共查询到18条相似文献,搜索用时 203 毫秒
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本文研究了在3种钢凝固过程中,化学成分、碳和锰含量以及冷却速率对凝固模式和相演变的影响,其中两个是亚包晶组成,另外一个是过包晶组成。并且推断了与裂纹敏感性有关的δ相和γ相力学性能差别以及凝固过程中的收缩。
碳或锰的轻微变化,当其变化数量级达到0.04%时,即可促进凝固过程中相演变的明显变化。试验观察到亚包晶钢接近包晶点,当冷却速率较高时可观察到锰的微观偏析,而且在凝固末端时,较高的冷却速率可促进过包晶凝固模式的发生。另一方面,凝固模式和所研究钢种的化学成分与裂纹敏感性无关,δ相和γ相力学性能差是导致两个固相分数区裂纹敏感性的原因。
而且与发生过包晶钢凝固模式的钢相比,对于亚包晶凝固模式的钢来说,包晶转变发生在固相分数较高区。因此,残留的液相能够补充包晶转变发生时固一液坯壳的收缩。所以在亚包晶钢中不仅可观察到由δ相和γ相力学性能差产生的裂纹敏感性,而且还可观察到液体不能补充与包晶转变有关的收缩。 相似文献
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针对亚包晶钢板坯连铸结晶器内经常出现的严重液面波动问题,从机制认识出发,进行了工艺试验研究。指出液面驻波和二冷区坯壳的非稳定鼓肚是导致结晶器液面波动的主要因素。通过调整亚包晶钢的化学成分,使其碳含量与实际包晶点的计算值接近,并适度增加二冷前区的冷却强度,可有效抑制液面波动。结果表明,亚包晶钢连铸突出的液面波动是因为其不均匀坯壳生长所造成的非稳定鼓肚。亚包晶钢实际碳含量距包晶点越近,相变收缩比例越小,坯壳厚度不均匀度以及后续坯壳非稳定鼓肚量的变化也将越小,有助于减小液面波动程度。 相似文献
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连铸过程中铸坯表面常产生各种质量问题,严重影响铸坯质量和生产顺行,然而,钢种初始凝固模式的差异对铸坯表面质量缺陷的影响规律尚不够明确。选用一系列代表性钢种,利用JmatPro软件进行了热力学平衡相图和高温力学性能的计算,结合Fe-C-X多元伪平衡相图特征点的理论计算公式,综合研究不同钢种的初始凝固模式及其对铸坯表面质量的影响规律。结果表明,对4种不同凝固模式的钢种而言,低碳、亚包晶凝固模式的钢种铸坯的主要表面质量缺陷分别是皮下夹杂、表面纵裂,其主要原因是高温阶段的相变引起的极限屈服强度和相变应变的变化;过包晶与高碳凝固模式的钢种铸坯很少出现表面质量问题。因此,表面缺陷的发生概率由钢发生高温相变(L+δ→γ/δ→γ)时δ相的比例、温度区间及坯壳的相变应变程度共同决定。基于钢种凝固模式及其对铸坯表面质量的影响,预测可能出现的铸坯表面质量缺陷,并采取相关措施降低表面缺陷发生率,对提高连铸坯质量具有重要意义。 相似文献
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分析得出,棒材表面细小纵裂纹和表面裂口缺陷产生于铸坯加热之前,且与结晶器弯月面保护渣有关。利用Thermo-Calc热力学软件计算15CrMoG钢凝固相变过程,结合亚包晶钢连铸凝固特点综合分析15CrMoG钢棒材表面缺陷的产生原因和产生机理。结果表明:15CrMoG钢在固相线温度附近发生包晶反应L+δ→γ和包晶转变δ→γ,不仅导致初生坯壳生长不均匀,而且加剧P、S元素在凝固前沿的偏析。而初生坯壳不均匀是导致棒材表面缺陷根本原因。棒材表面细小纵裂纹产生于结晶器内坯壳薄弱处,经过二冷和轧制工序在夹杂物和硫偏聚处扩展长大。棒材表面裂口缺陷是初生坯壳不均匀导致结晶器内液面波动大,造成铸坯夹渣所致。通过控制[C]0.16%~0.17%、[S]≤0.005%、保护渣碱度1.2、熔点≥1200℃、粘度≥1.0Pa·s,260 mm×30mm铸坯水量150 m3/h,拉速0.5 m/min等措施,裂纹合格探伤合格率由原45%提高至98%。 相似文献
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本文描述了亚包晶钢在连续冷却条件下,凝固过程中的相转变。此外,通过采用文献中报道的数学表达式,评价了固一液相区的力学性能和空间变化,该数学表达式为相和溶质分布的比例函数。固-液相区的裂纹敏感性取决于相的比例,并且其发生在两个固相分数范围区,与冷却速率无关。对于具有最低固相分数值的区域,这种裂纹敏感性与γ相有关,而在最高固相分数值区域,则与8相有关。在包晶转变结束时,可观察到最高的相区收缩,考虑是由于在固相分数值介于0.92—0.98范围时,出现了裂纹敏感区。在高冷却速率条件下,可观察到明显的锰显微偏析,因为在高冷却速率条件下,促进了凝固模式的变化,从亚包晶模式进入到过包晶模式,并且促进从残余液相中形成固相区的扩张变化。 相似文献
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In continuous casting of peritectic steel grades sensitive to longitudinal cracking, the solidification properties of mold fluxes play an important role in keeping smooth running of continuous casting process and achieving high surface quality of casting strands. To reduce fluorine pollution in molten slag, types of CaO-SiO2-TiO2 (CTS) based mold fluxes were investigated. The solidification and crystallization properties, including viscosity η at 1573 K, break temperature Tbr, crystallization ratio Rc and solidification mineragraphy were measured, which were compared with those of CaO-SiO2-CaF2 based mold fluxes. The experiments show that there are unstable viscosity-high temperature properties and high Tbr in part of CTS slag system, which are bad for lubrication between liquid flux film and strand. And when temperature is below Tbr, the viscosities change slowly during cooling in some part of this slag system, which imply that liquid mold fluxes solidify slowly and it is easy to cause surface longitudinal cracks on strand. Major mineragraphy of the CaO-SiO2-TiO2 based mold fluxes are CaO·TiO2 or CaO·TiO2 and CaO·SiO2·TiO2. TiN and Ti(C,N) can be formed in mold fluxes bearing high TiO2 during the continuous casting. 相似文献
