Influence of water vapor on surface hot-shortness of Cu-Sn containing steel

This paper describes the influence of water vapor on the surface hot-shortness of 0.3%Cu-0.05%Sn containing steel, mentioning the comparison of the hot-shortness in water vapor containing atmosphere to that in the air. Surface hot-shortness was assessed by measuring the number of surface cracks occurring in the hot-deformed specimens after 1250degreesC heating in x%H2O-1%O-2-bal.N-2, (x = 0, 10, 20, 30) atmosphere. The microstructure at the scale/steel interface was closely observed by optical microscopy and SEM. Structural analysis of scale was also made by X-ray diffraction and EPMA. The number of surface cracks increased with an increase in the water vapor content, and the width and depth of surface cracks increased as well. The hot shortness observed in specimens subjected to 20-30% water vapor occurred more severely than that for the specimens heated in the air, although the amount of scale for the former specimens is less than that for the latter. Discussion about the severe hot-shortness in water vapor containing atmosphere was given in terms of the flatness of scale/steel interface and Cu (Sn) enriched liquid alloys precipitated on Fe2SiO4 at the interface.