用于不锈钢冶炼的硝酸盐类发泡剂

 针对目前电炉冶炼不锈钢时采用发泡剂造泡沫渣的需求和硝酸盐在高温下分解能够提供更充足气源的优点,在实验室中频感应炉中对选定的低氟硝酸盐型发泡剂进行了正交试验,以考察其发泡性能。通过对各因素影响发泡效果强弱的分析,得到了其作用的强弱依次为：发泡剂加入量＞w(Cr2O3)＞碱度＞硝酸钙与碳的质量比。此外还通过模式识别方法对发泡剂成分进行优化,得到了适合工艺操作的合理配方。     

LF低氟泡沫渣精炼性能实验研究

对LF用低氟泡沫渣的精炼性能进行了实验研究。CaO—A12O3—SiO2系精炼渣的精炼性能和发泡性能存在一定的冲突，需要根据实际生产的要求加以综合考虑。实验中得到合适的LF泡沫精炼渣的组成为，％：CaO45～60，A12O3 30-40．SiO2 10-15，MgO5～10，曼内斯曼指数MI在0.15左右。     

高炉富Al2O3炉渣性能分析及优化

南钢高炉炉渣Al2O3偏高，炉渣流动性差，被迫采用高炉温操作，影响了技术经济指标的进一步提高。本叙述了现场渣样实验室的粘度测定结果，讨论了各种成分及炉渣碱度对粘度影响的实验室研究结果，在此基础上分析讨论了南钢高炉炉渣性能优化的方向和措施。     

Al2O3-CaO基预熔精炼渣吸收Al2O3夹杂的动力学研究

通过改进的粘度测试装置，测试和研究了成分(％)为：4-10MgO，34-39Al2O3，33042CaO，3-9CaF2，8SiO2，1．3-8．7SrO精炼渣中Al2O3圆柱体旋转线速度对Al2O3夹杂熔解速度的影响和Al2O3在渣中的熔解速度常数。结果表明，降低精炼渣粘度和减少渣中初始Al2O3含量，有利于提高精炼渣吸收Al2O3的能力。     

灰成分对焦炭热性能的影响

通过在配煤中分别加入不同量的Fe2O3、CaO、MgO、K2O、Na2O、SiO2、Al2O3、P2O5、TiO2改变灰成分的炼焦试验，和大量的模拟生产配煤的炼焦试验。获得169组试验数据，采用回归分析的方法获得了宝钢煤源条件下，焦炭灰成分中十大主要成分对焦炭热性能影响的次序。确立了适合宝钢煤源条件的灰催化指数ACI计算方法。建立了焦炭灰成分对焦炭热性能影响的数学模型。     

高铝钢包渣粘度的计算研究

利用Factsage软件和修正后的Einstein-Roscoe公式计算了高铝钢包渣CaO-SiO2-MgO-Al2O3体系的粘度及相图。计算研究了碱度(R=CaO/SiO2)、MgO含量和Al2O3含量对钢包渣粘度的影响,结合炉渣结构理论对其进行了解释。研究结果表明,在高铝钢包渣中,提高碱度可以降低钢包渣的粘度;在R=1.9时MgO含量增加会增大钢包渣的粘度,R=3时MgO含量增加对粘度影响较小;在碱度大于2时,粘度随Al2O3含量的增加呈现先降低后升高的趋势。要使钢包渣获得良好的流动性,需要控制渣的成分:当Al2O3含量在20 wt%~30 wt%范围,碱度R可控制在3~4之间;当Al2O3含量大于30 wt%、碱度R应大于4。     

LF精炼渣发泡性能的实验研究

采用钼丝挂渣法对CaO Al2O3渣系LF精炼渣的发泡指数进行了测定。结果表明:熔渣中表面活性组无SiO2可以促进渣的泡沫化;高熔点的2CaO·Al2O3·SiO2可增加渣的粘度,从而延长泡沫的持续时间;低含量的CaF2(<5%)会明显改善熔渣的泡沫化性能;另外,较低的温度和炉渣低氧化性以及分批加入渣料等都有利于形成泡沫渣。     

