Understanding Partitioning and Segregation of Boron in Continuously Cast Slabs of 27MnB5 Steel

Trace addition of boron at approximate 40 ppm can have a significant effect on strength of steels. This research addresses B distribution in a continuously cast slab of 27MnB5 steel using nanoscale secondary ion mass spectrometry and atom probe tomography, to understand the segregation and partitioning of boron in main microstructural features of the steel. Unlike quenched plates, the slab develops boron enrichment in Ti(CN) precipitates, some cementite particles, or primary-austenite grain boundaries (PAGBs) depending on local cooling rate. The high-temperature Ti(CN) precipitates with partitioning of B implies that the precipitates should be taken into account for effective B addition in the steel. Partitioning of B atoms into cementite on/near the PAGBs in proeutectoid ferrite under slow cooling is responsible for desegregation of B at the PAGBs.