Abstract
Controlling the formation of MnS inclusions during solidification influences the mechanical properties and machinability of the resulfurized steel. A coupled segregation–nucleation–growth model was developed by the finite-difference method involving solute redistribution, heterogeneous nucleation and growth kinetics. Laboratory solidification experiments were performed under various cooling rates in resulphurised 49MnVS steel. In this work, the influence of cooling rate on solute redistribution and growth size of MnS inclusions were simulated using the current coupled model, and the calculated results can provide a valuable reference for MnS formation. Increasing of the cooling rate led to early precipitation and refinement of formed MnS inclusions. Based on the simulation results and experimental data, mathematical relationships between the growing size of MnS with the cooling rate in the low ductility temperature region and in the whole solidification were obtained.
Highlights
Over the past few decades, MnS inclusions have been considered as detrimental species in steel matrix, and many effects have been made for desulfurization in the processes of hot metal pretreatment and converter steelmaking, etc [1]
Whereas, N0 is the number of nodes in the dislocation network, Z is the Zeldovich constant (0.05), β’ is the atomic impingement rate, kb is the Boltzmann constant (1.38065 × 10−23 J/K), τ is the incubation time, the precipitation of MnS on dislocations is assumed to be instantaneous and the incubation time is considered to be zero, t is growth time, ρ is the dislocation density, which is about 1013 m−2 in low carbon steel, Cdi and Ddi represent the concentration and diffusion coefficient of the rate determining elements, in the MnS formation system the determining species is Mn or S, and a0 is the lattice parameter
Ni · Cδ,i δ/γ where TFe and TFe are the melting temperature of pure iron (1536 ◦ C) and the δ/γ transformation temperature of pure iron (1392 ◦ C), mi and ni are the slopes of liquidus and Ar4 line according to the pseudobinary Fe-phase diagram, CL,i and Cδ,i are the solute concentration of element i in liquid and solid phase
Summary
Over the past few decades, MnS inclusions have been considered as detrimental species in steel matrix, and many effects have been made for desulfurization in the processes of hot metal pretreatment and converter steelmaking, etc [1]. The comprehensive understanding and control of precipitation and growth of MnS inclusions during solidification are essential. MnS is normally precipitated in the enriched remnant liquid during solidification and many models have been proposed to analyze the precipitation of MnS inclusions based on the redistribution of solute elements [9]. A comprehensive model encompassing microsegregation, cellular automatonand andkinetics demonstrated that the and formation of MnS accomplishedand by dendrite growth. The present a newand coupled model of MnS inclusions precipitation and growth during. A new coupled model of inclusions precipitation and growth during solidification was proposed based on previous work [19,20]. Using the current coupled model, the solidification was proposed based on previous work [19,20].
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