Microstructure and properties of 9Cr-3W-3Co steel joint by shielded metal arc welding

In the view of the application of 9Cr-3W-3Co new martensitic heat-resistant steel as the material of ultra-supercritical thermal power, the welding material (deposited metal) for the shielded metal arc welding is designed and multi-layer and multi-pass welding is carried out. The microstructure of the 9Cr-3W-3Co joint was analyzed by optical microscopy and scanning electron microscopy. The hardness, tensile strength, and impact absorption energy of the joints were investigated. The results show that the microstructure of the upper and middle parts of the welded metal is tempered martensite, carbide particles, and M-A components, and the lower part of the welded metal is composed of tempered martensite, acicular δ ferrite, and carbide particles. The micro-hardness distribution of the different parts of the joint is basically the same. From the welded metal through the HAZ to the base metal, its hardness gradually decreases, and the average hardness of the joint is 288 HV. The average tensile strength of the joint is 631 MPa, which is 0.84 of the base metal. The fracture position is in the welded metal area, and the fracture behavior is brittle fracture. The average impact absorption energy of the 9Cr-3W-3Co steel joint is 17 J, which is lower than that of the base metal.