CONTINUOUSLY CAST P-MN BILLET HAVING SUPERIOR CRACK SENSITIVITY AND ELIMINATING SOAKING AND DIFFUSION HEAT TREATMENT

摘要

PURPOSE:To obtain the titled continuously cast billet by specifying the relasion between the space factor of a part having a specified concn. of above of segregated P in the total area of a sample having a restricted area taken out of the central part of a continuously cast billet and the number of segregated Mn grains having a specified minor axis size or above in said area. CONSTITUTION:A desired area 12 which is in a cross section of a continuously cast billet 10 in the lateral direction and includes the final solidification position 11 in the direction of the thickness is used as a sample. The area of the sample 12 is =0.04% of the cross-sectional area of the billet 10 in the lateral direction. The sample 12 is taken out and analyzed all over the surface. The space factor Ap(%) of a part contg. =0.1% P in the total area of the sample is plotted along the x-axis, and the number N' of segregated Mn grains having =1mm. minor axis size in the total area of the sample is plotted along the y-axis. At this time, the equation is satisfied.