Abstract:

Low carbon steels with B and P additions were remelted by electromagnetic levitation and solidified in a vacuum drop tube. The droplet volumes were set to be 2 mm × 2 mm × 2 mm (TM) and 5 mm × 5 mm × 5 mm (FM), respectively. The microstructure of rapidly solidified steel droplets (cooled in silicon oil) with P and both B and P addition was observed. The microstructures of B-bearing droplet samples were more uniform than those of B-free ones, for both TM and FM samples. The distribution of C and P along the diameter of each sample was detected. The well-distribution of C and P was detected in B-bearing droplet samples. So it could be deduced that B was also well distributed in the steels. It was B atoms that promoted the well-distribution of C and P, which further improved the uniformity of microstructure under the condition of rapid solidification. The micro-hardness of B-bearing samples was higher than that of B-free samples, and the hardening mechanism was discussed in detail.

Key words: Rapid solidification, Boron, Phosphorus, Droplet, Micro-hardness