MnS Precipitation Behavior of High-Sulfur Microalloyed Steel Under Sub-rapid Solidification Process

Abstract

A typical high-sulfur microalloyed steel was investigated by a sub-rapid solidification process for grain refinement of the as-cast microstructure. The size and distribution characteristics of the MnS precipitates were analyzed. The variations in the dendrite morphology and secondary dendrite arm spacing (SDAS) under different cooling rates have been studied, which strongly influence the precipitation behavior of MnS. The 3D-morphology of MnS precipitates was revealed by a novel saturated picric acid deep-etching method. Most MnS precipitates with a length smaller than 5 lm were columnar or equiaxed in the corresponding dendrite zones under sub-rapid solidification conditions at cooling rates of 261 to 2484 K/s. Furthermore, an area scan analysis of the precipitates showed the number of small MnS per square millimeter with lengths lower than 3 lm decrease from 200,537 to 110,067. The percentage of large MnS with a length over 5 lm increased from 2.6 to 6.2 pct as the solidification condition changed from sub-rapid to air cooling. In addition, the size of MnS precipitate was found to depend linearly on the SDAS.

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

“…Crystals tend to grow with facets, because this maximizes bond formation within a growth slice and therefore minimizes surface energy. [20,28] In addition, higher precipitation temperature and excessive precipitation amount of MnS in sulfur-containing steel are beneficial to the growth kinetics. As a result, more large-size MnS is observed in the sulfurcontaining 42CrMo steel due to the significant increasing of supersaturation during solidification and subsequent cooling process.…”

“…[6] Thus, regarding the important role of MnS inclusions in steel, lots of investigations have been performed, especially, the mechanism of morphology evolution by optimizing cooling rates. [15][16][17][18][19][20][21][22][23] At present, according to the classic work by Sims et al, the MnS in an as-cast steel can be typically classified as follows: globular MnS (Type I); fine rodlike MnS (Type II); and angular MnS (Type III). [15,16] However, the mechanisms of morphology evolution by various cooling rates still remain controversial.…”

Effect of Permanent Magnet Stirring on MnS Precipitation, Microstructure Evolution, and Mechanical Properties of High-Sulfur Micro-alloyed 49MnVS3 Steel

“…Enhancing the cooling rate and introducing physical fields are the two common methods for controlling the MnS precipitation of steel. [9][10][11][12][13] It has been reported that MnS precipitates in the as-cast steel should have a mean length lower than 5lm for to obtain better machinability and mechanical properties. [9] Wang et al [10] found that the percentage of the large MnS with a length over 5lm decreased from 6.2 to 2.6 pct as the solidification condition changed from air cooling to sub-rapid.…”

“…[9][10][11][12][13] It has been reported that MnS precipitates in the as-cast steel should have a mean length lower than 5lm for to obtain better machinability and mechanical properties. [9] Wang et al [10] found that the percentage of the large MnS with a length over 5lm decreased from 6.2 to 2.6 pct as the solidification condition changed from air cooling to sub-rapid. Zhang et al [5] revealed that electro-pulsing enabled the separation of MnS inclusions from molten steel according to the differences in electrical properties between the inclusions and liquid metal.…”