Numerical Simulation of Full Carburizing Process of an Automotive Gear

The objective of the paper is to present material and numerical models needed to simulate with accuracy the full carburizing process of an automotive gear. The rough dimensions of the gear studied are 120mm in diameter and 45mm in height. From a numerical standpoint, as the carburizing affects only a thin layer under the surface, the mesh discretization must be adapted. Consequently, anisotropic mesh is used to describe accurately this zone. The temporal discretization must be also adapted to follow carbon diffusion and thermal evolution. The material models represent metallurgical phenomena during the complete carburizing process. The initial heating of the part induces phases transformation due to austenization. Subsequently, while holding at carburizing temperature, boundary conditions are applied to diffuse carbon into the part. While carbon content increases next to the surface, austenitic metallurgical grain growth is also modelled. A final cooling sets the properties of the carburized part. The model takes into account the phase changes using phase transformation diagrams locally adapted to chemical compositions and grain sizes. Simulation is used to predict the in-use properties of the gear at the end of the carburizing process as well as important results such as assessment of distortion and residual stresses. Thermal stresses, volume variation due to phase changes, and transformation plasticity all contribute to establish the final mechanical properties of the part. During the complete process, the material is modelled with an elasto-viscoplastic behavior and mixing methods are used to consider the relative contribution of each phase.

Modeling and Simulation of Vacuum Low Pressure Carburizing Process in Gear Steel

A combination of simulation and experimental approaches to optimize the vacuum carburizing process is necessary to replace the costly experimental trial-and-error method in time and resources. In order to accurately predict the microstructure evolution and mechanical properties of the vacuum carburizing process, a multi-field multi-scale coupled model considering the interaction of temperature, diffusion, phase transformation, and stress was established. Meanwhile, the improved model is combined with the heat treatment software COSMAP to realize the simulation of the low-pressure vacuum carburizing process. The low-pressure vacuum carburizing process of 20CrMo gear steel was simulated by COSMAP and compared with the experimental results to verify the model. The results indicated that the model could quantitatively obtain the carbon concentration distribution, Fe-C phase fraction, and hardness distribution. It can be found that the carbon content gradually decreased from the surface to the center. The surface carbon concentration is relatively high only after the carburizing stage. With the increase in diffusion time, the surface carbon concentration decreases, and the carburized layer depth increases. The simulated surface carbon concentration results and experimental results are in good agreement. However, there is an error between calculations and observations for the depth of the carburized layer. The error between simulation and experiment of the depth of carburized layer is less than 6%. The simulated surface hardness is 34 HV lower than the experimental surface hardness. The error of surface hardness is less than 5%, which indicates that the simulation results are reliable. Furthermore, vacuum carburizing processes with different diffusion times were simulated to achieve the carburizing target under specific requirements. The results demonstrated that the optimum process parameters are a carburizing time of 42 min and a diffusion time of 105 min. This provides reference and guidance for the development and optimization of the vacuum carburizing process.

Effects of Pre- and Post-Carburizing Surface Modification on the Tribological and Adhesion Properties of Heat-Resistant KHR 45A Steel for Cracking Tubes

In this study, the effects of ultrasonic nanocrystal surface modification (UNSM) technology on the tribological properties and scratch-induced adhesion behavior of a heat-resistant KHR 45A steel cracking tube, which is used for the pyrolysis process, were investigated. The main objective of this study is to investigate the effects of pre- and post-carburizing UNSM treatment on the tribological and adhesion performances of carburized domestic KHR 45A (A) steel and to compare the results with the existing carburized Kubota-made KHR 45A steel (B). A carburizing process was carried out on the polished and UNSM-treated KHR 45A steel substrates, which were cut out from the cracking tube, at 300 °C heat exposure for 300 h. The thickness of the carburizing layer was about 10 μm. UNSM technology was applied as pre- and post-carburizing surface treatment; both reduced the friction coefficient and wear rate compared to that of the carburized KHR 45A steel substrate. It was also found that the application of UNSM technology increased the critical load, which implies the improvement of adhesion behavior between the carburizing layer and the KHR steel substrate. The application of UNSM technology as pre- and post-carburizing surface treatment could help replace carburized Kubota-made KHR 45A steel (B) thanks to the improved tribological performance, enhanced scratch resistance, load bearing capacity, and adhesion of domestic KHR 45A (A) steel.

ANALISA PENGUATAN MATA PISAU MESIN PENCACAH SAMPAH ORGANIK DENGAN PROSES HEAT TREATMENT BERTINGKAT

Garbage has been considered useless and disgusting. The problem of pollution due to the presence of waste requires processing and management to overcome it, one of which is composting. The waste chopper is a tool that makes it easy to destroy and speed up the composting process of organic waste. The progress of the industrial sector cannot be separated from the development of the tool industry or blacksmiths, both large and small. In the manufacture of blades or blacksmith himself experienced several problems, among many consumers who complains of sharpness and strength of the blades are manufactured. There are several factors that affect the sharpness and strength of the blades, including during the heat treatment process. This study used an experimental method with ST 41 steel as the material. Carburizing process using coconut shell charcoal powder at a temperature of 875 ℃, hardness test and wear test material and the salt water quenching media. The highest average hardness test value was produced by the carburising and hardening processes with a hardness value of 599.7 VHN, while the lowest wear test value was found in the carburising and hardening process, namely 0,0000767 mm³ / kg.m.

Enhancement of Fatigue Life in St37 Steels by Carburizing Process

Carburizing is a heat treatment process, which used widely for surface hardening. In this process, the parts are placed in a concentrated atmosphere of Carbon atoms. The carbon atoms diffuse in the samples from the surface. In the present article, the effects of carburizing temperature on fatigue life will be studied. The St37 steel material is selected for study due to its wide range of usage in industry and little attention on the carburizing of this material. The samples are prepared by implementing the carburizing process at different temperatures (300, 400, 500, and 600 °C). The holding time is 1 hour for all samples. The two-point bending fatigue tests had been carried out on constant loading stresses. The results of the fatigue life test show that the fatigue life enhances the carburizing process. The fatigue life improved from about 45000 cycles to about 65000 cycles (about 44% increase) by increasing the temperature from 300°C to 600°C. Holding at higher temperatures leads to an increase in fatigue life smoothly due to the increase in the diffusivity coefficient. Also, the fracture surface demonstrates that the crack initiation starts from outer surfaces very slowly and failure happens as a brittle fracture in the samples.