适用于冷轧薄板类钢种的合理炉外精炼工艺的探讨

炉外精炼过程钢液氧含量对脱硫效率影响显著,对冷轧薄板钢种如在LF中进行深度脱硫,由于必须将钢液氧含量降至很低水平,容易造成钢中硅含量超标等问题.采用LF工艺不能很好地解决既能强烈搅拌钢水促进夹杂物去除又能防止钢水被炉渣和炉气氧化的矛盾,因此须对炉渣进行还原改质处理,同时会导致生产成本增加和转炉连铸机生产节奏变慢等问题.采用CAS和RH精炼工艺能够在防止钢水被炉渣和炉气氧化的前提下,强烈地搅拌钢水以促进夹杂物上浮,生产节奏也能适应大型转炉炼钢和快速板坯连铸需要.对于LCAK、ELC、ULC等冷轧薄板钢种,应以采用CAS和RH精炼工艺方法为主导.     

适用于转炉-薄板坯连铸钢厂的合理炉外精炼工艺的探讨

转炉薄板坯连铸钢厂采用LF炉外精炼工艺,其生产节奏与转炉炼钢和薄板坯连铸不相适应。生产冷轧钢种时还存在钢液w（[Si]）、w（[N]）偏高而影响钢材冷加工性能的问题。转炉薄板坯连铸钢厂的炉外精炼应主要采用CAS和RH精炼工艺,对于绝大多数热轧类钢种,可以通过铁水脱硫预处理、抑制转炉炼钢回硫、转炉出钢脱硫等方法生产出硫含量符合要求的铸坯。对冷轧类钢种可采用传统流程炉外精炼工艺,即根据钢种碳含量要求和用途,选择采用RH或CAS。     

高级别船板钢炉外精炼过程洁净度研究

为了研究采用BOF-LF-RH-CC工艺生产的A32船板钢洁净度水平,进行了三炉工业实验.通过对冶炼过程系统取样分析,研究了钢中总氧、氮含量变化,夹杂物的转变规律及机理.结果表明:该工艺生产的船板钢有较高的洁净度,中包总氧控制在2×10-5以下,氮含量控制在4×10-5以下;LF精炼过程中,钢中总氧、夹杂物数量密度和平均尺寸均降低,夹杂物转变为CaO-MgO-Al₂O₃三元系;RH精炼过程中,钢中总氧和夹杂物数量密度降低,而夹杂物平均尺寸升高;钙处理过程中,夹杂物数量密度升高,而夹杂物平均尺寸降低,夹杂物转变为CaO-Al₂O₃-CaS三元系.      

Investigation on Non-Metallic Inclusions in LCAK Steel Produced by BOF-LF-FTSC Production Route

 The behavior of non-metallic inclusions in LCAK (low carbon aluminum killed) steel produced by BOF (basic oxygen furnace)-LF (ladle furnace) refining-FTSC (flexible thin slab continuous caster) production route was investigated. The results showed that, LF refining for LCAK steel could decrease the wT[O] significantly, and the inclusions were modified by Ca treatment, which prevented nozzle clogging efficiently. However, owing to the unstable casting condition in the earlier stage of casting, a severe reoxidation occurred, accompanied with mold slag entrapment. The transformation of non-metallic inclusions during the steelmaking process was Al2O3→MgO-Al2O3 type inclusion→MgO-Al2O3-CaO type inclusion with a CaS ring, and the mechanism of the transformation was proposed and discussed via thermodynamic and kinetic analysis. Besides, to avoid CaS precipitation, the product of w2[Al]×w3[S] in steel should be less than 2.0×10-10 at 1873 K, which remands higher desulfurization ratio during LF refining.     

