微小气泡去除夹杂物技术研究

发布时间：2018-06-05 15:56

本文选题：炼钢 + 精炼　；参考：《北京科技大学》2017年博士论文

【摘要】：气泡去除夹杂物是有效促进钢液中夹杂物去除的精炼手段之一。在钢液中生成大量弥散微小气泡是气泡精炼的关键所在。本文研究的微小气泡去除夹杂物是一种去除钢液中显微夹杂物的新技术,其技术原理是前期将钢液置于氮气或氢气分压较高的环境中,使钢液中氮或氢含量显著增加,后期通过迅速减压,过饱和溶解气体以夹杂物为核心生成大量弥散微小气泡,最后气泡携带夹杂物上浮,并在上浮过程中不断捕捉细小夹杂物,显著地促进钢液中显微夹杂物去除。目前关于此技术的理论基础研究报道稀缺。鉴于此情况,本文主要研究了五个方面：(1)钢液中气泡形核热力学：(2)钢液中气泡析出过程机理；(3)钢液中气泡生长动力学；(4)析氮过程钢液中气泡分布规律：(5)增氮析氮过程不同工艺因素对钢中显微夹杂物的影响。通过以上这些研究,得到了以下结论。(1)基于经典凝固形核理论,研究了钢液/(N_2、H_2)过饱和体系中气泡形核机理。分别推导气泡均相和异相形核临界半径表达式,并分析了钢液深度、前期增氮/氢和后期真空处理压力等因素对气泡形核临界半径的影响。结果表明气泡均相和异相形核具有相同的形核临界半径表达式,但异相形核气泡体积为均相形核球体的一部分,气泡更易于在与钢液润湿性较差的夹杂物表面异相形核：钢液深度越大,气泡形核临界半径越大,随着钢液深度的增加影响逐渐加强；前期增氮/氢压力越高,气泡自发形核及形成不同尺寸气泡核的临界钢液深度越大；后期真空处理压力对气泡自发形核及形成不同尺寸气泡核的临界钢液深度影响较小。(2)采用水模型实验研究了钢液/(N_2、H_2)过饱和体系中气泡析出过程机理。结果表明后期真空减压处理过程中,单个或聚集成团的夹杂物可为过饱和溶解气体析出形成气泡提供异相形核核心；气泡在夹杂物表面迅速析出长大,而且长大过程中始终保持球状。(3)采用水/CO_2体系模拟研究钢液/(N_2、H_2)过饱和体系中气泡生长动力学行为。结果表明采用微小气泡去除夹杂物技术时,前期增氮/氢压力的增加对气泡生长有显著促进作用：后期真空处理压力的增加对气泡生长有阻碍作用,且随着后期真空处理压力的增加影响逐渐加强；钢液深度的增加对气泡生长有阻碍作用,且随着钢液深度的增加影响逐渐减弱：相比氮气,钢液中氢气气泡析出长大更快。(4)析氮过程钢液中气泡分布实验结果表明,增氮钢液经析氮及急冷处理后距离钢锭上表面不同位置处横截面均有气泡产生,气泡粘附的夹杂物主要为单个棱角状的纯Al_20_3,尺寸约为10-20μm；靠近钢锭上表面附近处金属致密度最小,其他位置处金属致密度相差较小：随着距钢锭上表面距离的增加,气泡平均尺寸减小,气泡数量增加。(5)增氮析氮过程钢中显微夹杂物去除实验结果表明,钢液经增氮析氮处理后钢中全氧和显微非金属夹杂物去除效果显著；真空处理时间越长,钢中全氧和显微非金属夹杂物数量越低,尤其当充氮压力为0.5x10~5 Pa以及真空处理时间为30 mmin时钢中全氧去除率达到了81.6%,由析氮前38x10~(-6)降至7×10~(-6)。
[Abstract]:A new technique for removing inclusions in molten steel by bubble removal is one of the key techniques to remove inclusions in molten steel . It is a new technique to remove micro - inclusions in molten steel .
( 3 ) the bubble growth kinetics in molten steel ;
( 4 ) The distribution law of bubbles in molten steel is analyzed : ( 5 ) The influence of different technological factors on the microscopic inclusions in steel is obtained .
The higher the nitrogen / hydrogen pressure in the early stage , the greater the bubble spontaneous nucleation and the critical steel liquid depth forming the bubble nuclei of different sizes ;
( 2 ) The mechanism of bubble separation in the supersaturated system of molten steel / ( N _ 2 , H _ 2 ) was studied by using water model experiment .
The results show that the increase of nitrogen / hydrogen pressure in the early stage plays an important role in the growth of the bubble , and the influence of the increase of the vacuum processing pressure is gradually strengthened with the increase of the vacuum processing pressure in the late stage .
The increase of the depth of molten steel has an obstacle to the growth of the bubble , and decreases with the increase of the depth of molten steel . Compared with the nitrogen , the evolution of hydrogen bubbles in the molten steel is faster . ( 4 ) The experimental results of the bubble distribution in the steel liquid during the nitrogen evolution process show that the gas bubbles are generated at different positions on the upper surface of the steel ingot after the nitrogen evolution and the quenching treatment , and the inclusion of the bubbles is mainly a single angular pure Al _ 20 _ 3 , and the size is about 10 - 20渭m ;
The metal density of steel near the upper surface of steel ingot is the least , the difference of metal density in other positions is small : with the increase of the distance from the upper surface of the ingot , the average size of the bubble decreases and the number of bubbles increases .
The longer the vacuum treatment time , the lower the total oxygen content and the non - metallic inclusions in the steel , especially when the nitrogen filling pressure is 0.5 脳 10 ~ 5 Pa and the vacuum treatment time is 30 mmin , the total oxygen removal rate in the steel reaches 81.6 % , which is reduced to 7 脳 10 ~ ( -6 ) by the nitrogen evolution .
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TF703

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