Modeling of manganese sulfide formation during the solidification of steel

Journal of Materials Science, Oct 2016

A comprehensive model was developed to simulate manganese sulfide formation during the solidification of steel. This model coupled the formation kinetics of manganese sulfide with a microsegregation model linked to thermodynamic databases. Classical nucleation theory and a diffusion-controlled growth model were applied to describe the formation process. Particle size distribution (PSD) and particle-size-grouping (PSG) methods were used to model the size evolution. An adjustable parameter was introduced to consider collisions and was calibrated using the experimental results. With the determined parameters, the influences of the sulfur content and cooling rate on manganese sulfide formation were well predicted and in line with the experimental results. Combining the calculated and experimental results, it was found that with a decreasing cooling rate, the size distribution shifted entirely to larger values and the total inclusion number clearly decreased; however, with increasing sulfur content, the inclusion size increased, while the total inclusion number remained relatively constant.

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Modeling of manganese sulfide formation during the solidification of steel

Modeling of manganese sulfide formation during the solidification of steel Dali You 0 Susanne Katharina Michelic 0 Gerhard Wieser 0 Christian Bernhard 0 0 Montanuniversität Leoben , Franz-Josef-Straße 18, 8700 Leoben , Austria A comprehensive model was developed to simulate manganese sulfide formation during the solidification of steel. This model coupled the formation kinetics of manganese sulfide with a microsegregation model linked to thermodynamic databases. Classical nucleation theory and a diffusion-controlled growth model were applied to describe the formation process. Particle size distribution (PSD) and particle-size-grouping (PSG) methods were used to model the size evolution. An adjustable parameter was introduced to consider collisions and was calibrated using the experimental results. With the determined parameters, the influences of the sulfur content and cooling rate on manganese sulfide formation were well predicted and in line with the experimental results. Combining the calculated and experimental results, it was found that with a decreasing cooling rate, the size distribution shifted entirely to larger values and the total inclusion number clearly decreased; however, with increasing sulfur content, the inclusion size increased, while the total inclusion number remained relatively constant. - Non-metallic inclusions formed during solidification processes can essentially influence the final product quality. On the one hand, their presence can negatively affect steel properties [1–3]. On the other hand, they can contribute to a beneficial microstructure by acting as heterogeneous nucleation sites. To combine a preferably high steel cleanness with the creation of specific inclusion types and sizes for microstructure evolution, comprehensive knowledge of the inclusion formation is needed. A typical inclusion type that is formed in nearly every steel grade is manganese sulfide (MnS). The latter can lead to anisotropy of the steel matrix and act as a possible starting point for crack formation or corrosion [2, 3]. Apart from these negative effects, in the field of ‘Oxide Metallurgy’ [4, 5], MnS, whether as single-phase inclusion or together with titanium oxides, is known to act as a potential nucleation agent for the formation of acicular ferrite [6–8]. In addition, the formation of MnS prevents internal cracks resulting from the appearance of FeS and reduces hot tearing segregation [9]. Two factors have a significant impact on number density, size distribution, and total amount of formed MnS: the cooling rate and the sulfur content. Both parameters play an important role in process control and optimization, especially during casting, and can therefore directly affect the final product quality. Thus, it is not surprising that MnS formation has been extensively studied over the last several decades. Mathematical modeling provides a useful tool to investigate the formation of inclusions during the solidification of steel. Different researchers [10–13] developed several models describing MnS formation. MnS is normally generated from the enrichment of Mn and S in the residual liquid during the solidification process. Thus, it is important to consider the microsegregation of solutes when simulating MnS formation. Ueshima et al. [10] thermodynamically evaluated MnS formation based on an analysis of the interdendritic segregation. Imagumbai [11] applied a Solidification-Unit-Cell method to calculate the mean diameter of MnS, which depends on the cell volume, temperature gradient, and solidification speed. Valdez et al. [12] coupled Scheil’s model [14] and MnS growth to predict the size evolution. In their mean size prediction, Diederichs and Bleck [13] modified the empirical equation from Schwerdtfeger [15] into a function of manganese and sulfur contents, cooling rate, and secondary dendrite arm spacing. In this model, the concentrations of manganese and sulfur were calculated using the model of Clyne–Kurz [16]. In total, an enhanced model covering microsegregation, thermodynamics, and kinetics to describe the MnS size distribution has not been published thus far. The present paper proposes a comprehensive model of MnS formation during the solidification of steel. A deeper understanding of the nucleation and growth of manganese sulfide during the solidification of steels is desirable to reduce, control, and even benefit from the formation of MnS. For that purpose, the development of a comprehensive modeling approach for inclusion formation is continued. As a first step, a microsegregation model linked to thermodynamic databases has been developed [17, 18]. Second, coupled with the proposed microsegregation model, the thermodynamics of inclusion formation during the solidification process has been simulated [19]. In the present case, the modeling of inclusion formation is conducted by simultaneously considering the kinetics, microsegregation, and thermodynamics. Microsegregation is estimated (...truncated)


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Dali You, Susanne Katharina Michelic, Gerhard Wieser, Christian Bernhard. Modeling of manganese sulfide formation during the solidification of steel, Journal of Materials Science, 2017, pp. 1797-1812, Volume 52, Issue 3, DOI: 10.1007/s10853-016-0470-y