Research On Microstructure And Property Of 617B Alloy Used For 700℃ USC Boiler

Alloy 617 is solid solution reinforced nickel based alloy with Ni-Cr-Co-Mo matrix.It was modified to form alloy 617 B to meet the requirement of 700℃ USC boiler.The chemical composition of alloy617 B is more constrained than 617,lower Fe upper limit,lower C upper limit,higher Co lower limit,less Al and Ti and a little B contented,to improve creep strength and welding property.In this paper,analysis of chemical composition,room temperature mechanical properties,microstructure,microstructure and properties after aging,properties of creep rupture were carried out to investigate the microstructure,properties and mechanical property under long-term service.The reason of creep rupture was determined by analyze creep sample.In addition,this paper analyzes the application prospect of 617 B in 700 ℃ USC boiler by comparing the mechanical properties,technological properties and economy of 617 B,HR6W and 740 H.The results showed that 617 B in solution state had good plasticity,the elongation of longitudinal was higher than transverse.The precipitates in the tissue increased to form precipitation strengthening after 980℃×3h de-stress heat treatment,as a result,the hardness improved 35 HBW,strength improved 100 MPa,while the shaping decreased from 81% to60%.Good impact toughness at room temperature and-40 ℃ were showed,the results were 150 J both.It showed good mechanical properties and stability after long time aging,the extension of the precipitated phase on the grain boundary had tendency to grow up while there is no such behavior in the grain,and the mechanical properties can remain basically stable,tensile strength were maintained at more than1000 MPa,elongation were maintained at about 35%,hardness were maintained at more than 250 HBW,impact toughness were maintained at more than 55 J.Because the precipitation phase on the grain boundary accumulated and grew,the samples in 700℃ creep test were fractured along the grain boundary,the creep strength was 146 MPa extrapolated to100000 hours.617B used for 700 ℃ USC boiler is suitable for manufacturing header and pipeline with temperature of 660-720 ℃ considering mechanical properties,technological properties and economy.