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.

Analysis of Coating Microstructure of Hot-Dip Aluminum of Deformed Low-Carbon Steel Containing Rare Earth

The coating microstructure of hot-dip aluminum (HDA) of deformed low-carbon steel containing RE was analyzed by metallography microscopy, TEM and XRD, and the forming mechanism was also discussed. The results show that, the Fe_2Al_5 phase, on whose subcrystal boundaries, Al particles with the size of 7～30 μm existing on parallel linear are, grows a strong orientation. And the spread activation energy of Al is 155.22 kJ·mol -1. In addition, the effects of deformation on coating microstructure of hot-dip aluminum and the function of RE were preliminarily analyzed.

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.

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.

连铸LCAK钢保护渣生产工艺优化及开发

在对国内外连铸结晶器保护渣特性综合分析的基础上，结合莱钢板坯铸机生产低碳铝镇静钢的具体条件，设计开发了用于低碳铝镇静钢的板坯连铸的结晶器保护渣。用热丝法观察了板坯连铸结晶器保护渣的析晶状况，未发现结晶析出。通过优化工艺参数，调整水分与粘合剂配比，采用喷雾干燥工艺生产出合适粒度分布和低水分含量的空心球形颗粒保护渣。工业试验表明，所研制保护渣能够满足莱钢08Al钢板坯连铸的生产要求，生产的连铸坯表面质量和内部质量合乎标准要求。

低碳铝镇静钢精炼渣理化性能研究及动态调控

为提升低碳铝镇静钢水的可浇性,基于低碳铝镇静钢精炼渣的热力学计算,研究典型组分CaO/Al2O3(C/A)、SiO_(2)、FeO对精炼渣液相线温度、1650℃黏度和表面张力的影响规律,结合精炼渣理化性能(熔点和黏度-温度曲线)测试结果,建立吹氩直上精炼渣动态调控模型,并投入生产实践应用。结果表明:随着C/A增加,精炼渣熔点在渣中SiO_(2)质量分数为5%时单调升高,在渣中SiO_(2)质量分数为10%时先降后升,另随C/A的增加精炼渣黏度及黏度-温度曲线的转折温度升高;精炼渣组分范围为C/A 0.75~1.50、SiO_(2)质量分数0~10%、FeO质量分数2%~6%时,可获得较低的液相线温度、较高的黏度和表面张力。生产实践中应用建立的模型可实现造渣物料的动态加入,精炼渣理化性能的稳定性得到显著提升,精炼渣的C/A和全铁(TFe)质量分数标准差明显降低;液相线温度、1650℃时的黏度和表面张力平均值分别降低6.9℃、增加0.0206 Pa·s和0.0109 N/m;全氧(TO)质量分数均值由2.78×10(-3)%下降为2.25×10(-3)%,改进了19.1%,钢水的可浇性得到显著改善。

90 t转炉冶炼低碳含铝钢脱氧合金化实践

针对90 t转炉冶炼低碳含铝钢时合金收得率低的问题,分析了影响合金收得率的主要原因,采取优化转炉终点钢水中的氧含量,优化复合脱氧合金配比,调整渣料组成并合理使用挡渣塞后,降低了脱氧铝的消耗,合金收得率提高至87.4%,整体合金成本降低7元/t以上。

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。

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.

A6061铝合金与Q235钢电阻点焊接头组织与性能

采用热补偿电阻点焊方法对A6061铝合金与Q235低碳钢进行焊接,探讨了焊接电流、电极压力对接头熔核尺寸和抗剪力的影响,观察分析了熔核界面区反应物形貌及分布等微观组织结构特征。试验结果表明,A6061铝合金与Q235低碳钢采用热补偿电阻点焊方法能在较低的焊接电流条件下获得具有较大熔核与较高抗剪力的点焊接头;接头熔核直径及抗剪力随焊接电流、电极压力的增大而增大;无飞溅条件下接头最大抗剪力为4.25 kN,对应的焊接电流为17.5 kA;接头界面处生成了主要由Fe2Al5和FeAl3构成的金属间化合物层。

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。

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。

铝锌硅热浸镀液的侵蚀性及镀层结构与性能研究

为了解热浸镀铝锌硅钢板的耐蚀机制,通过试验考察了普通低碳冷轧钢板在600℃的铝锌硅(55%Al43.4%Zn1.6%Si)热浸镀液中的失重减薄规律,利用扫描电镜及能谱仪对镀层的微观结构及微区成分进行了分析,并利用X射线物相分析技术对合金层进行了物相分析。结果表明:钢板在镀液中的质量损失与浸镀时间大致呈线性关系;镀层主要由富铝的树枝晶、树枝晶间的铝锌共晶、针状富硅相以及合金层4个部分组成,这种独特的结构决定了铝锌硅镀层钢板具有优良的防腐蚀、耐热性能。

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。

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。

酸溶铝含量对低碳铝镇静钢组织性能及织构的影响

通过单向拉伸试验机测量两组不同酸溶铝含量低碳铝镇静钢试样的力学性能,利用光学显微镜观察其显微组织,利用电子背散射衍射仪(EBSD)观察其微观织构情况。结果表明,酸溶铝含量为0.1%的实验钢,屈服强度和抗拉强度过高,分别为257和336 MPa,而塑性应变比为0.84,几乎失去了深冲性能,而各取向织构在冶金生产过程中没有明显的密度变化,退火后有利的{111}取向织构密度仍较低;而酸溶铝含量为0.021%的低碳铝镇静钢强度较低,屈服强度和抗拉强度分别为190和282 MPa,塑性应变比为1.19,性能较为优异,且有利织构在退火后明显增加,因此实验钢的适宜酸溶铝质量分数控制在0.021%左右。

冷轧压下率对低碳铝镇静钢板组织及力学性能的影响

通过单向拉伸试验检测试验钢力学性能,利用金相显微镜观察低碳铝镇静钢板冷轧态与退火态的纤维组织,并用X射线衍射仪测量试验钢中不同类型织构的含量。利用单机架可逆轧机轧制,冷轧压下率由52%升高到80%,低碳铝镇静钢的屈服强度为187～211 MPa,抗拉强度为284～294 MPa,屈强比为0.66～0.72,总伸长率为38%～43%,n值为0.23～0.24,而r值为1.13～1.36,|△r|值为0.39～0.65。结果表明,冷轧压下率的提高使得退火再结晶晶粒尺寸均匀细小,储存能增加,γ纤维织构充分形成和发展。当冷轧压下率达到一定程度时,{111}织构增强速度减弱,不利织构{100}组分增幅较大。综合作用的结果是,当冷轧压下率为68%时,r值出现峰值且|△r|值较小,深冲性能最好。