低碳铝镇静钢LF精炼过程钢中非金属夹杂物的研究

对LF精炼过程低碳铝镇静钢水中非金属夹杂物的变化进行了研究,发现在采用高碱度、强还原性炉渣条件下,Al2O3类夹杂物先向MgO-Al2O3系夹杂物并进而向CaO-MgO-Al2O3系夹杂物和CaO-CaS-Al2O3系夹杂物转变。在LF精炼结束时,钢中已基本没有对钢水可浇性影响最大的Al2O3系夹杂物,因此可以减少LF精炼后对钢水进行钙处理用的钙线量,以降低生产成本并减少由于钙处理而生成的大尺寸钙铝酸盐夹杂物的数量。     

不同钢种炉外精炼钙处理工艺的选择

 为了优化不同钢种的LF精炼钙处理工艺，研究了高强结构钢、低碳结构钢、焊瓶钢、耐磨钢、高碳钢在LF精炼及钙处理过程中夹杂物的演变机理。结果表明,渣 钢反应时间越长，钙处理前的夹杂物变性越彻底。钙处理前焊瓶钢夹杂物以Al2O3为主，高强结构钢、低碳结构钢夹杂物以MgO Al2O3 CaO复合夹杂为主；高碳钢、耐磨钢夹杂物以低熔点的Al2O3 CaO夹杂为主。钙处理工艺会增加钢液中夹杂物数量及尺寸。控制Al2O3 SiO2 MnO复合夹杂物的关键是避免LF精炼中后期进行硅锰合金化。综合考虑各方面因素，建议焊瓶钢增加当前的钙线喂入量，高强结构钢、低碳结构钢使用轻钙处理工艺，高碳钢、耐磨钢取消钙处理工艺。     

RH强制脱碳与自然脱碳工艺生产IF钢精炼效果分析

西昌钢钒厂由于转炉热量不足而以转炉—LF精炼—RH精炼—连铸工艺生产IF钢,为探究RH强制脱碳与自然脱碳工艺生产IF钢精炼效果,采用生产数据统计、氧氮分析、夹杂物自动扫描、扫描电镜和能谱分析等手段,对不同脱碳工艺对顶渣氧化性以及钢的洁净度影响进行了详细研究。结果表明:（1）与自然脱碳工艺炉次相比,采用强制脱碳工艺的炉次在转炉结束与RH进站钢中的平均[O]含量更低;（2）两种工艺脱碳结束钢中的[O]含量基本在同一水平;（3）强制脱碳工艺的炉次在RH结束时渣中平均T.Fe的质量分数降低了1.3%。在能满足RH脱碳效果的前提下,尽量提高转炉终点钢液碳含量、降低钢液氧含量,后续在RH精炼时采用强制吹氧脱碳工艺,适当增大吹氧量来弥补钢中氧,可显著降低IF钢顶渣氧化性。自然脱碳工艺与强制脱碳工艺控制热轧板T.O含量均比较理想;与自然脱碳工艺相比,强制脱碳工艺可有效降低IF钢[N]含量,这与强制脱碳工艺真空室内碳氧反应更剧烈所导致的CO气泡更多和气液反应面积更大有关。脱碳工艺对IF钢热轧板中夹杂物类型、尺寸及数量没有明显影响,夹杂物主要由Al₂O₃夹杂、Al₂O₃–TiO_x夹杂与其他类夹杂物组成,以夹杂物的等效圆直径表示夹杂物尺寸,以上三类夹杂物平均尺寸分别为4.5、4.4和6.5 μm,且钢中尺寸在8 μm以下的夹杂物数量占比高于75%。在RH精炼过程中,尽量降低RH脱碳结束钢中[O]含量,有利于提高钢液洁净度。      

鞍钢RH轻处理钢种生产工艺实践

介绍了鞍钢股份有限公司炼钢总厂四工区采用铁水预处理—顶底复吹转炉冶炼—RH精炼生产低碳低硅铝镇静钢的工艺实践。实践表明,采用该工艺后,缩短了精炼处理周期,提高了钢水的洁净度,有效缓解了RH-LF双联工艺对吊车和LF精炼的压力,保证了生产组织的平稳顺行。     

