620℃高效火电机组用CB2铸钢件材质特性与质量状态分析

Analysis of Materials Characteristics and Quality State of CB2 Steel Castings for 620℃High-efficiency Ultra-supercritical Steam-Turbine Unit

我国自2013年以来大力发展620℃高效超超临界发电技术,随着再热蒸汽温度提升至620℃,机组再热系统面临着更严峻的服役环境,传统12%Cr马氏体耐热钢难以满足汽轮机关键部件的服役要求,因此必须采用性能更优异的CB2铸钢来制作汽轮机高温内缸和主汽阀门等大型铸件。本文系统阐述了大型CB2铸钢件的制造工艺、关键工序、合金化原理及主要性能特点,并对不同厂家CB2铸钢件的质量状态进行了对比分析,掌握了国内外不同厂家CB2铸钢件之间的性能差异。结果表明,国产与进口CB2铸钢件的化学成分、常规力学性能处于同一水平,金相组织均为回火马氏体,但国产CB2铸钢件相对于进口产品在晶粒度、非金属夹杂物、δ-铁素体含量控制等方面还存在一定差异。上述研究结果可为CB2铸钢件的采购、订货、质量验收提供技术依据,并为CB2铸钢件的质量改进提供技术参考。

The development of 620℃high-efficiency USC power generation technology has gained intensive attention from China since 2013.The reheating system of the unit is facing a more severe service environment,as the temperature of reheated steam rises to 620℃.Hence,the traditional 12%martensitic heat-resistant steel cannot meet the service requirements of the key components of steam turbine,and CB2 steel cas-tings with better performance are thought to be good candidate for the manufacturing of massive castings,such as IP inner cylinder,and main or reheat steam valve.Herein,we systematically demonstrated the manufacturing process,key procedures,alloying principles,and main perfor-mance characteristics of CB2 steel castings.Moreover,the quality status of CB2 steel castings manufactured by domestic and imported manufacturers was compared and analyzed.It was found that the chemical composition and mechanical properties of those castings were comparable,with tempered martensite as the metallographic structure.However,compared with the imported products,the domestic CB2 steel castings still possessed some shortcomings in some aspects,involving precise control of grain size,non-metallic inclusions,and delta-ferrite content.It is believed that the conclusions can provide technical reference for the purchase,order,quality assessment of CB2 steel castings,and pave the way for their quality improvement of CB2 steel castings.