高强度管线钢落锤撕裂性能的试验

摘要：以X80管线钢为试验材料,采用金相显微镜和扫描电子显微镜,研究了显微组织、M/A、夹杂物对管线钢落锤撕裂性能的影响。结果表明,管线钢落锤撕裂性能（DWTT）随着多边形铁素体体积分数的增加而改善,当多边形铁素体的体积分数超过某一临界值(约28%)后,DWTT性能开始降低;组织中的M/A岛细小且弥散分布,其尺寸控制在纳米级别有利于改善DWTT性能;针对本研究试验钢,若其厚度方向上组织均匀、组织中铁素体体积分数为28%、M/A岛平均尺寸和比例分别为0.42μm和2.8%时,试验钢具有最好的落锤撕裂性能（韧性剪切面积率94.5%）。     

厚规格X70管线钢落锤撕裂试验性能分析

通过金相显微镜、扫描电镜、电子背散射衍射技术对不同工业生产轧制工艺下,不同厚度规格、不同轧制压缩比的X70管线钢的显微组织进行分析,对比其原始奥氏体组织差异,研究了压缩比对原始奥氏体组织的影响。结果表明:轧制过程中大压缩比更有利于细化奥氏体晶粒,提高厚规格X70管线钢低温韧性。但由于精轧过程温度较低无法将变形渗透至中心,因此需进一步借助粗轧过程中的低温阶段进行变形渗透。轧后超快冷冷却可以提高该钢种落锤撕裂试验(DWTT)性能,但不足以弥补前期奥氏体晶粒细化不足而带来的DWTT性能波动。     

板坯加热工艺对厚规格管线钢组织性能的影响

为了改善厚规格管线钢的强韧性,采用实验室物理模拟及轧制试验和SEM、EBSD分析方法,研究了试验钢的奥氏体粗化特性及板坯再加热工艺对30 mm规格管线钢组织性能的影响规律,并分析了强韧化机理。结果表明,随着试验板坯加热温度的上升,试验钢初始奥氏体晶粒呈粗化趋势,试验钢的显微组织由细化的铁素体为主的组织向贝氏体为主的组织转变,钢板强度呈上升趋势,夏比冲击功、DWTT(drop weigh tear test,落锤撕裂试验)性能呈下降趋势;低温加热时,随着保温时间增加,细化贝氏体比例上升,夏比冲击功呈上升趋势,强度、DWTT性能变化不大;高温加热时,随着保温时间增加,夏比冲击功呈下降趋势,强度、DWTT性能变化不大。EBSD分析表明,晶粒粗化显著降低夏比冲击韧性,增加大角度晶界比例有利于提升DWTT性能。     

轧后加热温度对高Nb X80管线钢板组织性能的影响

 采用TMCP（热机械控制处理）工艺制造的高Nb成分X80管线钢板,在实验室进行了不同加热温度下的离线热处理试验研究,分析了轧后加热温度对高Nb管线钢组织性能的影响规律。结果表明：钢板在150~600℃温度范围内热处理时,钢板的显微组织、强度及DWTT（Drop Weight Tear Test,落锤撕裂试验）性能无显著变化,韧脆转变温度略有上升;650℃加热处理后,钢板的显微组织粗化、韧脆转变温度上升,DWTT性能明显下降。     

试样减薄对大壁厚X80级管线钢落锤性能的影响

采用金相显微镜和扫描电镜对30.8 mm大壁厚X80管线钢不同减薄方式下DWTT试样截面微观组织和试验断口进行了分析,目的是研究减薄方式对大壁厚管线钢DWTT性能的影响。结果表明,随着试验温度的降低,单边减薄的DWTT性能优于双边减薄,而且双边减薄试样从表面至心部,贝氏体体积分数逐渐降低,多边形铁素体体积分数逐渐升高,晶粒尺寸变大,MA岛由细小的颗粒状变为尺寸较大的链状,且心部伴随着严重的偏析和夹杂。而单边减薄试样从表面至心部组织整体变化不大;裂纹优先沿着消耗能量最低的部位开裂,所以双边减薄试样心部出现比单边减薄试样严重的解理和逆解理断裂。     