RH精炼过程中吹氧量对IF钢洁净度的影响

无间隙原子钢（IF钢）主要用于汽车、家电等行业,除需要极低的C、N含量外,对最终产品的表面质量也有严格要求。钢中O含量和夹杂物对产品的表面质量影响很大。快速降低钢中C含量、同时保证钢的高洁净度是非常重要的。为此,通过在Ruhrstahl Hereaeus（RH）精炼?连铸过程密集取样,采用ASPEX扫描电镜详细研究了RH吹氧强制脱碳工艺下吹氧量对IF钢洁净度的影响。结果表明,本实验条件下,吹氧量对精炼?连铸过程中夹杂物的类型和形貌没有影响。吹氧量对RH精炼前期（加Al后4 min内）钢液洁净度影响较大,而对后期生产过程中钢液的洁净度影响不大;精炼前期,吹氧量高,钢液中总氧（T.O）含量和夹杂物的量增加。簇群状夹杂物主要出现在RH破空之前,真空精炼结束后钢液中很难发现簇群状夹杂物。中间包钢液洁净度与RH吹氧量相关性不大,而与加Al脱氧前钢液中O含量相关性很大,加Al脱氧前钢液中O含量高,中间包钢液洁净度差;为提高中间包钢液的洁净度,应尽量减少加Al脱氧前钢液中的O含量。随着生产的进行,钢液中T.O含量、夹杂物的量呈下降趋势,洁净度逐渐提高。      

脱氧工艺对低碳铝镇静钢洁净度的影响

 以KR→BOF→RH→CC流程生产的低碳铝镇静钢,在转炉流程后采用2种不同脱氧工艺：出钢添加部分铝预脱氧,RH真空循环利用钢中碳脱氧,后加铝强脱氧（工艺Ⅰ）;出钢加铝强脱氧,RH真空循环处理（工艺Ⅱ）。对两种脱氧工艺出钢后的顶渣改质效果进行对比分析,结合全氧分析,利用ASPEX扫描电镜对两种工艺下RH真空处理过程的夹杂物和铸坯内外弧表层夹杂物的形貌、成分、数量和尺寸进行系统研究。结果表明,工艺Ⅱ的顶渣改质效果优于工艺Ⅰ;经过RH真空处理,两种工艺均可以明显地去除20 μm以上的夹杂物;在RH精炼阶段、铸坯及热轧板表层的夹杂物尺寸、数量密度以及总氧控制方面,工艺Ⅱ优于工艺Ⅰ。     

CAS精炼效果分析

从钢水洁净度、铸坯质量、夹杂物含量等方面对某钢厂CAS精炼效果进行了分析并与RH真空精炼效果进行对比。结果表明,CAS精炼产品夹杂物总量和氮、氧含量与RH轻处理产品相当,但该厂CAS精炼产品B类夹杂物（氧化铝）含量稍微偏多,原因是因为该厂钢包底吹位置较偏,罩内流场不太理想造成。试验结果还表明,采用CAS处理的某低碳钢,力学性能完全满足标准要求。     

Cleanliness of GCr15 bearing steel refined by RH and VD vacuum processes

The cleanliness of GCr15 bearing steels produced by RH and VD vacuum refining processes was compared. Evolutions of total oxygen (TO), total nitrogen (TN), total sulfur (TS), and inclusions were investigated. Bearing steel has high requirements for cleanliness. RH refining has advantages in reducing TO and TN content, removing solid inclusion, and circulating efficiency. After RH refining, the TO content in molten steel decreased by 61%, the TN content decreased by 15%, and the number density of inclusions decreased by 75%. The stirring of slag and steel was strong during the VD refining, which was beneficial to the desulfurization, the TS content in liquid steel decreased by 50%. The circulation rate of the liquid steel in the VD refining was much lower than that in RH refining. The stronger stirring of slag and steel during VD refining resulted in the slag entrainment. The contact angle between inclusions with different liquid phase fractions and liquid steel is different. Inclusions with liquid phase fraction less than 27% are not wetted with liquid steel and are easy to collide, grow and float up for removal, while the adhesion work of liquid inclusions is greater and difficult to remove from liquid steel.     

