摘要
超超临界火力发电技术是一种清洁高效的发电技术,它可使机组在更高的工作温度和蒸汽压力下运行,从而有效地提高机组热效率,减少燃料的消耗和有害气体的排放,故近年来得到了迅猛发展。P92钢以其优异的抗蠕变、抗氧化和耐腐蚀性能,较高的高温强度和导热率,良好的焊接性能,以及较低的热膨胀系数被广泛用作超超临界发电机组主蒸汽管道和再热蒸汽管道。但由于该钢合金含量高,焊接时熔池黏度较大,流动性相对较差,故其焊接接头易出现裂纹等缺陷,严重威胁着超超临界机组的安全运行。为了保障超超临界机组的安全运行,采用光学显微镜、扫描电镜和透射电镜对1 000 MW超超临界发电机组P92钢再热蒸汽管道焊接接头中出现的缺陷以及显微组织对缺陷形成的影响进行深入的研究,结果表明:焊接接头中有大量圆形或椭圆形的白色斑点,其中一些斑点内有呈放射状分布的发丝状裂纹,且白色斑点处富钼,白色斑点多的区域氢的质量分数明显高于无白色斑点区域,表明这些缺陷为氢致裂纹(即白点)。与无白点区域相比,白点多区域马氏体板条更细密,板条形态保持得更好,析出相尺寸更小,表明白点更易在马氏体回复程度低的区域产生。
In order to make better use of fossil fuels and reduce emissions of CO2, there is a demand for increasing the thermal efficiency of fossil-fired power plants by raising operating temperatures and pressure. Therefore, the ultra super-critical（USC） power plants with improved thermal efficiency have been built in the past decades. P92 steel has been recognized as excellent ferritic heat-resistant steel for USC boilers because it exhibits high creep rupture strength, excellent thermal conductivity, low coefficient of thermal expansion, and good processing ability accompanied with satisfactory resistance to stress corrosion cracking and oxidation. However, defects（cracks, for example） are easy to form in P92 steel welded joint due to relatively large viscosity and poor liquidity of molten pool caused by high content of alloy elements, which would seriously affect the safe operation of the USC unit. In this paper, the defects in welded joint of a hot reheat steam pipe of a USC unit after long-term service are studied to ensure the safe operation of the USC unit. The results show that there exist a large number of circular or elliptic white spots in welding joint and hairline cracks initiate in some of the white spots. The molybdenum levels are greatly higher in the white spots than in other zones and the hydrogen content of the zone with the white spots is also higher than that of white-spot free zone, implying that the defects in welded joint are hydrogen-induced cracks, namely white flakes. The microstructure observation on the zones with and without the white flakes reveals that the martensite lath width is smaller, the morphology of lath martensite remains better and the size of the precipitates is smaller in the former than in the latter, suggesting that the recovery extent of the zone with white flakes is lower than that of white-flake free zone.
出处
《机械工程学报》
EI
CAS
CSCD
北大核心
2017年第18期113-120,共8页
Journal of Mechanical Engineering
