Mechanical components for the automobiles, aircrafts and machines are required to have the higher strength, hardness and wear resistance, when these parts are generally subjected to high load and impact. Such mechanical properties can be obtained from the carburization and quenching processes. Thus,...
Mechanical components for the automobiles, aircrafts and machines are required to have the higher strength, hardness and wear resistance, when these parts are generally subjected to high load and impact. Such mechanical properties can be obtained from the carburization and quenching processes. Thus, numerical investigation using three-dimensional finite element program developed in this study was made to simulate the carburization and quenching processes. In order to simulate the carburization process, the second Fick's equation and carbon diffusional equation were adopted to describe the carbon diffusion in carbon steel. The carbon transfer coefficient was obtained from the experiment results. From the numerical investigation, it was found out that the carbon diffusion in the steel was activated well when the working temperature increased, while the carbon contents on the surface of steel decreased. Also, the numerically obtained carbon contents along the depth from the surface of the steel according to the time were in good agreement with experimental results available in the literature. For numerical simulation of the diffusional phase transformation such as austenite to ferrite and pearlite transformations occurred during the non-isothermal quenching process, subdivision of the cooling curve into various small isothermal steps was introduced with the help of various TTT diagrams of the carbon steel investigated. For this, Scheil's additive rule was adopted to predict the incubation time which indicates the onset of phase nucleation and also Johnson-Mehl-Avrami-Kolmogorov equation was used to model the phase growth. On the other hand, Koistinen and Marburger's empirical equation was used to model the diffusionless transformation from austenite to martensite transformation. Material properties depending on the temperature and carbon content available in references were used for more accurate simulations. Also, latent heat released due to phase transformation during the quenching was considered in this work. Through the FE investigation of the quenching process, the numerically obtained temperature history according to the time was in good agreement with the experiment results available in the literature for the cylindrical specimen with 0.79 wt. pct. C. Especially, the increase of the temperature due to latent-heat generation during the phase transformation was well simulated by the FE program developed in this work. Also, the temperature history for the hypoeutectoid steel and carburized carbon steel during the quenching was compared with that for the eutectoid steel. Finally, the phase distribution and generation procedure were analyzed for mechanical parts such as the bevel gear and cam lobe using the three-dimensional FE program developed. Due to the temperature variation and phase transformation, a dimensional change of the steel specimen takes place during the quenching process. Thus, in this study, a thermo-elastic-plastic constitutive equation was derived considering the thermal strain phase transformation strain, and transformation induced plasticity. Using the derived constitutive equation, thermo-elastic-plastic FE program was developed and used to predict the dimensional change and stress distribution according to the carbon content the change in temperature and volume fraction of each phase generated within the steel specimen. In order to validate the thermo-elastic-plastic program developed in this study, FE analyses of the quenching of the cylindrical eutectoid steel were carried out and it was found out that the numerically obtained values such as dimensional change and stress distribution were in good agreement with experimental results available in the literature. Also, FE simulations were also conducted to investigate the dimensional change of the hypoeutectoid steel since carbon content and the corresponding volume fraction of each phase generated is different compared to the eutectoid steel. Finally, the investigation on the dimensional change and stress distribution during the quenching of the shaft with key-hole groove and cam lobe was made as well. It was found out from this study that three-dimensional thermo-elastic-plastic FE program developed can be a useful tool in investigating the design parameters for the quenching process.
Mechanical components for the automobiles, aircrafts and machines are required to have the higher strength, hardness and wear resistance, when these parts are generally subjected to high load and impact. Such mechanical properties can be obtained from the carburization and quenching processes. Thus, numerical investigation using three-dimensional finite element program developed in this study was made to simulate the carburization and quenching processes. In order to simulate the carburization process, the second Fick's equation and carbon diffusional equation were adopted to describe the carbon diffusion in carbon steel. The carbon transfer coefficient was obtained from the experiment results. From the numerical investigation, it was found out that the carbon diffusion in the steel was activated well when the working temperature increased, while the carbon contents on the surface of steel decreased. Also, the numerically obtained carbon contents along the depth from the surface of the steel according to the time were in good agreement with experimental results available in the literature. For numerical simulation of the diffusional phase transformation such as austenite to ferrite and pearlite transformations occurred during the non-isothermal quenching process, subdivision of the cooling curve into various small isothermal steps was introduced with the help of various TTT diagrams of the carbon steel investigated. For this, Scheil's additive rule was adopted to predict the incubation time which indicates the onset of phase nucleation and also Johnson-Mehl-Avrami-Kolmogorov equation was used to model the phase growth. On the other hand, Koistinen and Marburger's empirical equation was used to model the diffusionless transformation from austenite to martensite transformation. Material properties depending on the temperature and carbon content available in references were used for more accurate simulations. Also, latent heat released due to phase transformation during the quenching was considered in this work. Through the FE investigation of the quenching process, the numerically obtained temperature history according to the time was in good agreement with the experiment results available in the literature for the cylindrical specimen with 0.79 wt. pct. C. Especially, the increase of the temperature due to latent-heat generation during the phase transformation was well simulated by the FE program developed in this work. Also, the temperature history for the hypoeutectoid steel and carburized carbon steel during the quenching was compared with that for the eutectoid steel. Finally, the phase distribution and generation procedure were analyzed for mechanical parts such as the bevel gear and cam lobe using the three-dimensional FE program developed. Due to the temperature variation and phase transformation, a dimensional change of the steel specimen takes place during the quenching process. Thus, in this study, a thermo-elastic-plastic constitutive equation was derived considering the thermal strain phase transformation strain, and transformation induced plasticity. Using the derived constitutive equation, thermo-elastic-plastic FE program was developed and used to predict the dimensional change and stress distribution according to the carbon content the change in temperature and volume fraction of each phase generated within the steel specimen. In order to validate the thermo-elastic-plastic program developed in this study, FE analyses of the quenching of the cylindrical eutectoid steel were carried out and it was found out that the numerically obtained values such as dimensional change and stress distribution were in good agreement with experimental results available in the literature. Also, FE simulations were also conducted to investigate the dimensional change of the hypoeutectoid steel since carbon content and the corresponding volume fraction of each phase generated is different compared to the eutectoid steel. Finally, the investigation on the dimensional change and stress distribution during the quenching of the shaft with key-hole groove and cam lobe was made as well. It was found out from this study that three-dimensional thermo-elastic-plastic FE program developed can be a useful tool in investigating the design parameters for the quenching process.
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