齿轮钢中非金属夹杂物控制技术研究

为了降低钢的T[O]含量和生成较低熔点的非金属夹杂物以改善合金结构钢的抗疲劳破坏性能,在炉外精炼中采用了高碱度和高Al2O3含量的渣系.研究发现LF和RH精炼结束时钢液T[O]含量均随炉渣碱度增加而降低,在炉渣Al2O3含量低于25%时,T[O]随炉渣Al2O3含量减少而降低,而当炉渣Al2O3超过25%后,T[O]则随炉渣Al2O3含量增加而降低.精炼过程钢液中夹杂物按"Al2O3系夹杂物→MgO-Al2O3系夹杂物→CaO-MgO-Al2O3系夹杂物"顺序发生转变,其中MgO-Al2O3系夹杂物向CaO-MgO-Al2O3系夹杂物的转变是由外向内逐步进行的,转变速度相对较慢,因而致使LF结束时钢中仍存在许多尚未转变的Mgo-Al2O3系夹杂物.钢液T[O]对夹杂物转变有显著影响,降低T[O]含量有利于生成较低熔点的CaO-MgO-Al2O3系夹杂物.     

转炉-精炼-连铸过程钢中氧的控制

结合近年来的文献和笔者的研究工作,概要论述了转炉—精炼—连铸过程中钢洁净度(以总氧含量T[O]表示)的控制及夹杂物对产品质量的影响。提高钢的洁净度应从产生夹杂物的源头抓起,尽可能降低转炉终点氧含量。根据生产统计数据,建立了转炉终点氧预报模型。介绍了硅镇静钢、硅铝镇静钢、铝镇静钢三种脱氧模式及脱氧产物的控制方法。采用钢包精炼方法把夹杂物消灭在钢水进入结晶器之前是获得“干净”钢水的关键。介绍了RH、LF、中间包钢水总氧预报模型。介绍了在连铸过程中防止钢水再污染和进一步去除夹杂物的措施。     

高碳铭GCrl5轴承钢中镁铝夹杂物形成与控制工艺实践

GCr15钢的生产流程为120 t BOF-LF-RH-CC工艺。BOF出钢加200 kg铝块进行强脱氧,同时LF过程控制Al含量至0.030%～0.045%,LF结束夹杂物主要为MgO·Al₂O₃,RH真空后MgO·Al₂O₃夹杂物被去除,钢水中夹杂物以钙铝酸盐为主,但是连铸浇铸过程MgO·Al₂O₃夹杂物又会重新生成。因为LF精炼过程Al-MgO和C-MgO反应的存在,高碳铝脱氧GCr15轴承钢LF精炼结束更容易获得MgO·Al₂O₃夹杂物,并促进中间包钢水MgO·Al₂O₃夹杂物重新生成。当BOF出钢仅加40 kg铝块进行预脱氧,LF结束钢水MgO·Al₂O₃夹杂物数量显著降低,同时中间包钢水中MgO·Al₂O₃夹杂物不再重新生成。此外,将低钛低铝硅铁由出钢过程改为LF过程加入,也可以有效控制钢水中MgO·Al₂O₃夹杂物数量。      

帘线钢冶炼过程夹杂物转变的控制

研究的帘线钢的冶炼流程为150 tLD-RH-LF-软吹氩-CC工艺。通过LD出钢时加入Si-Mn脱氧,并在LF加入低碱度顶渣进行钢渣反应控制钢中非金属夹杂物的塑性。结果表明,RH-LF-中间包和铸坯阶段,钢中主要夹杂物分别为MnO-Al₂O₃-Si0₂(RH),Ca0-Al₂O₃-Si0₂(LF)和MnO-Al₂O₃-SiO₂(中间包和铸坯),采用Si-Mn脱氧和SiC扩散脱氧,低碱度低Al₂O₃顶渣精炼,控制T[O]≤20×10-6,[A1]s≤0.0013%,可有效控制钢中夹杂物数量和尺寸,以及控制夹杂物中Al₂O₃含量并形成可塑性夹杂。     

中厚板钢精炼过程夹杂物的转变

 通过工业试验研究了中厚板钢LF→钙处理→RH精炼过程中夹杂物的转变规律,并对钙处理过程夹杂物转变进行了热力学计算分析。结果表明：精炼过程钢中总氧质量分数降低,夹杂物数量密度降低,夹杂物平均尺寸升高;钙处理后夹杂物为CaO-MgO-Al2O3-CaS四元系;RH破空后夹杂物转变为CaO-MgO-Al2O3三元系,夹杂物中CaO质量分数降低,Al2O3质量分数升高;热力学计算表明,钙处理后钢液可直接生成CaS,也可与钙铝酸盐夹杂物反应生成CaS,RH破空后不能生成CaS。     

