Control of Ultra Low Titanium in Ultra Low Carbon Al-Si Killed Steel

Titanium is the impurity in some special steel grades.The existence of titanium decreases the grain size,depresses the yield strength,and results in the low quality of these steels in various properties.Thus,titanium should be removed to the minimum.Based on the industrial production of ultra low carbon Al-Si killed steel,the physical-chemical behavior of titanium was investigated in vacuum degassing refining（RH）process with and without desulfurization.The influences of titanium content in hot metal,ladle slag composition,and ladle slag quantity,etc,on titanium content of refined liquid steel were discussed.The results showed that the partition ratio of titanium between ladle slag and liquid steel is in inverse proportion to the 4/3square of aluminum content.The maximum partition ratio of titanium between top slag and liquid steel can be obtained by adjusting an optimum slag composition including contents of FeOxand Al2O3and the slag basicity,and the suitable range of them should be controlled higher than 6%,less than 20%,and within 1.5to 3.0,respectively.Moreover,desulfurization refining by RH decreases the partition ratio of titanium between ladle slag and liquid steel significantly.To ensure the titanium content stably less than 15×10-6 in a 300tladle,the titanium content in hot metal must be less than 500×10-6 and the thickness of basic oxygen furnace（BOF）slag carrying over must be less than 50mm.

Novel mechanism for the modification of Al_2O_3-based inclusions in ultra-low carbon Al-killed steel considering the effects of magnesium and calcium

Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid steel were conducted using ultra-low-carbon Al-killed steel with different Mg and Ca contents to verify the effects of Ca and Mg contents on the modification mechanism of Al_2O_3-based inclusions during secondary refining. The results showed that Al_2O_3-based inclusions can be modified into liquid calcium aluminate or a multi-component inclusion with the addition of a suitable amount of Ca. In addition, [Mg] in liquid steel can further reduce CaO in liquid calcium aluminate to drive its evolution into CaO–MgO–Al_2O_3 multi-component inclusions. Thermodynamic analysis confirmed that the reaction between [Mg] and CaO in liquid calcium aluminate occurs when the MgO content of liquid calcium aluminate is less than 3 wt% and the temperature is higher than 1843 K.

Subsurface macro-inclusions and solidified hook character in aluminum-killed deep-drawing steel slabs

Subsurface macro-inclusions and hooks are detrimental to the surface quality of deep-drawing steel sheets. However, little is known about the relationship between macro-inclusions and hooks. Thus, in this work, two ultralow carbon （ULC） steel slabs and two low carbon （LC） aluminum-killed steel slabs were sampled to study the relationship between hooks and subsurface macro-inclusions, which were detected on the cross-sections of steel samples with an area of 56058 mm2 using an automated scanning electron microscopy/energy-disper-sive X-ray spectroscopy system. Results show that subsurface inclusions larger than 200 μm were almost entrapped by hook structures, whereas the location of other inclusions smaller than 200μm had no obvious dependence on the location of solidified hooks. Furthermore, the number density （ND） of subsurface inclusions larger than 200μm decreased from 0.02 to 0 cm-2 in ULC steel as the mean hook depth decreased from 1.57 to 1.01 mm. Similar trends were also observed in LC steel. In addition, the detected inclusions larger than 200μm were concentrated in the region near the slab center （3/8 width-5/8 width）, where hook depths were also larger than those at any other locations. Therefore, minimizing the hook depth is an effective way to reduce inclusion-induced sliver defects in deep-drawing steels.

低碳铝镇静钢汽车板磷化性能及改善对策研究

为解决低碳铝镇静钢汽车板在磷化工艺下限条件下磷化膜结晶粗大及覆盖率不足问题,采用扫描电镜(SEM)、表面轮廓仪、辉光光谱仪(GDS)及透射电镜(TEM)研究了低碳铝镇静钢汽车板磷化性能关键影响因素,并提出了改善对策。结果表明:当磷化工艺处于下限条件即促进剂浓度、总酸浓度较小,而游离酸浓度较大时,钢板与磷化液界面磷酸盐不易饱和,磷化形核难度加大,导致磷化结晶粗大及覆盖率不足等问题。但当钢板表面存在均匀分布且数量较多的小尺寸氧化物颗粒时,氧化物与铁基体能够形成大量原电池,提升局部磷化酸蚀及沉积反应速度,进而改善磷化性能。通过对低碳铝镇静钢碳含量及退火快冷段、过时效段温度进行控制,成功在钢板表面析出尺寸较小且均分分布的碳化物。由于碳化物与铁基体之间存在电位差,同样增加了钢板表面原电池数量,促进了磷化形核,所获得的磷化膜晶粒尺寸在5μm以下,覆盖率为100%。

镀锌家电板DX51D+Z冲压橘皮的原因分析及工艺优化

针对DX51D+Z低碳铝镇静钢镀锌家电板冲压橘皮问题,分别从化学成分、热轧工艺、冷轧镀锌工艺等进行对比分析。结果表明,镀锌板冲压橘皮缺陷受时效的影响,均与固溶碳原子的存在相关;热轧卷取温度、镀锌均热温度及光整延伸率对固溶碳原子引起的时效具有重要影响,降低固溶C和N含量、保证热轧卷取温度、镀锌均热温度精准控制及光整延伸率稳定控制可有效改善橘皮缺陷。

