(286f) Cfd Modeling of Acetylene Pyrolysis for Low Pressure Carburizing of Steel

The vacuum carburizing or low pressure carburizing of steel is a modern process for the case hardening of steel parts such as gearbox parts or shafts that need a wear resistant, hard surface with a co-requisite ductile core. The process, as its name implies, is carried out in a vacuum furnace at pressures below normal atmospheric pressure. Vacuum carburizing process demands the uniformity and repeatability required to meet the quality specifications for precision parts. The formation of soot and higher hydrocarbons which can settle on furnace walls are critical problems which need to be addressed. To overcome these problems, propane (C3H8), ethylene (C2H4) or acetylene (C2H2) are being used for carburizing at pressures below 20 mbar. The steel parts are exposed to the carburizing gas at temperatures between 900-1050 °C and total pressures between 2-20 mbar. Under the high temperature the carburizing gases are pyrolyzed and form atomic carbon on the steel surface. The carbon diffuses into the steel and locally increases the carbon concentration. The amount of carbon available for carburizing the steel depends on the process parameters such as partial pressure of the carburizing gas, carbon content in the carburizing gas and the pyrolysis reactions of the carburizing gas. The pyrolysis reactions of the carburizing gas are also affected by the contacting pattern or how the gas flows through and contacts with the steel parts being carburized. The objective of this research is the development of a computational fluid dynamics model for the numerical simulation of homogeneous pyrolysis of acetylene under vacuum carburizing conditions of steel.