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In high speed continuous casting of peritectic steel slabs, mold fluxes with high basicity are required for less surface defect product. However, the basicity of remaining liquid slag film tends to decrease in casting process because of the crystallization of 3CaO·2SiO2·CaF2. Thus, a way is put forward to improve mold fluxes′ properties by raising the original basicity. In order to confirm the possibility of this method, the effect of rising original basicity on the properties of mold fluxes is discussed. Properties of high fluorine based mold fluxes with different basicities and contents of CaF2, Na2O, and MgO were measured, respectively. Then, properties of higher basicity mold fluxes were discussed and compared with traditional ones. The results show that increasing the basicity index can improve the melting and flow property of mold fluxes. With the increasing basicity, crystallization rate of mold fluxes increases obviously and crystallization temperature tends to decrease when the basicity exceeds 1.35. The method presented before is proved as a potential way to resolve the contradiction between horizontal heat transfer controlling and solidified shell lubricating for peritectic steel slab casting. But further study on improving the flow property of liquid slag is needed. This work can be used to guide mold fluxes design for high speed continuous casting of peritectic steel slabs. 相似文献
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ZHU Miaoyong CAI Zhaozhen School of Materials Metallurgy Northeastern University Shenyang China 《Baosteel Technical Research》2010,(Z1):26
Thermal behavior of the solidifying shell in continuous casting mold is very important to final steel products.In the present work,one two-dimension transient thermal-mechanical finite element model was developed to simulate the thermal behavior of peritectic steel solidifying in slab continuous casting mold by using the sequential coupling method.In this model,the steel physical properties at high temperature was gotten from the micro-segregation model withδ/γtransformation in mushy zone,and the heat flux was obtained according to the displacement between the surface of solidifying shell and the hot face of mold as solidification contraction,the liquid-solid structure and distribution of mold flux,and the temperature distribution of slab surface and mold hot face,in addition,the rate-dependent elastic-viscoplastic constitutive equation was applied to account for the evolution of shell stress in the mold.With this model,the variation characteristics of surface temperature,heat flux, and growth of the solidifying shell corner,as well as the thickness distribution of the liquid flux,solidified flux,air gap and the corresponding thermal resistance were described. 相似文献
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针对攀钢连铸 Q2 35 G等包晶钢生产中出现的铸坯表面裂纹问题 ,在调查分析裂纹特征及其产生原因的基础上 ,发现保护渣传热过强和保护渣流入不均是诱发角横裂产生的主要原因。通过对保护渣结晶特性的研究 ,开发出了低碱度 (Ca O/ Si O2 <1.0 )、高结晶率的新型包晶钢用连铸保护渣。工业试验表明 ,研制的保护渣具有良好的使用效果 ,所浇铸坯表面质量优良 ,铸坯裂纹较少 ,表面角横裂发生率降低到 4 .19% ,纵裂发生率为 3.4 2 % ,且保护渣润滑作用良好 ,未发生漏钢事故。 相似文献
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从分析高拉速包晶钢板坯连铸结晶器内凝固传热行为特征入手,首先阐明拉速对结晶器内的界面热阻、凝固坯壳的温度与应力分布的影响规律,研究发现拉速超过1.6 m·min?1时,界面热阻明显增加,拉速由1.4 m·min?1提升至1.6 m·min?1和1.8m·min?1时,出结晶器坯壳厚度相应减少约10%,其发生漏钢的危险不断增加;在此基础上,阐述了结晶器的内腔结构、保护渣、振动与液面控制等控制结晶器内坯壳凝固均匀性的相关技术。要实现高速连铸,首要应考虑结晶器内腔结构的优化设计,使其能更好地迎合凝固坯壳的生长,研制适合包晶钢等凝固特点的专用连铸保护渣至关重要,铸坯鼓肚控制也是保障高拉速液面稳定的关键。 相似文献
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为了控制梅钢1 650板坯连铸包晶钢过程铸坯内裂纹发生,基于梅钢1 650板坯连铸机生产实际,建立了1 560mm×230mm断面包晶钢铸坯凝固过程三维热/力耦合有限元模型,揭示了铸坯凝固过程各冷却区内的温度场分布规律和铸坯压下过程应力与变形行为演变规律。结果表明,铸坯在结晶器及零段内冷却强度大,沿拉坯及其垂直方向的温度分布梯度大;在实施铸坯凝固末端压下过程中,铸坯宽面中心与宽向1/4处的表面变形及应力变化较为同步,且靠近铸坯内弧侧凝固前沿的塑性应变最大,铸坯应力最大值集中在角部区域;目前梅钢包晶钢连铸压下区间设置不当,易引发铸坯产生内部裂纹。 相似文献