Effect of Nitrogen Content on the Formation of Inclusions in Fe-5Mn-3Al Steels

Abstract

The effect of N content on the characteristics and formation of inclusions in the Fe-5Mn-3Al steels was investigated in this study. Two synthetic steel melts were produced by two different methods—N2 gas purging and injecting—to introduce nitrogen into the melt. The N content of steel melt varied from 2 to 54 ppm. An increase in the N content to 47 ppm (for 533N-P) and 58 ppm (for 533N-I) increased the total amount of inclusions from 13 to 64 mm−2 and from 21 to 101 mm−2, respectively. The observed inclusions were Al2O3(pure), Al2O3-MnS, AlN(pure), AlN-MnS, AlON, AlON-MnS, and MnS. When the N content was less than 10 ppm, AlN-MnS inclusions were the primary type of inclusions and they formed as solidification products. With an increase in the N content, AlN(pure) inclusions became the dominant type of inclusions as AlN was stable in the liquid steel. These findings were confirmed by thermodynamic calculations. The influence of cooling rate on the types of inclusions was studied and a higher number of AlN-MnS inclusions were observed in samples with slow cooling rate.

Effects of Nitrogen on the Microstructure and Mechanical Properties of Fe–28Mn–10Al–0.8C Low‐Density Steel

“…It is well known that dispersive and fine second‐phase particles refine the grains in steel. [ 11,14–25 ] As previously mentioned, the number of inclusions smaller than 2 μm in the HN steel was significantly greater than that in the LN steel, and AlN inclusions were formed during the smelting process for the HN steel. The fine AlN inclusions acted as the cores of the heterogeneous nucleation of austenite during the solidification process.…”

“…In general, AlN inclusions are generated during the solidification process with lower Al and N contents and can be formed in molten steel with higher Al and N contents. Alba et al [ 20 ] concluded that the main inclusion was AlN–MnS inclusion in Fe–5Mn–3Al steel, whereas the nitrogen content was less than 10 ppm. With an increase in N content, AlN became the dominant inclusion.…”

“…Lu et al [ 19 ] reported that AlN inclusions form in liquidus steel when the contents of Al and N exceed the critical solubility of AlN inclusions in high‐nitrogen stainless bearing steel. Alba et al [ 20 ] reported that AlN was the dominant inclusion, and the total number of inclusions increased with an increase in the nitrogen content in Fe–5Mn–3Al steel. Park et al [ 21 ] reported that both AlN and AlON inclusions increased with increasing Al content in Fe–Mn–Al steel.…”

Influence of Al and N Content and Cooling Rate on the Characteristics of Complex MnS Inclusions in AHSS

“…Whereas a small portion of MnS is located between Al 2 O 3 and AlN phases in AlON-MnS inclusions (Figure 1c). Detailed inclusion analyses of the current experiments are presented and discussed elsewhere [19,20]. Figure 2 presents the number per unit area (N A ) of complex MnS inclusions observed in the air cooled samples of all experimental steels.…”

Effect of Cooling Rate and High N Content on the Precipitation and Growth of AlN Inclusions in Fe–23Mn–2Al–0.08 V High‐Manganese Nonmagnetic Steel

“…The precipitation and growth of inclusions are closely related to the composition of liquid steel, microsegregation of elements, and cooling rate during solidification. [ 4,6,9–15 ] It is well known that AlN inclusions precipitate during solidification of regular Al‐killed steels containing 0.04–0.05 mass% aluminum. [ 9,16 ] Many researchers [ 9,17 ] have found that AlN could precipitate before solidification of high‐aluminum and high‐nitrogen steel.…”