Al2O3对CaO—“FeO”—SiO2—CaF2熔渣粘度的影响

在1714K－1757K温度范围内利用旋转圆柱法测试了CaO-“FeO”-SiO2-CaF2渣系粘度随着不同的Al2O3添加量的变化。第一步试验是对添加少量Al2O3达到平衡条件下进行的粘度测试。为了比较该结果采用一种工业用结晶器保护渣进行了类似的试验。对于这两种情况，发现在所有实验温度下粘度均随着Al2O3添加量的增加而增加，且增加的粘度与添加的Al2O3呈线性关系。对于工业用结晶器保护渣，添加2－6％Al2O3甚至会导致粘度大幅增加。采用上述系列熔渣在动态模型中也进行了等温试验。这里，熔渣粘度的变化用来监测连续不断地溶解在渣中的一种Al2O3圆盘与时间的函数关系。这样设计试验是为了溶解铝主要沿着垂直方向进行，按照试验后熔渣外形和粘度变化的速率讨论了Al2O3溶解的速率。Al2O3圆盘试验显示了渣的组分在固态Al2O3中的扩散及Al2O3的溶解是由熔渣中的固体物溶解产生的。     

含B2O3无氟连铸保护渣物理性能的研究

常规保护渣中配入的助熔剂一般是氟化物和Na2O,但二者都对环境产生严重污染。为此试验研究了含助熔剂B2O3保护渣及其熔点、粘度、结晶性能和表面张力等物理性能。试验表明，当保护渣碱度(CaO/SiO2)等于0．88，成分(％)为37．91CaO-43.09SiO2—5Al2O3—5MgO-2Li2O-7B2O3时的熔点909℃，熔化性温度1160℃，1300℃粘度值0．40Pa．s,1300℃表面张力值0．32N/m，能满足常规钢种和部分特殊钢种对连铸保护渣的使用要求。     

复合渣的粘度和精炼特性的预测

借助于银的溶解工艺研究了熔渣的碱度与物化性能 (例如粘度和精炼特性 )的关系。根据渣的碱度讨论了理论评价熔渣成分的基本原则。在 Mo- B2 O3 (Mo=Ca O,Ba O,Na2 O) ,Ca O- RO(RO=B2 O3 ,Si O2 ,Al2 O3 )及 Ca O- Al2 O3 - Ca F2 渣系中 ,利用银的不同溶解度评价了碱性氧化物及与 Ca F2 和 B2 O3 有关的酸性氧化物的相对碱度。通过每种化合物的相对碱性值可以得到复合渣的综合碱度 ,并预测出熔渣的粘度和精炼特性。此外 ,可根据精炼特性的目标值确定渣系的最佳组成 ,并讨论了设计渣系的基本原理。复合渣的粘度和精炼特性的预…     

Petrographic and thermodynamic study of slags in EAF stainless steelmaking

Abstract

A study of the typical characteristics of electrical arc furnace (EAF) slags in the production of the stainless steel (AISI 304L) was carried out. Twenty-eight slag samples were taken from 14 heats. Simultaneously with each slag sampling, the temperature of the steel was measured, and one steel sample was taken. The selected slag samples were studied both using SEM–EDS and light optical microscopy. Computational thermodynamics was used as a tool to predict the equilibrium phases in the top slag as well as the amount of these phases at the process temperatures. It was observed that, at process temperature, the stainless EAF slag generally consists of liquid oxides, spinel particles and metallic droplets. Under normal operation, the amount of spinel particles is 2–6 wt-%. In addition, the influence of the slag temperature, basicity, MgO content and Cr₂O₃ content on the amount of spinel precipitates and thereby on the foaming index of the top slag is also illustrated and discussed. More specifically, it was found that, within the compositional range of the slag samples, the critical parameter affecting the amount of solid spinel particles in the slag is the chromium oxide content.     

