Effects of cooling rate and Al on MnS formation in medium-carbon non-quenched and tempered steels

Abstract

Abstract:The effect of Al on the morphology of MnS in medium-carbon non-quenched and tempered steel was investigated at three different cooling rates of 0.24, 0.43, and 200°C⋅s. The formation mechanisms of three types of MnS were elucidated based on phase diagram information combined with crystal growth models. The morphology of MnS is governed by the precipitation mode and the growth conditions. A monotectic reaction and subsequent fast solidification lead to globular Type I MnS. Type II MnS inclusions with different morphological characteristics form as a result of a eutectic reaction followed by the growth in the Fe matrix. Type III MnS presents a divorced eutectic morphology. At the cooling rate of 0.24°C·s , the formation of Type I and Type II MnS inclusions is promoted, and the influence of Al is negligible. The results of this work are expected to be employed in practice to improve the mechanical properties of non-quenched and tempered steels.

Effect of Manganese on the Formation Mechanism of Nonmetallic Inclusions in Fe–xMn–7Al–0.7C Lightweight Steel

“…The increase of Mn content significantly reduces the liquidus temperature of the steel, resulting in the precipitation of MnS in the early stage of solidification, and the morphology of the primary precipitation of MnS is considered to be polyhedral. [36] Likewise, the composition and cooling rate of the steel in this experiment are consistent with the conditions for the precipitation of polyhedral MnS inclusions in the Fe-MnS pseudo-phase portrait. [37]…”

Morphology of Solidification Structure and MnS Inclusion in High Carbon Steel Continuously Cast Bloom

“…Also the calcium treatment 16,17) and Rare-Earth-Metals (REM) treatment 18) are popular ways to modify sulfides in the molten steel before casting and obtain a homogeneous distribution of precipitated sulfides in the solidified steel. Moreover, high cooling intensity 19,20) is benefit for the formation of globular Type I MnS in steel during the solidification process through metastable monotectic reaction due to small temperature difference between the eutectic point and the monotectic point. Shape change of MnS inclusion from the Type II and III to Type I can also be accomplished by heat treatments 21,22) and finally the complete spheroidization of the MnS inclusions is obtained in the steel.…”

Formation of Complex Inclusions in Gear Steels for Modification of Manganese Sulphide

“…Most of the oxide and sulphide inclusions are endogenous, formed as the result of deoxidation of steel. However, dual phase types with or without sulphides and pure sulphide inclusions are generated during all succeeding stages of steel processing, even during solidification [1,[6][7][8][9][10]. In contrast, alumina (Al 2 O 3 ) is another type of inclusion generated as the result of Al deoxidation in molten steel.…”