Simulating Precipitation of Detrimental Boron Nitrides in Microalloyed Steels Based on Experimental Elemental Distributions

Abstract

Boron in solid solution increases considerably the hardenability of micro-alloyed steel. To control a complex microstructure and consequently the mechanical properties, a deep understanding of the distribution of elements and the limiting composition for boron nitride (BN) precipitation in steel is essential. In particular, heterogeneities in terms of local boron concentrations need to be evaluated. LA-ICP-MS revealed heterogeneous elemental distributions in the studied steel. Boron enrichment led to BN nucleation, closely related to TiN, as found by TEM analysis. This is reproduced by precipitation simulation, where BN nucleates in the boron enriched case only. Even though TiN is present in the simulation result, confirming experimental observation, its volume fraction seems not sufficiently high for complete N-binding and related “boron protection”. The present study reveals the great potential of determining threshold quantities of boron alloying for its complete solid solution by the coupling of quantitative element distribution analysis with thermokinetic simulation.