Development of X60/X70 Line Pipe Steels through EAF-Thin Slab Casting Technology at Ezz Flat Steel, Ain Sukhna, Egypt
Development of X60/X70 Line Pipe Steels through EAF-Thin Slab Casting Technology at Ezz Flat Steel, Ain Sukhna, Egypt
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埃及艾因苏赫纳的 Ezz Flat Steel 通过 EAF 薄板坯连铸技术开发 X60/X70 管线钢
DOI：
10.4028/www.scientific.net/msf.500-501.261
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
F. Ibrahim
中科院分区：
文献类型：
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作者：
G. Megahed;S. K. Paul;T. El;F. Ibrahim
API X60/X70管线钢具有较高的强度和优异的韧性，这是通过添加微合金化元素和控制轧制来细化晶粒而实现的。铌微合金钢薄板坯连铸生产过程中可能出现横向裂纹，这对钢铁生产企业是一个巨大的挑战。对影响横向裂纹的主要铸造参数进行了严格的检查和修改，以生产无缺陷板坯。还设计了热连轧机参数，用于板坯的控制轧制，以获得所需的机械性能。每175吨液态钢制造三炉（一炉X60和两炉X70），并加工成6、8和10 mm热轧卷。在X60炉次中，使用Nb和Ti作为微合金化元素，其中在X70炉次中还添加钒以实现所需的强度。通过控制Si和Mn的量，将YS/UTS比设计为低于0.9。在板坯连铸过程中，采用液芯压下（LCR）将板坯厚度从90 mm减小到70 mm，并使中心线偏析和气孔最小化。在粗轧机中轧制之前，将板坯在隧道炉中在1150 ±10°C下加热并均质化。轧制过程的设计是为了在粗轧机架上实现最大可能的变形量，以便在精轧机上轧制之前对奥氏体进行最佳调节。在轧制6和10 mm钢卷时，板坯厚度分别减少了50%和35%。然后，根据卷的厚度，将最终的厚度减薄量分布在精轧机的5-6个机架上。设计所有参数以在奥氏体区域中实现850 ±10°C的精乳温度并且非常接近Ar 3。轧制后，将钢快速冷却至570±10°C，然后卷取。研究了合金的力学性能和组织演变。拉伸性能，特别是伸长率和YS/UTS比达到良好。CVN在横向方向上的冲击能量被发现是非常高的范围从220至330焦耳。此外，发现冲击转变温度（ITT）低于-70 °C。落锤撕裂试验（DWTT）的结果显示出高达-40 ° C的完全延展性行为，证实了冲击试验结果。通过扫描电镜研究了不同温度下冲击试样的断裂机制。
API X60/X70 line pipe steels are characterized by their higher strength and excellent toughness properties, which are achieved through grain refinement by addition of micro-alloying elements and controlled rolling. Thin slab casting of Nb micro-alloyed steel is a great challenge to the steel producer because of possible transverse cracking of slabs. The major casting parameters, which affect transverse cracking, were critically examined and modified for production of defect free slabs. The hot strip mill parameters were also designed for controlled rolling of slabs to achieve the desired mechanical properties. Three heats (one X60 and two X70) of each 175 ton liquid steel were made and processed into 6, 8 and 10 mm hot rolled coils. In the heat of X60, Nb and Ti were used as micro-alloying elements where as vanadium was also added in X70 heats to achieve the desired strength. The YS/UTS ratio was designed to be below 0.9 by controlling the amount of Si and Mn. During slab casting, liquid core reduction (LCR) was used to reduce the slab thickness from 90 to 70 mm and to minimize the center line segregation and porosity. The slabs were heated and homogenized in a tunnel furnace at 1150 ±10°C before rolling in the roughing mill. The rolling procedure was designed to achieve the highest possible amount of deformation at the roughing stand for best conditioning of austenite before rolling in the finishing mill. 50% and 35% reductions in slab thickness were given for rolling of 6 and 10 mm coils respectively. The final thickness reduction was then distributed over 5-6 stands of the finishing mill depending on the coil thickness. All parameters were designed to achieve finish rolling temperature 850 ±10°C in the austenite region and very near to Ar3. After rolling, the steel was fast cooled to 570±10°C before coiling. Mechanical properties and microstructure evolutions were extensively investigated. The tensile properties particularly the elongation and YS/UTS ratio achieved were good. The CVN impact energy in transverse direction was found to be very high ranging from 220 to 330 Joules. Furthermore, the impact transition temperature (ITT) was found to be below -70 °C. The results of the drop weight tear test (DWTT) showed fully ductile behavior up to -40°C confirming the impact test results. SEM study was carried out to assess the fracture mechanism of impact-tested specimens at different temperatures.