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Dissolution Kinetics of Iron-Based Intermetallic Compounds (τ5c IMCs) in a Commercial Steel Strip Metallic Alloy Coating Process
Metallurgical and Materials Transactions B ( IF 3 ) Pub Date : 2020-10-27 , DOI: 10.1007/s11663-020-01985-8
Abdul Khaliq , Daniel J. Parker , Nega Setargew , Katsuyoshi Kondoh , Ma Qian

The precipitation of discrete iron-based intermetallic compounds (τ5c IMCs) is an inevitable phenomenon in a steel strip coating pot due to the dissolution of iron from the steel strip surface and temperature perturbations in the pot. These τ5c IMC particles are a primary source of coating inclusions and bottom dross buildup in the coating pot. It has been hypothesized that they will re-dissolve into the pot during the heating cycle in the coating bath, but their dissolution kinetics remains largely unexplored. In this study, three forms of τ5c IMCs were used to investigate their dissolution kinetics: (i) τ5c-IMC disk samples (diameter: 14.88 mm) fabricated using a special approach; (ii) large τ5c IMCs (size: 1 to 10 mm) in the form of industrial mushy bottom dross (MBD); and (iii) fine suspended in-melt τ5c IMCs (size: < 50 μm). The driving force for dissolution is dictated by both the pre-existing iron content in solution in the AM alloy melt and the melt temperature. Experiments suggest that the dissolution kinetics of the τ5c IMCs in the forms of both τ5c-IMC disk and MBD is extremely slow (negligible) in the coating alloy at 595 °C. A mass transfer coefficient (km) of 1.43 × 10−6 m/s is calculated in an iron-unsaturated AM alloy bath at 595 °C. Re-dissolution of fine suspended in-melt τ5c IMC particles (< 50 μm) occurs at the stirring rate of 220 mm/s and their dissolution rate is much faster than that of either the τ5c-IMC disk samples or the mushy bottom dross τ5c IMC particles. However, overall, their dissolution kinetics is still very slow so that their contribution as a source of Fe is practically negligible, considering that the heating time interval during a temperature perturbation cycle in an industrial coating pot is only about 7.5 minutes. This clarifies a long-standing unanswered important issue to the steel strip alloy coating process. Consequently, coating bath temperature control is important in minimizing the precipitation and growth of τ5c IMC particles in an industrial steel strip coating process, in addition to managing the source of iron from the highly active surface-deoxidized moving steel strip.

中文翻译:

商业钢带金属合金涂层工艺中铁基金属间化合物 (τ5c IMC) 的溶解动力学

由于铁从钢带表面溶解和锅中的温度扰动,离散铁基金属间化合物(τ5c IMCs)的沉淀是钢带涂层锅中不可避免的现象。这些 τ5c IMC 颗粒是涂层内含物和底渣堆积的主要来源。据推测,它们将在镀液加热循环期间重新溶解到锅中,但它们的溶解动力学在很大程度上仍未得到探索。在这项研究中,三种形式的 τ5c IMC 用于研究它们的溶解动力学:(i)使用特殊方法制造的 τ5c-IMC 圆盘样品(直径:14.88 毫米);(ii) 工业糊状底渣 (MBD) 形式的大型 τ5c IMC(尺寸:1 至 10 毫米);(iii) 细悬浮熔体 τ5c IMC(尺寸:< 50 μm)。溶解的驱动力取决于 AM 合金熔体中溶液中预先存在的铁含量和熔体温度。实验表明,τ5c-IMC 盘和 MBD 形式的 τ5c IMC 在 595°C 时在涂层合金中的溶解动力学非常缓慢(可以忽略不计)。1.43 × 10−6 m/s 的传质系数 (km) 在 595 °C 的铁不饱和 AM 合金浴中计算得出。细悬浮熔体 τ5c IMC 颗粒(< 50 μm)的再溶解发生在 220 mm/s 的搅拌速率下,它们的溶解速率比 τ5c-IMC 圆盘样品或糊状底部浮渣 τ5c 快得多IMC 颗粒。然而,总体而言,它们的溶解动力学仍然非常缓慢,因此它们作为 Fe 来源的贡献实际上可以忽略不计,考虑到工业涂装锅在一个温度扰动循环中的加热时间间隔仅为7.5分钟左右。这澄清了钢带合金涂层工艺中一个长期悬而未决的重要问题。因此,除了管理来自高活性表面脱氧移动钢带的铁源之外,镀浴温度控制对于最大限度地减少工业钢带涂层过程中 τ5c IMC 颗粒的沉淀和生长非常重要。
更新日期:2020-10-27
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