Precipitation Characteristic of Sulfide in Medium‐Carbon Sulfur‐Containing Steel

Abstract

Herein, the precipitation characteristic of sulfide is investigated by confocal laser scanning microscopy for a typical medium‐carbon sulfur‐containing 42CrMo steel under different cooling rates (100, 200, 600 °C min−1) and sulfur contents (0.0018 and 0.0249 wt%). Thermodynamic calculations show that increasing sulfur content can enlarge the liquid–solid‐phase zone and enhance the initial precipitation temperature of MnS in 42CrMo steel. Phase diagram of Mn–Mo–S demonstrates that the sulfides contain Mn, Mo, and S elements can be formed. The experimental results indicate that with an increase of the sulfur content from 0.0018 to 0.0249 wt%, more (Mn, Mo)S sulfides are formed in the steel due to the significant enhancement of supersaturation. Moreover, it is revealed that the average size of (Mn, Mo)S inclusions decreases from 16.11 to 3.55 μm when the cooling rate increases from 100 to 600 °C min−1. The typical of large‐size rodlike (Mn, Mo)S inclusions is observed in a low cooling rates of 100–200 °C min−1. As the cooling rate increases to 600 °C min−1, smaller globular (Mn, Mo)S inclusions with an average size of 3.55 μm are appeared which can act as a core to promote the ferrite formation.

Effect of Flow Rate and Partial Pressure of Oxygen on Desulfurization of KR Slag

“…This phenomenon occurred because Ca 2+ and S 2− ions in KR desulfurization slag exhibit low electrostatic potentials at low oxygen pressures (P O 2 < 0.20 bar), resulting in the formation of CaS ion pairs. This is in line with the findings of He H Y et al's [22] investigation on the mechanism of sulfur occurrence in LF refining slag, which discovered that the majority of the sulfur in the slag is present as CaS. Under high oxygen pressure (P O 2 ≥ 0.20 bar), due to the high concentration of oxygen in the oxidation system, the O 2− activity in KR desulfurization slag is higher and combines with Ca 2+ in the slag to form CaO.…”