Transverse facial cracks occurring in boron-containing CC slabs were fractographically analysed and the cause was found to be austenite grain boundary fracture due to the precipitation of BN along it. The embrittlement due to BN precipitation was very well simulated by the hot tensile test with Gleeble Tester.
In order to avoid the facial cracks, two methods were proposed. One is the reduction of nitrogen content to satisfy the condition; (wt% Nt-0.2×wt%Ti)<0.003 wt%, and the other is the keeping of cooling rate less than 0.5°C/s in the secondary cooling zone to promote matrix precipitation of coarse BN.
