Effect of Solidification Pressure on Phase Transformation and Precipitated Phases of 30Cr15Mo1N Ingot

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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.

Section: Introductionmentioning

confidence: 99%

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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Evolution of Temperature Field of Slabs during the Feeding Strip Process in Continuous Casting

Zhu

Zhang

et al. 2023

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The implementation of a feeding strip is a widely recognized and effective technique to improve the quality of continuous cast slabs. To comprehensively understand the effect of feeding strip on the temperature field of slabs during continuous casting, a mathematical model is developed that considers the breaking and shedding of strip, and, the accuracy of the developed model is verified by the macroscopic structural observations of S32654 steel ingot. During the feeding strip process, changes in the morphology of strip undergo four stages: frozen‐sheath formation, rapid melting, alternation of melting and solidification, and disappearance. Its corresponding cross‐sectional area rapidly increases to a maximum, sharply decreases, oscillates, and eventually reaches zero. The feeding strip effectively mitigates the impingement of jet onto the narrow surfaces of the slab by compressing “lower recirculation” and dividing “upper recirculation” of molten steel near submerged entry nozzle, especially at higher feeding strip velocities. Furthermore, there exists the additional cooling effect region of strip feeding in the temperature field of slab, which is caused by the melting of strip and molten/shedded‐strip flow. As feeding strip velocity increases, the cooling effect region moves correspondingly from the vicinity of the narrow surfaces of the slab to the center of slab.

Cooling Capacity Evolution of Steel Strip during Oscillatory Feeding Process in Slab Continuous Casting

Zhang

Zhu

et al. 2023

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To comprehensively understand the effect of oscillation on cooling capacity of steel strip, a mathematical model is proposed to investigate the distribution of temperature fields in continuous cast slabs, taking into account the oscillatory feeding process. Strip oscillation results in a periodic variation of nearby molten steel flow. It intensifies the turbulence of surrounding molten steel and enhances the interfacial heat transfer. During the feeding process, the morphology of strip undergoes three stages: upheaval, fluctuation, and disappearance. As the strip oscillation frequency increases, the maximum cross‐sectional area of the strip gradually decreases during the upheaval stage, the fluctuation stage gradually disappears, and the strip disappearance speed gradually increases during the disappearance stage. These observations suggest that an increase in the oscillation frequency accelerates the melting of the strip, which is caused by the enhanced heat transfer between the strip and molten steel. This results in a gradual growth of strip's cooling capacity and a decrement in the liquid fraction of molten steel surrounding the strip. In addition, feeding strip is advantageous in preventing the jet from impinging onto narrow surfaces of slab. The blocking effect initially increases and then remains almost unchanged as the strip oscillation frequency increases.