首钢SWRH82B线材异常组织成因分析

 首钢第一线材厂在生产SWRH82B线材过程中,盘条检测芯部出现异常组织现象：珠光体与残余奥氏体共存、索氏体与网状铁素体共存、索氏体与马氏体共存。通过对生产数据跟踪和扫描电镜观测发现,在冶炼、连铸过程中不稳定操作,铸坯中溶质元素碳、锰和铬元素偏析,钢液铬合金元素熔解不均匀,碳、锰和铬综合作用明显提高奥氏体的稳定性,大大推迟了奥氏体向珠光体的转变时间,在A1～Acm温度之间时间相对较长,形成残余奥氏体组织和珠光体、索氏体共存的局面;钢中溶质元素富集造成吐丝温度与相变之前冷速过快,形成片层间距不同的屈氏体和马氏体快冷低温组织。     

Improved methods for decreasing stresses of concrete slab of large-span through tied-arch composite bridge

Mechanical behavior of concrete slab of large-span through tied-arch composite bridge was investigated by finite element analysis (FEA). Improved methods to decrease concrete stresses were discussed based on comparisons of different deck schemes, construction sequences and measures, and ratios of reinforcement. The results show that the mechanical behavior of concrete slab gets worse with the increase of composite regions between steel beams and concrete slab. The deck scheme with the minimum composite region is recommended on condition that both strength and stiffness of the bridge meet design demands under service loads. Adopting in-situ-place construction method, concrete is suggested to be cast after removing the full-supported frameworks under the bridge. Thus, the axial tensile force of concrete slab caused by the first stage dead load is eliminated. Preloading the bridge before concrete casting and removing the load after the concrete reaching its design strength, the stresses of concrete slab caused by the second stage dead load and live load are further reduced or even eliminated. At last, with a high ratio of reinforcement more than 3%, the concrete stresses decrease obviously.     

一种配电变压器雷击特性仿真模型

在基于ATP-EMTP软件的仿真计算中,通常用来模拟配电变压器的变比模型并不能很好地表征雷电过电压在配电变压器绕组中的正、反变换过程。针对这一问题,提出一种基于ATP-EMTP软件的配电变压器集中参数雷击特性仿真等效模型。通过试验和计算求取模型中电容、电感、电阻参数,并采用算例仿真分析四点共地接线方式下配电变压器的正、反变换过电压,仿真结果合理。该模型建模较简单,适用于配电变压器建模,能够广泛应用于10 kV中压架空线路和设备的雷击特性计算,模拟雷电过电压在配电变压器绕组中的正、反变换过程,提高计算的准确性。