Analysis of thermodynamics and kinetics of titanium between top slag and liquid steel

Titanium is an impurity element in some special steel grades. The existence of titanium decreases the grain size and lowers the yield strength ,resulting in low quality of these steels with regard to various properties. Thus, the titanium content should be reduced to the minimum. Based on the industrial production of ultra-low carbon A1-Si killed steel, this paper investigated the physical-chemical behaviors of titanium with and without desulfurization during RH refining. The influences of Ti content in hot metal, ladle slag composition, and ladle slag quantity, etc., on the Ti content in refined liquid steel were discussed. The results show that the partition ratio of titanium between ladle slag and liquid steel is inversely proportional to the AI content to the power of 4/3 ,and the empirical formula regressed from practical experience can be expressed as w（TiO2）/Wti=48/w[AI]4/3 Maximum partition ratio of titanium between top slag and liquid steel can be ensured W[Til WIAIIby an optimum slag composition including components of FeOx and A12 03 and an appropriate slag basicity. The contents of FetO and A1203 should be controlled above 6% and below 20% respectively and the slag basicity should be kept within 1.5 to 3.0. Moreover, desulfurization refining in the RH vacuum will decrease the partition ratio of titanium between ladle slag and liquid steel significantly. To keep the Ti content stably below 15 ×10 ^-4% in a 300 ton ladle ,the Ti content in hot metal must be lower than 500 × 10^-4% and the thickness of ladle slag carried over from BOF slag must be less than 50 ram.

强制冷却工艺对低碳铝镇静钢组织和性能的影响

采用强制冷却工艺可以加快热卷流转,提高生产效率。通过分析低碳铝镇静钢热轧态显微组织及力学性能,对比研究了不同冷却工艺对钢的组织及通卷性能的影响。结果表明,与自然冷却相比,强制冷却工艺的晶粒度相对均匀,两者的析出物都很少;强制冷却工艺的强度有一定提升,(550±30)℃入水工艺的屈服强度比自然冷却工艺平均高30 MPa左右。同时,通卷的性能均匀性也有效改善,选用入水温度为(400±30)℃的水冷工艺能保证合适的强度且通卷性能差异控制在20 MPa以内。

转炉出钢顶渣优先脱氧工艺研究

某钢厂在低碳铝镇静钢生产实践中,摸索出一种利用出钢过程良好动力学条件,配合使用特殊物性的铝钙脱氧造渣剂(以下简称铝钙合金),在出钢至进氩站钢水高氧势状态下,将“白渣”前置到出钢过程的新型顶渣改质和脱氧造渣工艺。该工艺在降低铝耗的同时,能够大幅提升钢水纯净度,为后续炉外精炼工艺的高效实施创造了优先条件。

Microstructure and texture evolution during recrystallization of low-carbon steel sheets

Aluminum killed low-carbon steel sheets were cold rolled at different reduction ratios and annealed using different temperatures and holding time.The Vickers hardness was examined.The results show that when cold rolling reduction ratios increase from 40% to 81%,recrystallization temperatures decrease from 602℃ to 572℃ during 4hisochronal annealing,as well recrystallization holding time decreases from 117 min to 5min during isothermal annealing at 610℃.All recrystallization temperatures and holding time can be calculated using the annealing experiment results.Microstructure was examined through electron backscattered diffraction（EBSD）.The results show that as rolling direction preferentially grows,equiaxed grains grow into cake-type during recrystallization.Cake-type grains are more beneficial to obtaining ideal〈111〉//ND（normal direcrtion）orientation texture.{111}orientation grains nucleate and grow up preferentially.Deformation grains of{111}〈110〉orientations grow into new recrystallization grains of{111}〈123〉and{111}〈112〉during recrystallization.Texture formation can be explained by directional nucleation.

终轧温度和卷取温度对低碳铝镇静钢性能的影响

通过现场试验和实验室检验，研究了终轧温度和卷取温度对低碳铝镇静钢性能的影响。结果表明，热轧过程中终轧温度偏低，导致低碳铝镇静钢热轧商品卷延伸率偏低，延伸率与卷取温度关系不大，但冷轧成品的性能与终轧温度和卷取温度却密切相关。

中间包塞棒吹氩技术的应用

通过对堵塞水口及堵塞物形态的调查，分析了引起水口堵塞的主要原因，并采用了中间包塞棒吹氩技术来预防水口堵塞。工业实验表明，该技术不仅能有效地防止水口堵塞，增加低碳铝镇静钢的连浇炉数。

