The effects of process parameters on nitrogen infiltration and the controlling of nitrogen concentration in vacuum nitriding.

In vacuum nitriding, the effect of process parameters such as treating temperature and NH₃ concentration of infiltration gas to furnace on nitrogen concentration of specimen and the controlling of nitrogen concentration of the specimen are investigated. The decomposition of NH₃ in furnace is increased as the treating temperature is increased, therefore the nitrogen concentration of the specimen is decreased. The residual NH₃ concentration is increased as the treating temperature is decreased, therefore the infiltration nitrogen content to specimen is increased. If the residual NH₃ concentration is too high, the voids are generated and the nitrogen concentration decreases. The retention time in the furnace is decreased as the total gas flow rate is increased, therefore the residual NH₃ concentration increase and the nitrogen concentration increases. The number of NH₃ molecules per unit time, which contact on the steel surface can affect the infiltration amount of nitrogen. In other words, the infiltration nitrogen amount is according to the product of the residual NH₃ concentration by the exhaust gas flow rate.