The Formation Mechanism of Mn–Al–O Inclusions in Fe–Cr–Mn Stainless Steel during Continuous Casting

Spring steel is extensively utilized in various sectors, such as automotive, engineering machinery, and electric power sectors, owing to its excellent elasticity. [1][2][3] The industries have stringent fatigue performances requirement for their products. [4] Inclusions are common sources of early fatigue faults, [5] which can cause premature spring fracture. For manufacturing highquality spring steel, a deep understanding of the formation and evolution of the inclusions in spring steel is essential.Si and Mn are commonly used as deoxidizers in high-quality spring steel. [6] Si-Mn-killed spring steel has inclusions with a low melting point, which deform more easily during rolling than the inclusions of Al-killed spring steel, thereby decreasing the damage of the inclusions on the fatigue life of the spring. [7] Al 2 O 3 and MgO-Al 2 O 3 inclusions with a high melting point can be formed with an excessively high Al content in steel. These inclusions can block the nozzle and shorten the fatigue life of spring. [8] Thus, alloys with a low Al content and refining slag are used to regulate the Al content in molten steel. [9][10][11] Inclusions form and evolve dynamically during continuous casting (CC) because of the continuous variations in the thermodynamic equilibrium between molten steel and inclusions in CC. According to Choudhary et al., [12] MnO-SiO 2 -Al 2 O 3 and Al 2 O 3 inclusions are formed during the solidification of Si-Mn-killed lowcarbon steel. They [13] further investigated the formation and evolution of the inclusions in low-carbon Al-killed steel during CC and predicted the types of precipitates with varying Mg contents. From their results, the Mg content in molten steel during ladle treatment should be kept below 0.8 ppm to prevent the formation of MgO•Al 2 O 3 spinel inclusions, which is consistent with the results of Ben. [14] Sonja et al. [15] observed an increase in the number of liquid inclusions in the steel and the formation of MnO-Al 2 O 3 spinel inclusions when the temperature dropped during the solidification of Si-Mn-killed steel. Goto et al. [16] investigated the influence of the initial oxides on the precipitation and growth of oxides during the solidification of Mn-killed steel. During solidification, the formation and growth of MnO-FeO oxides were independent of the initial oxide. Saburo et al. [17] discovered the relationship between the initial contents of Al and O in molten steel and changes in the Al 2 O 3 content in the MnO-SiO 2 -Al 2 O 3 inclusions during solidification. The inclusions were more stable during cooling with high initial amounts of Al and O. Zhong et al. [18] investigated the cooling process of silicon steel, whereby the precipitates were found to be mullite. The cooling rate had a significant impact on the precipitation and growth of the oxides. In particular, a slower cooling rate was beneficial for reducing the number of inclusions. Holappa et al. [19] investigated the evolution of the inclusions in Ca-treated Al-killed steels during solidification. They found ...

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Evolution Mechanism of MgO–Al₂O₃–SiO₂–CaO Inclusions During Continuous Casting of Si‐Killed Spring Steel

Wang

Wei

Zhang

et al. 2022

“…In this study, a lollipop sample well known to fully reflect the state of inclusions in molten steel [ 24,25 ] was taken in tundish. Three samples were taken at different positions of continuous casting slab to investigate the effect of cooling rate on AlN inclusions.…”

Section: Introductionmentioning

confidence: 99%

“…In this study, a lollipop sample well known to fully reflect the state of inclusions in molten steel [24,25] was taken in tundish.…”

Section: Introductionmentioning

confidence: 99%

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

Zhang

Chen

Cheng

et al. 2022

Self Cite

Industrial experiments are carried out to investigate the precipitation and growth of AlN in Fe–23Mn–2Al–0.08 V steel with nitrogen content up to 80–92 ppm. AlN inclusions can be precipitated before solidification. The morphologies of AlN are mainly divided into hexagonal and needle‐like shapes. With the cooling rate decreasing from 36.66 to 0.71 K s−1, the equivalent diameters of typical AlN increase from 7.56 to 24.20 μm, and the total amount decreases from 203.01 to 60.00 mm−2. The relationship between the cooling rate and the number density is obtained: lnNnormalV=29.848 + 0.453 lnRnormalC. The element segregation analyzed by electronic probe microanalyzer shows that aluminum concentration is low in interdendritic regions but high in dendrites. Aluminum segregation is very weak, and there is almost no nitrogen segregation. Thermodynamic calculation shows that AlN can precipitate before solidification with the nitrogen content higher than 58 ppm. The predicted results of AlN growth by kinetic analysis method can well reveal the growth trend. The nitrogen content (≥58 ppm) has a negligible effect on the size of AlN when the cooling rates are 3.02 and 0.71 K s−1, while the cooling rate has a significant effect on the size of AlN.

“…In addition, large inclusions would also be formed during casting process. The composition evolution, growth, and collision of non‐metallic inclusions during casting process have also attracted more and more attention . Choi et al investigated the evolution of oxide inclusions during solidification in 304 stainless steel slab .…”

Section: Introductionmentioning

confidence: 99%

Formation Mechanism of Large Inclusions in 80t 20Cr–8Ni Stainless Steel Casting for Nuclear Power

Wang

Cheng

et al. 2019

Self Cite

80t 20Cr-8Ni stainless steel castings are used to manufacture pump casing for nuclear power. However, large inclusions are usually observed on an ingot surface, which cause failure in penetrant testing. To clarify the formation mechanism of large inclusions, the evolution, growth, and aggregation of inclusions during the argon oxygen decarburization furnace (AOD) refining-Ca treatment-ingot casting process are investigated. The results show that Al 2 O 3 clusters >50 μm and single Al 2 O 3 particles >10 μm are typical large inclusions on ingot surface. After aluminum addition in AOD, typical inclusions are spinel or dual-phase CaO-MgO-Al 2 O 3 . After Ca treatment, typical inclusions are liquid or dual-phase CaO-MgO-Al 2 O 3 . With temperature decreasing during casting process, the mass fraction of Al 2 O 3 keeps on increasing due to decreasing oxygen and aluminum solubility. It is concluded that Al 2 O 3 is formed during casting process. Single Al 2 O 3 particles grow up to ≥7.5 μm or more. With the size of single Al 2 O 3 particles increasing, Al 2 O 3 clusters are formed mainly through Stokes and turbulent collision. In addition, the aggregation area of single Al 2 O 3 particles and Al 2 O 3 clusters is formed on the surface of ingot.