1988 Volume 74 Issue 7 Pages 1290-1297
Surface crack which occurs in unbending process during continuous casting, was investigated by hot tensile test mainly at 750°C in relation to Nb, V carbo-nitride and proeutectoid ferrite in Nb, V containing steels.
Amount of dynamically precipitating carbo-nitride has close relation to the value of load integration which was newly introduced parameter.
Surface crack sensitivity grows higher as the parameter becomes larger because more Nb, V carbo-nitrides precipitate at grain boundary and intercrystalline, which leads to the increase of total amount of precipitates.
Thin Proeutectoid Ferrite around austenite grain boundaries was observed when deformation was introduced at 750°C, and the ferrite also increased crack sensitivity.
To avoid surface cracks in continuous casting, reducing the number and zone length of unbending points is effective because load integration value decreases. Furthermore, surface crack sensitivity can also be improved when the temperature at unbending is higher than 950°C because the amount of Nb, V carbo-nitride becomes less and ferrite precipitation does not occur.
