Effect Of Ni,Zr And Mo On The Microstructure And Mechanical Properties Of Deposited Metal Of Self-shielded Flux Cored Wire Under Great Heat Input

Currently,the welding of X80 pipeline steel using self-shielded flux cored wire is limited in practical promotion and application owing to adopting low welding voltage and current at home and abroad,which always leads to a low welding heat input and its low welding efficiency.Therefore,with the condition of the great heat input during the welding,the effect of alloy elements in the flux on microstructure and properties of the deposited metal is worthy discussing.And it can provide theoretical basis and data reference for the research and development of self-shielded flux cored wire used for the great heat input welding.In this paper,the welding experiments were carried out with the great heat input(U: 28 V,I: 350 ~ 370 A,V: 230 mm / min).The effect of Ni,Zr,Mo in the core powder on the microstructures and properties of deposited metals obtained from the self-shielded flux cored wire used for great heat input welding was investigated by OM,SEM,XRD,impact and tensile tests.The results showed that Ni had little effect on the spatter rate of welding and the slagging of welds.When the content of Ni was 6wt.%,lots of acicular ferrite in deposited metal were produced resulting in the high strength and the best low temperature toughness of the deposited metal.When the Ni content was 9wt.%,the content of acicular ferrite decreased while the content of ferrite is increased in the deposited metal.And the strength of deposited metal was the highest,but the low temperature toughness decreased.With the increase of Zr,the rate of spatter decreased first and then increased while the rate of slagging increased first and then decreased.When the Zr content was1 wt.%,the acicular ferrite got the largest amount,and the low-temperature impact energy of the deposited metal was the highest.When the Zr content was 2wt.%,the amount of acicular ferrite in the deposited metal decreased while the amount of the pro-eutectoid ferrite increased.And the toughness of the deposited metal decreased while the intensity was the highest.Mo had little effect on the rate of spatter and the slagging of welds.When the content of Mo was 2wt.%,the largest amount of carbide was precipitated in the deposited metal,which indicated the most obvious precipitation strengthening occured to the deposited metal resulting in the highest strength and poor low temperature toughness.When the Mo content reached 3wt.%,the fine acicular ferrite in deposited metal had the largest number while the precipitates were less.And at that time,the low temperature toughness of the deposited metal was the highest while the strength decreased.