted through medium frequency induction furnace was not obvious after the electroslag remelting,the loss of Mn element was less than 2.6%,and the loss of N element was less than 2.4%.The chromium nitride and?phase disappeared obviously and microstructure was more uniform after the electroslag remelting.It could be seen from the tensile properties that the tensile strength and fracture elongation of samples prepared by electroslag remelting separately increased by 35%and 313%compared with that of the medium frequency induction furnace.Research on the high temperature oxidation characteristics of Cr18Mn18 high nitrogen steel showed that oxidation rate constant K_p at 950-1150?were K_P?950??=3.10×10^-5kg².m^-4.h^-1?K_P?1050??=1.85×10^-4kg².m^-4.h^-1?K_P?1150??=3.71×10^-4kg².m^-4.h^-1,respectively.The thermal activation energy Q of which was 191.40KJ/mol.The optimized thermal processing heating specification was that the temperature was higher than 1050?and the time was controlled within 6-8 hours,which was obtained through combining with the analysis of oxide layer composition and surface morphology of Cr18Mn18 high nitrogen steel.By studying the high temperature deformation behavior of Cr18Mn18 high nitrogen steel,building the constitutive model including the strain parameters and processing map,and combining with microstructure evolution law after hot compression,we could concluded that the dynamic recrystallization occurred at 1050?under the strain rate of0.1s^-1,the activation of dynamic recrystallization mechanism required the temperature need to reach 1100?at the strain rate of 0.5s^-1,and the entire experimental temperature range exhibited obvious work hardening features when the strain rate reached 1s^-1.The constitutive equations were constructed using the hyperbolic sine-type Arrhenius equation containing the strain parameters,through the comparison of the model predictions and experiments,good agreement was obtained in the entire strain range.Cr18Mn18 high nitrogen steel was forged using the optimized process,the properties and fracture morphology of the forged samples were analyzed.The results showed that the outer layer tensile strength of Cr18Mn18 high nitrogen steel after forging was obviously higher than that of the core layer,illustrating that the outer layer possessed more uniform plastic organization.The specimen showed no macroscopic cracks,and its average tensile strength reached 1140MPa,which increased by 83.0%and 35.1%,respectively,compared with the medium frequency induction furnace smelting and electroslag remelting.The average yield strength and elongation after fracture were 892.71MPa and 41.8%,which increased by 334.5%and 38.9%,respectively,compared with the medium frequency induction furnace smelting and electroslag remelting.