2002 Volume 88 Issue 3 Pages 142-147
The influence of thermal history on the surface hot-shortness of 0.3%Cu-0.05%Sn bearing steel was investigated in this paper. Surface hot-shortness was assessed by measuring the number of surface cracks occurring in the specimens which were held at 950 to 1200°C for 5 to 30 min after 1250°C heating in air, which were given 40% tensile-deformation at 1100°C in Ar gas atmosphere. The microstructure at the scale/steel interface was closely observed and the effect of Cu(Sn) on the surface hot-shortness was discussed.
Surface cracks occurred in the specimens which were held at 1200°C for 5 min and the number of surface cracks decreased in the specimens which were held for 10 to 30 min. At 1100°C, however, the number of surface cracks increased in the specimens which were held for 10 to 30 min. Cu(Sn) enriched alloy was observed at the scale/steel interface in the specimens where the number of surface cracks increased. In addition, Cu(Sn) concentrated film was observed at austenite grain boundaries.
The hot shortness is estimated to result from the liquid film of Cu(Sn) being precipitated at grain boundaries and its growth during cooling along with Fe-Cu phase diagram. The effect of holding temperature and time on the hot shortness was explained in terms of ξwhich was introduced as a parameter indicating the severity of cracking caused by Cu(Sn) enriched liquid film at grain boundaries.