大厚度X70级管线钢的开发

介绍了舞钢大厚度X70级管线钢板的研制过程,分析了大厚度X70级管线钢的化学成分、金相组织及钢板拉伸、系列温度冲击韧性、DWTT等。结果表明：舞钢采用低C高Mn,Nb、Ti微合金,加入适量Mo,控轧控冷工艺生产的28．6mm厚X70钢板强韧匹配性高,综合性能优良,其性能完全符合AP15L对X70级管线钢的要求,成功应用于中亚输送管线“锡尔河穿越工程”。     

试样减薄对大壁厚X80级管线钢落锤性能的影响

摘要：采用金相显微镜和扫描电镜对30.8mm大壁厚X80管线钢不同减薄方式下DWTT试样截面微观组织和试验断口进行了分析，目的是研究减薄方式对大壁厚管线钢DWTT性能的影响。结果表明，随着试验温度的降低，单边减薄的DWTT性能优于双边减薄，而且双边减薄试样从表面至心部，贝氏体体积分数逐渐降低，多边形铁素体体积分数逐渐升高，晶粒尺寸变大，MA岛由细小的颗粒状变为尺寸较大的链状，且心部伴随着严重的偏析和夹杂。而单边减薄试样从表面至心部组织整体变化不大；裂纹优先沿着消耗能量最低的部位开裂，所以双边减薄试样心部出现比单边减薄试样严重的解理和逆解理断裂。     

管线钢落锤撕裂试验方法的建立、应用及发展

回顾和分析了管线钢DWTT方法的建立过程、应用情况以及在高强度、高韧性、大壁厚管线钢中存在的DWTT异常断口问题.在综述目前该问题研究现状的基础上,通过研究和分析,提出了对DWTT异常断口的基本看法和处理方法.     

基于材料组织量化的DWTT性能优化探究

以一种新型管线钢试制过程中DWTT性能改进为例,基于PIDAS提供的工艺—性能数据,通过机器学习与图像识别方法对材料组织进行信息量化分析.结合不同工艺量化信息对比改进工艺参数,通过有限次数试制获得的工艺—组织—性能数据,结合专家经验找出三者之间关联性,进行工艺分析优化设计,快速确定达成良好DWTT性能的工艺设计.     

2250热连轧生产高级别管线钢的工艺控制与组织性能

本文以X80管线钢为例,对2250热连轧生产高级别管线钢的成分设计及工艺控制进行了阐述。对生产的X80级高级别管线钢的力学性能、显微组织、析出物进行了分析研究。结果表明：2250热连轧生产的厚度规格为18.4mm的X80高级别管线钢力学性能优良,平均屈服强度为655MPa,平均抗拉强度为750MPa,屈强比为0.87,-20℃条件下平均冲击功为300J,-15℃条件下DWTT平均纤维断面率为95％。通过对显微组织进行观察发现X80级高级别管线钢的显微组织主要为粒状贝氏体加针状铁素体组织,析出物分布均匀,尺寸约在20nm左右。     

X70管线钢微观组织结构对落锤性能的影响

结合12～33mm厚X70管线钢落锤试验结果,利用光学显微镜和扫描电镜研究和分析不同厚度落锤试样的组织演变规律及组织对落锤性能的影响。结果表明：随着钢板厚度的增加,钢的组织由彼此交织在一起的针状铁素体、多边形铁素体/准多边形铁素体演变成粒状贝氏体＋少量针状铁素体/多边形铁素体,碳化物的析出数量和析出尺寸随之增加。具有交织在一起的非等轴状AF＋PF/QF混合组织的试样落锤性能优于以晶粒粗大粒状贝氏体为基体组织的试样的落锤性能。通过控制M/A岛形态和分布可以提高钢的落锤性能。     

