EXPERIMENTAL INVESTIGATION AND NUMERICAL SIMULATION OF CARBURIZATION LAYER EVOLUTION OF Cr25Ni35Nb AND Cr35Ni45Nb STEEL

Cr25Ni35Nb and Cr35Ni45Nb furnace tube steels, exposed to carbon-bearing environments at elevated temperature (1050-1150 degrees C), are susceptible to carburization attack, resulting in serious material deterioration and shortening service life. Depth of carburization layer, one of important marks of residual life for as-carburized furnace tubes, has been paid more attention frequently. In this paper, Depth growth of the carburization layer along the radial direction of Cr25Ni35Nb and Cr35Ni45Nb furnace tube was obtained by use of pack carburizing at two carburization temperature (1000 degrees C and 1100 degrees C) for different time. Then based on the Fick's second law and equilibrium constant method, a mathematical model for predicting variation of carburization layer of the two alloys above was established. The model consists of two parts: calculation of carbon diffusion based on Fick's second law and calculation of the carbide precipitation using equilibrium constant method. The results of numerical simulation are in agreement with the results of the experiments and the carburization time-dependent depth curve of carburization layer is parabolic.