A method for predicting nitrogen gas pores in nitrogen alloying stainless steels

Yang, Seong-Ho; Lee, Zin-Hyoung

doi:10.1016/j.msea.2005.11.004

Cited by 16 publications

(17 citation statements)

References 18 publications

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“…5,6) However, the beneficial influence of nitrogen is usually limited by its low solubility in some steels, 3,4) which can result in serious nitrogen segregation and nitrogen pore defect during the melting and solidification of HNSs. Many thermodynamic studies 4,[7][8][9][10] suggested that increasing nitrogen partial pressure was able to enhance the solubility of nitrogen and effectively eliminate pore defects for a given HNS. Therefore, the pressurized metallurgy has been considered as a promising method to obtain melt with high nitrogen content and keep nitrogen dissolved during the solidification of HNSs.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Solidification Pressure on Interfacial Heat Transfer and Solidification Structure of 19Cr14Mn0.9N High Nitrogen Steel

Zhu

Wang

et al. 2018

ISIJ Int.

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The effect of solidification pressure (0.5, 0.85 and 1.2 MPa) on heat transfer between ingot and mould was investigated with the measurement of cooling curves and calculation of heat transfer coefficient. Combined with cooling rate, temperature gradient and local solidification time (LST), the influence of pressure on solidification structure of 19Cr14Mn0.9N was revealed by macrostructure observation. The calculation results of heat transfer coefficient, obtained by the Beck-Nonlinear estimation technique, indicate that increasing solidification pressure obviously enhances heat transfer at the ingot/mould interface. And higher solidification pressure is benefit to increase cooling rate and temperature gradient of ingot. Meanwhile, increasing solidification pressure considerably suppresses nitrogen gas pore, and reduces the whole area of dispersing porosity and shrinkage, which is favorable to obtain a sound ingot. With the solidification pressure increasing from 0.5 to 1.2 MPa, the columnar zone is lengthened, the columnar-toequiaxed transition (CET) position gradually moves to the ingot center, and both dendritic arm spacing (λ 1 and λ 2 ) and local solidification time (LST) gradually decrease. The solidification structure is significantly refined and compressed under higher solidification pressure.

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Section: Introductionmentioning

confidence: 99%

“…The shrinkage, porosity and pore, caused by supersaturation of gas (mainly nitrogen), have been some kinds of major problems in solidification structure of HNSs. 22,29) But there are scarcely any experimental studies on shrinkage, porosity and pore of HNSs manufactured by pressurized metallurgy.…”

Section: Introductionmentioning

confidence: 99%

Effect of Solidification Pressure on Interfacial Heat Transfer and Solidification Structure of 19Cr14Mn0.9N High Nitrogen Steel

Zhu

Wang

et al. 2018

ISIJ Int.

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“…This equation is usually used to quantitatively determine the critical nitrogen concentration N k or critical nitrogen pressure p k for pore formation [4,5]. However, for several reasons, Eq.…”

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confidence: 99%

“…Several studies [4][5][6][7] have been devoted to determining the critical nitrogen concentration N k or critical nitrogen pressure p k for bubble formation. For example, the Thermo-Calc program was used in [4] to calculate the average composition of the liquid phase during the solidification of stainless steel and the corresponding equilibrium nitrogen pressure.…”

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Critical Nitrogen Concentration in High-Nitrogen Steels for the Production of a Dense Ingot

et al. 2015

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The critical concentration of nitrogen in steel during its equilibrium crystallization is best defined as the concentration at which the nitrogen content of the remaining liquid steel does not exceed nitrogen's solubility in the liquid at the given pressure and temperature. The critical nitrogen concentration is most expediently determined by means of the program Thermo-Calc. Calculated values of critical concentration obtained from the program should then be refined in practice for specific crystallization conditions.Nitrogen is a gaseous alloying element. The solubility of nitrogen is appreciably different in the liquid metal and the α and γ phases. Thus, among the technological problems encountered in alloying liquid steel with nitrogen are the formation of gaseous nitrogen during solidification of the melt, the formation of nitrogen bubbles, and the formation of pores in the cast ingot. The nitrogen content of the steel needs to be increased in order to obtain an ingot having the required structure and properties, but it also needs to be decreased in order to form a dense ingot. This situation has kept the potential of nitrogen from being fully realized as an alloying element in steel. Despite the wide use of steels alloyed with nitrogen, no solution has yet been found to the problem of predicting the critical concentration of nitrogen in Cr-Ni-Mn steels -the concentration above which bubbles and pores are formed in the steels. During solidification, the compositions of the liquid phase and the still-forming solid phases change continuously in relation to the temperature and amount of the remaining liquid phase. In addition, the local solubility of nitrogen in the liquid phase changes in relation to the type of crystallization (austenitic, ferritic, or mixed) and the proportions of the phases. Thus, the critical concentration of nitrogen is specific to the composition of the steel that is being made.The studies [1-3] examined the formation of bubbles during the solidification of pure iron and steels Cr18Ni10 and C0.13Cr13 having different contents of surface-active elements (surfactants), oxygen, and sulfur. It was established that the formation of nitrogen bubbles during solidification depends on the degree of saturation of the steel with nitrogen, the content of surfactants in the steel, total gas pressure in the system during solidification, and the rate of cooling of the melt. However, together with the degree of supersaturation, the factor that most heavily affects nitrogen bubble formation is the steel's content of surfactants. Thus, the quantity of bubbles in the ingot is determined not by the rate of formation of gas-phase nuclei but by the rate at which gaseous nitrogen is formed in existing nuclei, i.e., by the bubbles' rate of growth. Bubble growth rate in turn depends heavily on surfactant content and temperature. When the rate of formation of gaseous nitrogen is low,

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Effect of Solidification Pressure on Compactness Degree of 19Cr14Mn0.9N High Nitrogen Steel Using CAFE Method

Zhu

et al. 2017

steel research int.

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The cellular automaton‐finite element (CAFE) model is used to simulate solidification structures of 19Cr14Mn0.9N high nitrogen steel under different solidification pressures. The effect of solidification pressure on model parameters is firstly investigated. After validation, this model is used to clarify the effect of solidification pressure on compactness degree with number of grains and primary dendrite arm spacing (λ1). The results show that increasing solidification pressure from 0.5 to 1.2 MPa exhibits a significant increment (200 W m2 K−1)) on heat transfer coefficient and slight change for other model parameters. The model validation indicates CAFE model can accurately simulate solidification structure under higher solidification pressure. Under higher solidification pressure, the primary dendrite arm spacing (λ1) of central equiaxed grain becomes smaller and the number of grains of the whole ingot increases obviously, revealing a further improvement on the compactness degree of ingot. At a given pressure, the decrement in the number of grains is obvious away from the edge of ingot. With increasing solidification pressure, a more significant increment in the number of grains exists at columnar grain zone than that at central equiaxed grain zone, suggesting a greater increasing tendency of compactness degree at columnar grain zone.

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A method for predicting nitrogen gas pores in nitrogen alloying stainless steels

Cited by 16 publications

References 18 publications

Effect of Solidification Pressure on Interfacial Heat Transfer and Solidification Structure of 19Cr14Mn0.9N High Nitrogen Steel

Effect of Solidification Pressure on Interfacial Heat Transfer and Solidification Structure of 19Cr14Mn0.9N High Nitrogen Steel

Critical Nitrogen Concentration in High-Nitrogen Steels for the Production of a Dense Ingot

Effect of Solidification Pressure on Compactness Degree of 19Cr14Mn0.9N High Nitrogen Steel Using CAFE Method

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