Petrographical study of microstructural evolution of EAF duplex stainless steelmaking slags

Abstract

A novel study to characterise electric arc furnace (EAF) slags in the production of duplex stainless steel at the process temperatures was performed. The investigation is focused on determining the microstructural evolution of the EAF slag during and at the end of the refining period. In this regard, slag sampling was done at three stages from seven EAF duplex stainless steel heats (21·5–22·5?wt‐%Cr, 1·6–5·7?wt‐%Ni and 0·3–3·2?wt‐%Mo). More specifically, the samples were collected before FeSi addition, after FeSi injection and just before tapping. Collected samples were analysed by light optical microscopy and SEM energy dispersive X‐ray spectroscopy to characterise the high temperature microstructure of the slag phases. In addition, X‐ray diffraction analysis was used to verify the petrographical results. It was observed that at all process stages, the duplex steel slag contains molten oxides, magnesiochromite spinels and metallic droplets. However, before the FeSi addition, the slag also contains calcium chromite crystals. In this stage, the slag has a high viscosity, which drops to lower level after FeSi injection. Furthermore, depending on the basicity, the slag may contain other solid phases such as perovskite and calcium silicate.     

Foaming of slags under dynamic conditions

Slag foaming under dynamic conditions has been studied in laboratory scale to examine the influence of properties commonly used to describe the foaminess and foam stability of slags under steady-state conditions. Synthetically produced slags with compositions relevant to tool steel and stainless steel production were studied through X-ray equipment in measurements simulating the dynamic conditions found in real processes. It is found that the dynamic systems display a more complex behavior than systems under steady state. Traditional theories for foaming do not seem to be valid for slag foaming under dynamic conditions. The foam displays a fluctuating behavior, which the presently available models are not able to take into account. The concept of a foaming index does not seem to be applicable, resulting in the need for alternative models.     

不同冶炼工艺的A286沉淀硬化不锈钢中夹杂物对比探讨

A286奥氏体沉淀硬化不锈钢(国内也称GH2132高温合金)是一种应用广泛的650 ℃以下使用的高温紧固件材料。该材料在实际生产使用中,使用了电炉+炉外精炼+电渣重熔(EAF+LF+ESR)和真空感应+真空自耗(VIM+VAR)两种冶炼生产工艺,而到目前为止国内对这两种工艺生产的A286不锈钢材料还未进行系统的对比研究。实验将以上两种冶炼工艺的A286试验钢作为研究对象,使用Aspex夹杂物分析仪、扫描电镜(SEM)等试验工具,对两种试验钢的组织,非金属夹杂物的种类、成分、粒径大小及分布、形态等差异及特点进行了对比研究。结果表明,EAF+LF+ESR冶炼的试验钢中的夹杂物数量、面积是VIM+VAR工艺试验钢的3倍以上;两种试验钢中的夹杂物均有TiC、TiN、Ti(C,N)等种类,前者的夹杂物以TiN夹杂物为主,且多为大尺寸链状,纵横比较大,形状较复杂,对材料室温力学性能和耐腐蚀性能不利;后者的夹杂物以TiC为主,尺寸较小且形状较简单。通过将A286试验钢中的N质量分数控制在0.001%以下,可以将含Ti夹杂物的数量、大小等控制在较低的水平。EAF+LF+ESR工艺由于自身工艺特点,试验钢中P含量较高,约为VIM+VAR工艺试验钢P含量的10倍,据资料可能有利于A286不锈钢的高温蠕变性能。研究结果可为在不同环境和服役要求下使用A286不锈钢提供技术参考。     

Study on the foaming of CaO-SiO2-FeO slags: Part II. Dimensional analysis and foaming in iron and steelmaking processes

An empirical equation for the foaming index Σ of a CaO-SiO₂-FeO slag was obtained by dimensional analysis. The effect of second-phase particles on slag foaming was well described by calculating the viscosity of the mixture using the modified Einstein equation. The anticipated foaming in basic oxygen furnace (BOF), electric arc furnace (EAF), and bath-smelting processes was estimated using the parameter Σ for various operating conditions and slag compositions. For BOF operations, it is predicted that foaming is most extreme in the middle of the blow, and a stable foam in EAF is achieved with less basic slags with low FeO contents. For bath smelting, foam heights of 5 m are possible, and a higher degree of prereduction prior to smelting will reduce foaming (because of smaller gas evolution) and possibly increase production rates. Running the process at a higher pressure will also reduce foam heights, because the volume of gas generated is less. Kimihisa Ito, Research Associate, formerly with the Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University     