GCr15轴承钢RH和VD真空精炼过程钢洁净度对比

摘要：对比了RH和VD真空精炼工艺生产的GCr15轴承钢精炼过程的洁净度水平,研究了钢液中总氧（TO）、总氮（TN）、总硫（TS）以及夹杂物变化规律。轴承钢对洁净度要求较高,RH精炼工艺在降低钢中TO、TN含量,固相夹杂物去除,循环效率上均具有优势。经过RH精炼后,钢液中TO含量下降了61%,TN含量下降了15%,夹杂物数密度降低了75%;VD精炼过程中,钢渣反应剧烈,脱硫效果优异,VD精炼后钢液中TS含量下降了50%,但钢液循环速率远落后于RH精炼,且更容易发生卷渣。不同液相分数的夹杂物与钢液的接触角不同,液相分数小于27%的夹杂物与钢液不润湿,容易碰撞长大和上浮去除,而液态夹杂物黏附功更大,难以从钢液中去除。     

LF处理过程中钢水增铝问题的研究

硅镇静钢及少量铝脱氧的钢在LF处理过程中会发生钢水中铝含量增加以及夹杂物组成改变的现象.通过理论计算和工业生产实践研究了不同的渣系、钢水成分、处理时间等对LF精炼过程增铝的影响,不同精炼渣系下钢中夹杂的组成,结果表明采用CaO-SiO2渣系LF处理过程几乎不发生增铝现象,而采用CaO-Al2O3渣系随着处理时间的延长以及钢种成分的区别,钢中铝有不同程度的增加,生产实践结果与理论计算趋势基本一致.采用CaO-Al2O3渣系精炼与CaO-SiO2渣系相比,钢中Al2O3夹杂数增加4倍,氧化物复合夹杂中w(Al2O3)提高113%,w(CaO)提高24.5%.在帘线钢72A以及HRB400、SS400钢的生产实践中加以应用,使得LF处理后72A的w(Al)小于0.000 5%,HRB400、SS400的小于0.003%,避免了有害夹杂物的形成,消除了在小方坯连铸过程中的水口堵塞现象.     

Mathematical Modelling of Non‐equilibrium Decarburization Process during Vacuum Circulation Refining of Molten Steel: Application of the Model and Results (II) ‐ Non‐equilibrium Factors and their Influences on the Decarburization Process

The results, which were obtained by applying the novel three‐dimensional mathematical model proposed and developed earlier [1] to model and analyse the decarburization process of molten steel during the RH and RH‐KTB refining in a 90‐t multifunction RH degasser, showed that under the conditions of the present work, the contributions of the flow, mass diffusion and chemical reactions and other non‐equilibrium processes to the Raleigh‐Onsager dissipation function are not large throughout vacuum circulation refining of molten steel. Thus, it is held everywhere in the whole flow field of the system that the value of the non‐linear dissipation factor is approximately equal to one. The entropy generation and energy dissipation in the system rapidly decrease with increasing refining time. Compared to the work done by the drag force while the bubbles passing through the liquid phase as well as by the viscous and turbulent flow and diffusion processes, the carbon‐oxygen reaction itself plays a more governing role to the entropy production and energy dissipation in the system. The RH refining process of low and ultra‐low carbon steels seems to be close to the linear zone of the non‐equilibrium state. The influences of the viscous and turbulent flow dissipation as well as diffusion processes on the non‐equilibrium activity coefficients of the carbon and oxygen in the molten steel may almost be neglected. Except in the regions where the chemical C‐O reaction takes place (the up‐snorkel zone and the bath in the vacuum vessel), the non‐equilibrium components of the non‐equilibrium activity coefficients of the carbon and oxygen in the molten steel at the other places in the degasser are all tending towards one. The non‐equilibrium effects (mainly, the C‐O reaction itself) give a restraining role on the decarburization of liquid steel in the RH refining process. This model is able to model more reasonably and precisely the non‐equilibrium decarburization process during the vacuum circulation refining of molten steel in comparison to a model without considering the non‐equilibrium effects.