管线钢落锤性能的影响因素分析

本文研究了影响管线钢落锤性能的几个因素,分析了铸坯偏析度。夹杂物、碳化物析出组织均匀性和组织类型对落锤性能的影响．     

Effects of Specimen Thickness and Notch Shape on Fracture Modes in the Drop Weight Tear Test of API X70 and X80 Linepipe Steels

This study is concerned with effects of specimen thickness and notch shape on drop weight tear test (DWTT) properties and fracture modes of API X70 and API X80 low-carbon microalloyed linepipe steels. Detailed fractographic analysis of broken DWTT specimens showed that the fracture initiated in an initial cleavage mode near the specimen notch and that some delaminations occurred at the center of the fracture surface. The chevron notch (CN) DWTT specimens had broader initial cleavage areas than the pressed notch (PN) DWTT specimens. The larger inverse fracture areas (i.e., cleavage areas close the hammer impact side) appeared in the PN DWTT specimens, because their higher fracture initiation energy at the notch allowed a higher strain hardening in the hammer-impacted region. The number and length of delaminations were larger in the CN DWTT specimens than in the PN DWTT specimens, and increased with increasing specimen thickness due to the plane strain condition effect. As the test temperature decreased, the tendency of delaminations increased, but delaminations were not found when the cleavage fracture prevailed at very low temperatures. The DWTT test results such as upper shelf energy (USE) and energy transition temperature (ETT) were discussed with relation to microstructures and fracture modes including initial cleavage fracture, ductile fracture, inverse fracture, and delaminations.     

X80管线钢落锤撕裂性能的影响因素分析

 研究了不同类型的显微组织的落锤撕裂性能,并从夹杂物百分比以及分布角度分析了夹杂物对落锤性能的影响,并给出了典型硅酸盐类夹杂和硫化物、氧化物夹杂的扫描照片,利用lapera试剂腐蚀出M/A岛的形貌,分析了M/A岛对落锤性能的影响,以及析出物位错、析出物的强化机制。     

Microstructure Refinement and Precipitation Characteristics of TMCP-Processed Plates for Pipeline Applications

The influence of technological parameters of controlled rolling and accelerated cooling (TMCP-processing) on microstructure and mechanical properties of plates with thickness of 25 mm and more at the mill "5000" of OJSC "Мagnitogorsk Iron and Steel Works" were investigated.The necessity of formation of fine-grained ferrite-bainite microstructure without elongated areas of coarse lath bainite for achievement of DWTT properties is proved.Precipitation conditions and type of Nb(C,N) and (Nb,V)(C,N) particles with the size of less than 10 nm in the process of rolling and additional tempering are defined.     

Effects of microstructure on inverse fracture occurring during drop-weight tear testing of high-toughness X70 pipeline steels

The effects of microstructure on inverse fracture occurring in the hammer-impacted region were analyzed after conducting a drop-weight tear test (DWTT) on high-toughness pipeline steels. Three kinds of steels were fabricated by varying the alloying elements, and their microstructures were varied by the rolling conditions. The pressed-notch (PN) or chevron-notch (CN) DWTT and Charpy V-notch (CVN) impact tests were conducted on the rolled steel specimens, and the results were discussed in comparison with the data obtained from CVN tests of prestrained specimens. In the hammer-impacted region of the DWTT specimens, abnormal inverse fracture having a cleavage fracture mode appeared, and the inverse fracture area correlated well with the upper-shelf energy (USE) obtained from the CVN test and with the grain size. The steel specimens having a higher USE or having coarse polygonal ferrite tended to have a larger inverse fracture area than those having a lower USE or having fine acicular ferrite. This was because steels having a higher impact absorption energy required higher energy for fracture initiation and propagation during the DWTT. These results were confirmed by the CVN data of prestrained steel specimens.