Effect of Sulfur Content on the Inclusion and Mechanical Properties in Ce-Mg Treated Resulfurized SCr420H Steel

Abstract

To clarify the effect of sulfur on inclusions and mechanical properties of Ce-Mg treated resulfurized SCr420H steel. Laboratory experiments were conducted to prepare steels with sulfur contents as 0.01%, 0.06%, and 0.132%. Inclusion evolution in liquid steel, MnS precipitation during solidification, and tensile test results of steel after quenching and tempering were investigated. The results showed that due to the limitation of mass transfer in molten steel, composite inclusion that Ce-O-S wrapped by Ce-Ca-Mg-Al-Si-O, which was named transition state inclusions, can form quickly after adding Ce-Mg lump to the molten steel. As the homogenization of molten steel, the difference of sulfur content in steel can lead to the transition state inclusions transformed into different inclusions. With the increase of sulfur content, the quantity of MnS increased significantly, and the morphology of MnS transformed from “stick” to “dendritic + fishbone”, and then to “fishbone”. Tensile test results and fracture analysis indicate that the decline of inclusion spacing as the increase of sulfur content leads to a shorter physical path of crack propagation in steel. Therefore, the increase of sulfur content can bring about a decrease in the strength and plasticity of the steel. From the perspective of inclusion control, making the MnS inclusion precipitate more dispersive and increasing the distance between inclusions can be considered as a method for preventing the decline of mechanical properties in steel with high sulfur content.

Cause Analysis of Low Tensile Plasticity in Normal Direction for Hot‐Rolled Thick Plate of HSLA Steel

“…The factors that could reduce the tensile plasticity in ND of a thick plate were the central shrinkage cavity that was not rolled together, [7,8] internal cracks, [9,10] and largesized inclusions. [11][12][13][14][15] The central shrinkage cavity that was not rolled together was mainly found in the extra-thick plates with small deformation in rolling process. [7] The continuous casting slab which was used for the production of extra-thick plate was also thicker.…”

Effect of La Content on Inclusion Morphology in Automobile Sulfur‐Containing Gear Steel SCr420H

“…MnS inclusions in steel have a vital effect on the machinability, owing to the lubrication of effect. [1][2][3][4][5][6][7][8][9][10] A steel plant in China considered enhancing the machinability of steel SCr420H by increasing the S content in gear steel and forming a large number of MnS in steel. However, MnS inclusion tends to aggregate in clusters distributed in steel billet and elongate in the rolling direction after hot rolling, which is detrimental to the anisotropy of the mechanical properties of steel.…”

“…However, MnS inclusion tends to aggregate in clusters distributed in steel billet and elongate in the rolling direction after hot rolling, which is detrimental to the anisotropy of the mechanical properties of steel. [4,11,12] Thus, the morphology control of sulfide is one of the crucial issues for producing automobile sulfur-containing steel.Some control methods with very excellent performance have been proposed for sulfide morphology control, such as Mg treatment, [6,13] Te treatment, [5,14,15] and Ca treatment, [16] but these control methods have some drawbacks. The solubility of Mg and Ca in steel is very low, and the content of Mg and Ca in steel is generally reported to be below 100 ppm.…”

“…However, MnS inclusion tends to aggregate in clusters distributed in steel billet and elongate in the rolling direction after hot rolling, which is detrimental to the anisotropy of the mechanical properties of steel. [4,11,12] Thus, the morphology control of sulfide is one of the crucial issues for producing automobile sulfur-containing steel.…”