薄板坯连铸连轧低碳铝镇静钢中酸溶铝的作用研究

对薄板坯连铸连轧低碳铝镇静钢中酸溶铝的作用进行了研究。研究结果显示，对于薄板坯连铸连轧流程生产的低碳铝镇静钢，当钢中酸溶铝的质量分数在0．005％～0．043％时，酸溶铝对热轧板材的晶粒度及力学性能没有明显影响，但是对热轧板材再加热时的晶粒长大却有明显影响，随钢中酸溶铝含量的增加，钢的晶粒粗化温度不断提高。因此对于那些不需要强调焊接性能的普通热轧钢板，w（Als）可以控制在0．01％左右；对于那些需要强调焊接性能和某些特殊性能的钢板将w（Als）控制在0．02％～0．04％比较合适。

退火工艺对冷轧深冲板组织和性能的影响

Under the laboratory conditions,the recrystallization temperature of P08AI deep drawing sheet steel was determined,and effects of both heating rate between 500℃ and 710℃ during batch annealing and holding time at 710℃ on microstructures,properties and recrystallization textures were investigated. Annealing conditions beneficial to improve drawing properties of 08Al sheet steel were further put forward.

冷轧压下率对低碳铝镇静钢冷轧板深冲性能的影响

采用攀钢热轧板厂生产的低碳铝镇静钢热轧卷 ,在实验室进行了不同压下率对冷轧钢板深冲性能的影响试验。结果表明 ,冷轧压下率对常规力学性能和n值无明显影响 ,而对r值影响显著。对于含碳量 0 0 59%的低碳铝镇静钢 ,获得最大 r值的冷轧压下率为 73% ,而Δr值随冷轧压下率的提高单调减小。

转炉-连铸工序生产低碳铝镇静钢中夹杂物的研究

采用添加示踪剂的方法对转炉—CAS—连铸工艺生产低碳铝镇静钢中的夹杂物进行了研究 ,结果表明 :出钢或CAS精炼过程中炉渣与钢液作用生成的夹杂物 ,尺寸在 3 0 μm以下的夹杂物很难从钢液中完全上浮排出。铸坯中的主要夹杂物为来源于钢包渣与钢液作用生成的球状夹杂物、块状Al2 O3 夹杂物。连铸坯中的全氧含量在 ( 3 8～ 5 3 )× 10 -6之间 ,夹杂物的含量在2 .3mg/kg左右 。

低碳铝镇静钢冷轧板中孔洞缺陷特征分析

对生产中常见的低碳铝镇静钢冷轧板孔洞缺陷特征进行了宏观和微观分析。结果表明 :孔洞大致可分为三大类 ,正常拉裂类孔洞主要与基板中的夹杂有关 ;疤块孔洞与坑状孔洞为钢基掉块或异物压入基板形成 ,其它类孔洞形成主要与轧制工艺过程相关。

低碳铝镇静钢铝锰铁脱氧合金化试验

介绍了攀钢用铝锰铁脱氧合金化生产高级别冷轧薄板用钢的可行性和脱氧合金化生产低碳铝镇静钢的工艺路线。采用铝锰铁脱氧合金化后 ,低碳铝镇静钢的炼成率从现工艺的 85 %提高到 99%以上 ,并且冷轧薄板的表面质量有了大幅度的提高。

二相粒子对低碳铝镇静钢织构演变规律的影响

通过单向拉伸实验检测力学性能,利用透射电镜观察化学成分不同的两种低碳铝镇静钢的析出相粒子,利用X射线衍射仪测量钢中各种织构的含量。经73%的压下率冷轧和700℃×4h退火处理,2#试样比1#试样屈服强度高28MPa,抗拉强度高19MPa,r值低0.24。结果表明:1#试样的{111}织构含量在冷轧、退火过程中都增加,Goss织构含量都减少,{100}织构含量冷轧后增加,退火后又明显减少;2#试样退火过程中析出大量Al2O3粒子抑制AlN粒子的析出,且其作为新的形核质点改变了形核机制,退火后Goss织构和{100}织构含量增加,而{111}织构含量减少,r值降低,不利于深冲性能;细小的Al2O3粒子的析出形成了细晶强化和沉淀强化,试样的屈服强度和抗拉强度都明显升高。

不同压下率低碳铝镇静钢板再结晶实验研究

将不同冷轧压下率的低碳铝镇静钢进行不同保温温度和时间的退火再结晶实验研究,利用维氏硬度计、金相显微镜和X射线衍射仪研究了退火后试样的硬度、金相显微组织及织构的变化情况。结果表明:在相同的退火工艺制度条件下,随着冷轧压下率的增加,再结晶开始和结束温度降低,晶粒尺寸减小。当冷轧压下率升高到68%后,冷轧压下率的增加对再结晶晶粒细化的作用减弱,甚至没有细化作用;680℃保温退火时,一开始就发生了再结晶,基本不需要孕育期。随着保温时间的延长,晶粒均匀长大,晶粒饼形程度增加;退火温度由660℃升高到720℃时,{111}面有利织构增加,{100}面不利织构减少,720℃退火温度较为适宜。冷轧压下率为58%的试样在760℃退火时发生了二次再结晶对实验钢板的力学性能产生不利影响。

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。