EFFECTS OF COMBUSTION GAS IMPURITIES ON HIGH TEMPERATURE OXIDE SCALING OF STEEL

摘要

When carbon steel is reheated for hot working, it undergoes rapid scaling. The resulting yield losses are significant, at 1 to 2%. The present work was designed to investigate the effect of trace level sulfur impurities on the scaling rate. Samples of a low carbon steel, a high carbon high silicon spring steel and a high carbon intermediate silicon steel were exposed in the laboratory to simulated combustion gas corresponding to a 99% air to fuel ratio. In this gas, scaling rates were controlled by surface reactions, and linear kinetics resulted. Addition of 40ppm SO_2 to the gas changed the scaling rates for all steels: sulfur accelerated scaling at 1200℃, but slowed it at 1100℃. Similar effects were observed in the 99% gas with only 0.2ppm SO_2 additions. The results are interpreted in terms of adsorbed sulfur partially blocking surface reaction rates at 1100℃. The smaller extent of adsorption at 1200℃, and a suggested increase in surface mobilisation is thought to explain the faster scaling.