Nucleation, Growth, Sintering, and Densification of Sulfide in 1215MS Free‐Cutting Steel Billet

Abstract

Herein, the nucleation, growth, aggregation, sintering, and densification of sulfide in 1215MS free-cutting steel billet with a total oxygen concentration of 70 ppm are investigated. A portion of oxygen in the steel dissolves in sulfide to form oxysulfide, Mn(S,O), which can be single-particle spherelike (SPS), doubleparticle rodlike (DPR), and multi-particle rodlike (MPR), and SiO 2 can precipitate at the outer edge of the SPS and connection in the DPR and MPR inclusion particles to form Mn(S,O)-SiO 2 inclusion, which is formed by the change of liquid inclusion, that undergoes monotectic reaction to form oxides and oxysulfide. The possible phase-transition process can be expressed as (Mn,Si) x (S, O) y (l) ! Mn(S,O)(l ! s) þ (Mn,Si) x O y (s) ! Mn(S,O)(s) þ SiO 2 (s). Oxysulfide inclusions can aggregate under the influence of van der Waals and viscous drag forces. The larger the particle, the greater the critical spacing and aggregation force. MPR oxysulfide can be divided into three parts: droplet, flat surface, and neck, which have decreasing chemical potentials in turn. Sintering and densification occur after the aggregation of particles, where surface diffusion of elements dominates, while grain boundary diffusion and bulk diffusion dominate in the densification of particles. Meanwhile, the formation and evolution of five different morphologies of sulfides in 1215MS free-cutting steels are discussed.

The Effect of Alloying Elements on Formation and Evolution Mechanism of Manganese‐Containing Inclusions in Medium/High‐Manganese Steels

“…Simultaneously, confirming the promoting effect of alloy elements on the growth of MnS, which is consistent with the results reported in previous publication. [ 34 ] In contrast, through the values of increase in element concentration and the corresponding decrease in solid phase fraction, it can be found that C element is more effective in promoting the precipitation of MnS, followed by Si and Mn elements. This phenomenon may be attributed to the high sensitivity of C element on changes in the liquid‐solid phase zone, which affects the distribution coefficient of solutes during solidification, leading to early precipitation of MnS.…”

“…From the above analysis results, it found that the manganese‐containing inclusions in MMC10, MHC10, and MS10 steel are mainly large irregular MnS inclusions, which can be considered that Type III of MnS is caused by boosting divorced eutectic transformation under the action of C and Si elements. [ 34 ]…”

“…From the above analysis results, it found that the manganese-containing inclusions in MMC10, MHC10, and MS10 steel are mainly large irregular MnS inclusions, which can be considered that Type III of MnS is caused by boosting divorced eutectic transformation under the action of C and Si elements. [34] Similarly, the elemental mapping of a typical manganesecontaining inclusion in MMC10, MHC10, and MS10 steel is shown in Figure 9. In MnS-TiN inclusion of MMC10 steel, the distribution of Ti and N element located in the outer layer of the inclusions (Figure 9a).…”

Ductile Fracture Behavior of ASTM A516 Gr.70 Pressure Vessel Steel by ASTM and ISO Fracture Toughness Standards

“…Manganese Sulphide (MnS) inclusions were observed in the steel through optical microscopy as finely dispersed particles with globular morphology, as presented in Figure 4. These inclusions are classified as type I and are formed when oxygen and sulfur solubilities are high and low, respectively [37][38][39][40].…”