包晶反应产物侧向生长速度的研究

针对Fe-C合金包晶反应过程中,γ相沿L/δ界面侧向生长速度的实测值远远大于Bosze和Trivedi[2]模型的计算值的问题,分析了包晶反应过程中固/液界面前沿溶质浓度分布状况,得到了金属熔体中圆柱形固相生长时固/液界面前沿溶质浓度分布表达式.以Jackson[9]提出的熔体中粗糙界面生长速度公式为基础,确定了适合计...     

Stability of remelting and solidification interfaces of triple-phase region during peritectic reaction at lower speed

Peritectic reaction was studied by directional solidification of Cu-Ge alloys. A larger triple junction region of peritectic reaction was used to analyze the interface stability of the triple junction region during peritectic reaction. Under different growth conditions and compositions, different growth morphologies of triple junction region are presented. For the hypoperitectic Cu-13.5%Ge alloy, as the pulling velocity (v) increases from 2 to 5 μm/s, the morphological instability of the peritectic phase occurs during the peritectic reaction and the remelting interface of the primary phase is relatively stable. However, for the hyperperitectic Cu-15.6%Ge alloy with v=5 μm/s, the nonplanar remelting interface near the trijunction is presented. The morphological stabilities of the solidifying peritectic phase and the remelting primary phase are analyzed in terms of the constitutional undercooling criterion.     

包晶钢15CrMoG方坯表面缺陷分析与改进

针对包晶钢15CrMoG的200 mm×200 mm连铸坯存在表面凹陷及纵裂漏钢问题,对铸坯表面检查进行分析及试验对比。结果表明,结晶器铜管和保护渣传热不均及二冷强度低导致表面产生凹陷缺陷及漏钢问题。通过将结晶器铜管锥度从0.72%/m提到1.10%/m、保护渣碱度从0.72提到1.05、黏度从0.44 Pa·s提到0.74 Pa·s、熔化温度由1 170℃提高到1 191℃及二冷比水量从0.30 L/kg提高到0.45 L/kg等措施,改善结晶器冷却传热和二冷段喷淋冷却效果,提高铸坯冷却均匀性,使得铸坯缺陷明显改善。     

Unidirectional solidification of a Zn-rich Zn–2.17 wt%Cu hypo-peritectic alloy

Unidirectional solidification of a Zn-rich Zn-2.17 wt%Cu hypo-peritectic alloy has been carried out to investigate the microstructure evolution over the growth velocity range 0.02–4.82 mm/s ata temperature gradient of 15 K/mm by means of the Bridgman technique. Regular and plate–like two-phase cellular structures were observed in samples grown at growth velocities V above 0.48 and 2.64 mm/s,respectively. The dominant microstructure in samples grown below 0.22 mm/s was dendrites of primary sin a matrix of secondary η. Intercellular spacing ι decreased ε with increasing growth velocity V such that ιV¹² is a constant of 316 ± 55 µm^3/2/s^1/2. Secondary dendrite arm spacing λ₂ of primary decreased with increasing V such that λ₂V^1/3 isa constant of 14.9 ± 0.9 µm^4/3/s^1/3. The observed transition from regular cells to plate-like cells of η is discussed on the basis of competitive growth and crystallographic effect.     

板坯高拉速表面纵裂纹产生原因及解决措施

凌钢板坯连铸生产的钢种多为碳的质量分数0.08%～0.16%包晶钢,由于高拉速使弯月面热流增加,产生严重的表面裂纹。除优化连铸工艺、设备参数外,通过浸入式水口结构优化设计,并配合优良性能的保护渣,使结晶器流场均匀、温度场均匀、坯壳凝固均匀,使铸坯表面缺陷得到消除。     

Q345D低碳钢近平衡凝固相的转变试验

为了研究近平衡凝固对液相线和包晶反应温度的影响,分别采用差热分析仪和自制的高温相转变凝固试验装置对Q345D低碳钢进行凝固相转变试验及高温凝固组织进行研究。试验表明,试样在近平衡冷却条件下20和30 ℃/min冷却时,与平衡凝固相转变相比初生铁素体析出温度分别降低了56和88 ℃,包晶反应转变温度分别降低了29和68 ℃。另外,在液相线以上发生近平衡凝固后得到的组织为液相直接形成奥氏体;在包晶转变温度发生近平衡凝固时,形成奥氏体晶粒形核较小,晶内组织为针状马氏体,晶界处有少量高温自由铁素体,包晶反应未发生;而在奥氏体转变区发生近平衡凝固时,奥氏体晶粒充分长大,即包晶反应转变完全发生,同时高温铁素体消失。     

包晶钢连铸用保护渣性能优化

针对包晶钢的凝固特点,分析了浇注包晶钢用保护渣应具备的理化性能,并结合国内某厂情况,优化了其连铸用保护渣的理化性能,现场使用效果良好,能够为浇注包晶钢合理选择保护渣提供理论指导。结果表明,该钢种保护渣应具有合理的粘度、液渣层厚度〉10 mm、较高的结晶温度和适宜的熔化温度及熔速。     

Nd-Fe-B包晶合金定向凝固组织的研究

利用亚快速定向凝固设备制备Nd-Fe-B合金,并研究了其定向凝固组织.设计合金成分为:亚包晶成分(Nd10.8Fe83.8B5.4)、包晶成分(Nd11.76Fe82.36B5.88)和过包晶成分(Nd13.5Fe79.75B6.75).对抽拉速率在5～500μm/s范围内合金的定向凝固及微观组织的研究表明:三种成分Nd-Fe-B合金的最终凝固组织均由α-Fe枝晶相、包晶Nd2Fe14B相和富Nd相组成;随着抽拉速率的提高,α-Fe相的一次枝晶间距呈减小的趋势;三种成分凝固组织中的α-Fe相的体积分数随着抽拉速率的提高都表现出了先减后增的趋势,而Nd2Fe14B相的体积分数都表现出了先增后减的趋势.     

高温超导YBCO的定向凝固

讨论了YBCO高温超导体定向凝固中所涉及的包晶反应、界面稳定性及其形态控制、凝固取向和晶向控制等问题。并提出了定向凝固中应该注意的问题。     

Ti-(44-50)Al合金定向包晶凝固过程中的组织演化

利用TiAl二元系的热力学模型,计算了Ti—(44—50)Al(原子分数,％)合金包晶反应附近的相图,确定了初生相β和包晶相α的固、液相线,得到了界面响应函数所需的部分参数．利用这些参数及单相合金凝固界面响应函数模型,计算了初生相β和包晶相α的界面温度与生长条件变化的关系;结合最高界面生长温度判据,分析了Ti—(44—50)Al合金凝固过程中的相选择和组织演化,并确定了Ti—Al合金稳态凝固时以成分和G／υ为框架的相选择图．