The Influence Of Slag Oxidation On Nitrogen Recovery In Nitrogen-containing Stainless Steel

High-nitrogen steel is favored by people for its low price and excellent comprehensive properties,the addition of nitrogen-containing alloy is one of the effective ways to smelt high-nitrogen steel.This article is based on the Ca O-Si O₂-Al₂O₃-Mg O-Cr₂O₃-Fe₂O₃-Ca F₂ slag system to explore the effects of alkalinity,Cr₂O₃,Fe₂O₃ and the amount of added slag on the nitrogen yield during the alloying process of 304 stainless steel with Mn N.Firstly,Factsage software is used to calculate the high temperature area of the experimental slag system and determine the composition of the slag system.Combining thermodynamic calculations to analyze the melting temperature and viscosity of the experimental slag;use spark direct reading spectrometer,nitrogen oxygen analyzer and X-ray diffractometer to detect the nitrogen and chromium content in the experimental steel and the phase of the experimental steel slag;finally through field emission scanning The electron microscope counts and analyzes the inclusions in the experimental steel.The melting temperature of the experimental slag is proportional to the theoretical melting temperature.The basicity increased from 1.5 to 3.0,the melting temperature of the experimental slag first increased from 1335°C to 1380°C and then decreased to 1307.5°C.The theoretical melting temperature of the experimental slag rose from 1290°C to 1327.5°C and then decreased to 1230°C;Fe₂O₃ and Cr₂O₃ content The increase of has little effect on the melting temperature.The melting temperature of the experimental slag is basically the same as the theoretical total amount of precipitates.The alkalinity changes from 1.5 to 2.5,and the melting temperature does not fluctuate much around 1351±1°C.When the alkalinity reaches 3.0,the melting temperature decreases to 1301°C,the theoretical total amount of precipitates changes with the alkalinity trend from 80±6%to 11.046%;Fe₂O₃ changes have little effect on the melting temperature;with the increase of Cr₂O₃ content,the melting temperature decreases from 1342±2℃to 1323℃and then increases to 1348℃,the total amount of theoretical precipitates decreased from 61±2%to 53.256%and then increased to 73.481%.Combining thermodynamic calculations and orthogonal test range analysis,it is found that the degree of influence on the yield of nitrogen in the experimental steel is from high to low:alkalinity>Fe₂O₃>Cr₂O₃>addition of slag;the optimal group selects alkalinity as 2.5,Fe₂O₃ as2.5%,Cr₂O₃ is 3.0%,and the amount of slag added is 2.5%,the nitrogen recovery rate is66.906%.There are Ca Si O₃,Mg₂Si O₄ and Mg Al₂O₄ in the steel slag with low nitrogen yield,and the remaining steel slag with high nitrogen yield is Ca₂Al₂Si O₇.The increase in slag basicity,Fe₂O₃,Cr₂O₃ and the amount of added slag is conducive to the adsorption of the slag on the number of inclusions,but has little effect on the size of the inclusions.By changing the alkalinity and Fe₂O₃,it is found that the inclusions in the experimental steel are mainly composed of Mn S,Mn O-Cr₂O₃-Si O₂-Mn S,Mn O-Cr₂O₃-Si O₂-Mn S-Al₂O₃,Mn O-Cr₂O₃-Si O₂-Mn S-Cr N,drawing Mn O-Si O₂-Cr₂O₃ ternary phase diagram found that the inclusions are basically distributed in Cr₂O₃-Slag liq,Cr₂O₃-Mn O-Slag liq and Cr₂O₃-Si O₂-Slag liq.According to the above conclusions,the coverage of slag is conducive to the improvement of the yield of nitrogen in steel,and the addition of Cr₂O₃ in the slag can reduce the burning loss of chromium in the steel.For the inclusions in the steel,covering the slag can effectively reduce the inclusions in the steel.However,the experimental slag has little effect on the size and composition of inclusions in steel.