不同冶炼工艺的A286沉淀硬化不锈钢中夹杂物对比探讨

A286奥氏体沉淀硬化不锈钢(国内也称GH2132高温合金)是一种应用广泛的650 ℃以下使用的高温紧固件材料。该材料在实际生产使用中,使用了电炉+炉外精炼+电渣重熔(EAF+LF+ESR)和真空感应+真空自耗(VIM+VAR)两种冶炼生产工艺,而到目前为止国内对这两种工艺生产的A286不锈钢材料还未进行系统的对比研究。实验将以上两种冶炼工艺的A286试验钢作为研究对象,使用Aspex夹杂物分析仪、扫描电镜(SEM)等试验工具,对两种试验钢的组织,非金属夹杂物的种类、成分、粒径大小及分布、形态等差异及特点进行了对比研究。结果表明,EAF+LF+ESR冶炼的试验钢中的夹杂物数量、面积是VIM+VAR工艺试验钢的3倍以上;两种试验钢中的夹杂物均有TiC、TiN、Ti(C,N)等种类,前者的夹杂物以TiN夹杂物为主,且多为大尺寸链状,纵横比较大,形状较复杂,对材料室温力学性能和耐腐蚀性能不利;后者的夹杂物以TiC为主,尺寸较小且形状较简单。通过将A286试验钢中的N质量分数控制在0.001%以下,可以将含Ti夹杂物的数量、大小等控制在较低的水平。EAF+LF+ESR工艺由于自身工艺特点,试验钢中P含量较高,约为VIM+VAR工艺试验钢P含量的10倍,据资料可能有利于A286不锈钢的高温蠕变性能。研究结果可为在不同环境和服役要求下使用A286不锈钢提供技术参考。     

Process dynamics of electric arc furnace during direct reduced iron melting

A phenomenological mathematical model to simulate steelmaking operations in an electric arc furnace (EAF) has been developed. This model has been validated with industrial data from a Mexican company that employs direct reduced iron (DRI) as the main iron unit. The slag and steel composition can be predicted in real time with the aid of several components integrated into the simulator. The model starts with the optimization of mass and energy balances that yields the requirement of materials to produce a given quality of steel with the minimum cost. The rate of reduction of iron oxide is computed based on two reactions occurring between the FeO and carbon dissolved in the metal and FeO with the carbon particles injected into the slag. A mechanism of consumption of carbon particles has been completed, which includes the effect of surfactant species in the slag and operational variables of the industrial practice of carbon injection. A new concept, called dynamic foaming index, (DFI) is proposed to quantify the actual foaming behavior of industrial slags throughout a commercial heat. The results prove the versatility and robustness of the present mathematical model and provide a knowledge base to assist in the design, operation, and optimization of metallurgical practices for EAF steelmaking.     

EAF 留碳操作生产中、高碳钢的工艺实践

在70tEAF-LF-CCM 流程生产50CrVA、60Si2Mn、77Mn 等中、高碳钢时,EAF 炼钢过程采用 20%～30%热装铁水,控制供氧强度,二元渣碱度1.8~2.8可有效进行留碳操作。生产统计表明,EAF 留碳 操作终点C 为0.25%～0.53%,P为0.006%~0.015%,钢水温度1593～1625℃。 EAF 留碳操作虽使冶炼 周期延长5～10 min,但LF 喂丝量降低1/2以上,显著降低冶炼成本和提高钢水质量。     

Effect of Iron Redox Equilibrium on the Foaming Behavior of MgO-Saturated Slags

In this study, the foaming index of CaO-SiO₂-Fe_tO and CaO-SiO₂-Fe_tO-Al₂O₃ slags saturated with MgO was measured to understand the relationship between their foaming behavior and physical properties. The foaming index of MgO-saturated slags increases with the Fe_tO content due to the redox equilibrium of Fe_tO. Experimental results indicated that MgO-saturated slag has relatively high ferric ion concentration, and the foaming index increases due to the effect of ferric ion. Therefore, the foaming behavior of MgO-saturated slag is more reasonably explained by considering the effect of ferric ion on the estimation of slag properties such as viscosity, surface tension, and density. Specifically, the estimation of slag viscosity was additionally verified by NBO/T, and this is experimentally obtained through Raman spectroscopy.