高强韧耐候桥梁钢Q690qNH的防断选材及验收方法

 针对TMCP+T和QT 2种工艺生产的40 mm厚Q690qNH耐候桥梁钢板,分别采用GB/T 228.1—2010和GB/T 229—2020标准进行了纵向表面、1/4、心部和横向表面的室温拉伸试验和-120～+20 ℃系列温度夏比V型冲击试验;采用GB/T 5482—2007和GB/T 6803—2008标准进行了纵向表面、心部和横向表面的-120～+20 ℃系列温度动态撕裂试验和P2型的无塑性转变温度落锤试验;采用GB/T 21143—2014和Q/725-1182—2005标准进行了纵向的裂纹尖端张开位移(CTOD)试验和全厚度深缺口宽板拉伸试验,并对各试验结果及其相关关系进行了分析,同时采用光学显微镜观察了2种工艺钢板不同厚度处的金相组织以及采用SEM扫描电镜观察了CTOD试样断口形貌,结合BS 7910的失效评定FAD图,以及典型桥梁焊接构件断裂驱动力的估算,对高强韧耐候桥梁钢Q690qNH的防断选材及验收方法进行了讨论。结果表明,QT工艺钢板的横纵向和厚度方向的强度更加均匀,其塑性、冲击、动态撕裂、CTOD以及断裂韧度K_C等性能较好,可作为D级钢用于关键构件的使用,但作为E级钢,即使用于一般构件也存在风险,而TMCP+T工艺钢板断裂韧性较差,即使作为D级钢也是不符合防断选材要求的;对Q690qNH试验钢,采用1/4厚度处纵向冲击试验的脆性快速增加开始温度作为其防断判据及验收具有良好的可靠性和适用性,作为关键构件使用时,1/4厚度处纵向冲击断口纤维断面率应高于97.5%且冲击吸收功不低于125 J。

Material selection and acceptance of fracture resistance for high strength and toughness weather-resistant bridge steel of Q690qNH

For the 40 mm thick Q690qNH weathering steel plates for bridge produced by TMCP+T and QT processes, tensile tests on longitudinal surface, longitudinal 1/4, longitudinal center and transverse surface at room temperature and Charpy V-shaped impact tests at -120 -+20 ℃ were carried out according to GB/T 228.1—2010 and GB/T 229—2020 standards respectively, and series temperature dynamic tearing tests of -120-+20 ℃ and type P2 non-plastic transition temperature drop hammer tests on longitudinal surface, longitudinal central and transverse surface were carried out according to GB/T 5482—2007 and GB/T 6803—2008 standards respectively, and longitudinal crack tip opening displacement (CTOD) tests and full-thickness deep notched wide plate tensile tests were carried out according to GB/T 21143—2014 and Q/725-1182—2005 standards. Then the experimental data and their correlations were analyzed, at the same time, the metallographic structure of different thickness of steel plate of two kinds of process were observed by using optical microscope, and the fracture morphology of experimental CTOD samples were observed by scanning electron microscope (SEM), and combining with the failure assessment FAD diagram of BS 7910 and the estimation of fracture driving force of typical bridge welded members, the material selection and acceptance method of fracture resistance for high strength and toughness weathering bridge steel Q690qNH were discussed. Results show that the steel plate with QT process has more uniform strength in transverse, longitudinal and thickness directions, and its plasticity, impact, dynamic tear, CTOD and fracture toughness K_C are better, and can be used as D-class steel for key components. However, if it is used as E-class steel, even for general components, there is a certain risk. While the steel plate with TMCP+T process has poor fracture toughness, and even as D-class steel, it does not meet the requirements of material selection based on fracture resistance. It also shows that the rapid increase of brittleness starting temperature at 1/4 thickness of longitudinal impact test has good reliability and applicability as the breaking criterion and acceptance of test Q690qNH weather-resistant bridge steel. When used as a key component, the fiber area ratio at 1/4 thickness of longitudinal impact fracture should be higher than 97.5% and the corresponding impact energy should not be less than 125 J.