Mechanism For Improving The Toughness Of 00Cr13Ni5Mo Multilayer And Multipass MAG Welding Deposited Metals

China is focusing on the development of large-scale forging and welded structure impulse turbine runner,the room temperature impact absorption energy of welded joints is required to be greater than 100 J.At present,the toughness of MAG welding deposited metals is low in the flat welding position of HS13/5L supermartensitic stainless steel wire for hydraulic turbine runner,and the toughness is greater than 100 J in the vertical-up welding position.In this paper,the deposited metals in the two welding positions are compared,and the mechanism of improving the toughness of multilayer and multipass deposited metals of supermartensitic stainless steel is discussed and verified by experiments.Firstly,the impact properties of MAG deposited metal s in the two welding positions is studied.It is found that the fracture mechanism of the deposited metals is microporous aggregation fracture.A large number of spherical oxides may be as the crack source in the process of impact fracture.The impact toughness of the deposited metals welded in the vertical-up welding position is excellent.After tempering treatment at 590°C for 8h,the impact absorbed energy at room temperature can reach more than 100 J.Then,the chemical composition and microstructure of the deposited metals in the two welding positions are systematically compared.It is found that the different welding position does not affect the chemical composition and phase composition of the deposited metals.The reversed austenite microstructure formed by tempering can significantly improve the toughness of the deposited metals of supermartensitic stainless steel,and the content of reversed austenite is about 13%.It is found that the number of inclusions in the deposited metals is different between the two welding positions.The number of oxide inclusions in the deposited metals is less in the vertical-up welding position,which is one of the reasons for the high toughness of the deposited metal s in the vertical-up welding position.It is found that the different distribution of the weld bead in the two welding positions cause more recrystallization zones at the notch position of the impact specimen of the vertical-up welding deposited metals,which increases the resistance to crack formation and propagation,and thus improves the impact toughness of the deposited metals,which is the main reason for the high toughness of the deposited metals in the vertical-upward welding position.Finally,the mechanism is verified by experiments.The increase in the number of welds in the crack propagation zone of the deposited metal s impact specimen can correspondingly increase the proportion of recrystallization zone,which can significantly improve the crack propagation energy of the deposited metals.The MAG swing welding process can form more welding pass at the center of the weld,and the MAG welding deposited metals of supermartensitic stainless steel can also be obtained in the flat welding position with room temperature impact absorption energy greater than100 J.In this paper,the mechanism of improving the toughness of deposited metals by multilayer and multipass MAG welding of supermartensitic stainless steel is expounded,and the process improvement measures to improve the impact toughness of the deposited metals by increasing welding passes is put forward,which provides reference for the welding manufacturing of large impulse turbine runner.