Cold Cracking Sensitivity of a Newly Developed 9Cr2WVTa Steel

Cold cracking susceptibility of the newly developed 9Cr2WVTa steel plate welded with the corresponding gas tungsten arc welding wire has been evaluated using the implant test and the Y-groove cracking test. Measurement of diffusible hydrogen content shows that the welding wire is ultra-low welding consumables (0.40 mL/100 g). Results of the implant test show that the fracture critical stress without pre-heating is only 300 MPa and increases up to the yield strength with pre-heating to 150 °C. The fracture critical stress under high heat input decreases to 250 MPa owing to the formation of quenched microstructure. Fractographies show ductile dimple fracture under higher loads and quasi-cleavage fracture under lower loads. Results of Y-groove cracking tests show that the minimum pre-heating temperature is 150 °C and the maximum transverse residual stress is located at the root of the weld metal. Therefore, the heat input should be chosen in a proper range and the pre-heating temperature is no less than 150 °C.