Effect of Pressure on Second Dendrite Arm Spacing and Columnar to Equiaxed Transition of 30Cr15Mo1N Ingot

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High‐nitrogen stainless bearing steel (HNSBS) is the most representative third‐generation aviation bearing steel, and the cleanliness and microstructure characteristics of bearing steel are crucial to its high performance and long service life. In this work, the effect of cerium addition on the cleanliness and microstructure characteristics of as‐cast HNSBS was systematically studied by combining microstructural characterization and thermodynamic analysis methods. The results show that with increasing Ce content, the cleanliness of steel first improved and then decreased, and Ce2O2S, Ce2O3 and CeN inclusions were generated successively. The Ce content should be controlled to ≈0.012 wt% to ensure that all Al2O3, MgO · Al2O3, and MnS inclusions were modified, and minimize the formation of large‐size Ce‐bearing inclusions. Furthermore, cerium addition refined the dendrite structure due to more nucleation sites for γ‐Fe and the enrichment of Ce in the liquid phase at solidifying front. The finer and more dispersed distribution in precipitates was ascribed to the reduction of growth space and Cr segregation, as well as the increase in effective nucleation sites. These results can offer theoretical guidance for inhibiting the formation of harmful inclusions in high‐nitrogen alloy systems and refining the microstructure of alloy systems containing M23(C, N)6 and M2(C, N) precipitates.

“…It has been reported that the secondary dendrite arm spacing in the HNSBS ingots is closely related to the cooling rate ( R ), which can be expressed as

log \left(\lambda\right)_{2} = 1.322 - 0.77 log R

Section: Resultsmentioning

confidence: 99%

Cerium Addition Improves Cleanliness and Refines Microstructure of As‐Cast High‐Nitrogen Stainless Bearing Steel

Lu,

Feng,

et al. 2023

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“…To obtain the nitrogen content during the solidification of 30Cr15Mo1N ingot, the cooling rate was simulated using ProCAST (ESI Group, Paris, FR) software, following the same methodology as our previous study. [8,10] The key solidification parameters and interfacial heat transfer are presented in Figure 4. However, due to the extensive nitrogen pore defects at different heights at 15 mm from the edge, it is difficult to count the SDAS.…”

Section: Nitrogen Content and Nitrogen Solubilitymentioning

confidence: 99%

“…As a result of the positive of nitrogen during the solidification of molten steel, the nitrogen content in the residual liquid phase along the interdendritic regions is considerably higher than the initial nitrogen content. [ 8,12,31 ] To calculate the nitrogen segregation in the 30Cr15Mo1N ingot, the Clyne–Kurz model is utilized. [ 32–34 ] The nitrogen content in the residual liquid phase can be determined using the following equation: [ 35 ]

$$\alpha = \frac{0.25 \left(\lambda\right)_{2} ^{2} V}{D \left(\right.

…”

Section: Theoretical Basis Of Bubble Nucleation and Growthmentioning

confidence: 99%

“…[1][2][3][4][5] In particular, in the case of 30Cr15Mo1N high-nitrogen steels (HNSs), nitrogen plays a crucial role in improving these properties. [6][7][8] However, the weak nitrogen retention capacity of 30Cr15Mo1N HNSs, which primarily consists of ferrite and martensite in its as-cast structure, leads to the escape of nitrogen from the molten steel during the smelting and solidification. [8][9][10][11] During solidification, the solubility of nitrogen changes due to phase transitions and nitrogen segregation, resulting in the nucleation of nitrogen bubbles in the residual liquid between dendrites.…”

Section: Introductionmentioning

confidence: 99%

“…[6][7][8] However, the weak nitrogen retention capacity of 30Cr15Mo1N HNSs, which primarily consists of ferrite and martensite in its as-cast structure, leads to the escape of nitrogen from the molten steel during the smelting and solidification. [8][9][10][11] During solidification, the solubility of nitrogen changes due to phase transitions and nitrogen segregation, resulting in the nucleation of nitrogen bubbles in the residual liquid between dendrites. [10,12,13] Some of the nitrogen bubbles are captured by the mushy zone during the rising process to form nitrogen pore defects in the 30Cr15Mo1N ingots.…”

Section: Introductionmentioning

confidence: 99%

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Revealing the Removal Mechanism of Vanadium Addition on Nitrogen Pores in 30Cr15Mo1N High‐Nitrogen Steel Ingot

Zhu,

Ni,

et al. 2023

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The removal mechanism of vanadium addition on nitrogen pores in 30Cr15Mo1N ingot is systematically investigated through statistical analysis and theoretical calculation. The nitrogen solubility is obtained by the thermodynamic model, and the nitrogen content is obtained by combining the ProCAST software and the C–K model. Then, according to the formula of critical nucleation radius and growth rate of nitrogen bubbles, the variation of critical nucleation radius and growth rate of nitrogen bubbles with different vanadium contents is calculated. As the vanadium content increases, the number and mean area of nitrogen pores decrease. In comparison to the 0 V ingot, the number of nitrogen pores decreases in the 0.2 V ingot, but there is an increase in the number of large‐sized nitrogen pores (>3000 μm in diameter). When the vanadium content increases to 0.4, the nitrogen pores are completely removed. The results demonstrate that increasing vanadium content can remove nitrogen pores. Since the solidification mode remains unchanged with increasing vanadium content, increasing the vanadium content cannot remove nitrogen pores by changing the solidification mode of the 30Cr15Mo1N ingots. Therefore, increasing the vanadium content removes the nitrogen pores mainly by inhibiting the nucleation of nitrogen bubbles and promoting nitrogen bubble overflow in 30Cr15Mo1N ingots.

Carbon Macrosegregation Pattern in 30Cr15Mo1N Ingot: Impact of Pouring Rate

He,

Zhu,

et al. 2024

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The effect of the pouring rate on the carbon macrosegregation in 30Cr15Mo1N ingots has been clarified by investigating changes in the content of carbon‐containing precipitated phases, cooling rate, secondary dendrite arm spacing (SDAS) and the flow characteristics of molten steel. During the solidification process, the solute‐enriched liquid steel migrates toward the center of the ingot under the action of convection, resulting in an increasing segregation ratio from the edge to the center. However, the growth of equiaxed grains partially restricts the flow of solute‐enriched liquid steel, which leads to a maximum segregation ratio not at the center but at approximately a quarter radius from the center. Furthermore, due to the upward flow of molten steel in the center, positive segregation occurs at the top. An increment in the pouring rate reduces the SDAS by enhancing the cooling rate, and thus the permeability decreases. It aggravates the carbon macrosegregation horizontally. However, increasing the pouring rate decreases the carbon macrosegregation vertically. This is due to the more intense flow of molten steel and the larger liquid phase region at higher pouring rate, which reduces the solute enrichment degree and promotes compositional homogeneity above and below the ingot.