Study on Microstructure and Precipitates of 9Cr-2W Heat-resistant Steels

Microstructure and precipitates of 9Cr-2W heat-resistant steels were studied using optical microscopy,scanning electron microscopy and transmission electron microscopy.Results show that the microstructure of normalized 9Cr-2W steel is martensite,consisting NbX precipitates of size 10-100 nm and needlelike cementite of a few tens of nm;the microstructure of tempered 9Cr-2W steel is tempered martensite,including M_(23)C_6 precipitates of 100-300 nm and MX precipitates of about 50 nm;the fracture microstructure of 9Cr-2W specimen after creep-rupture test at 650 ℃/110 MPa is still tempered martensite,and apart from M_(23)C_6 and MX precipitates,Laves phase of 100-500 nm can also be found,mainly on its lath boundary.