Design And Development Of High Strength And Toughness Welding Wire For Microalloyed Steel

By adding various alloying elements and adjusting the content of carbon, a new-type ofhigh strength and high toughness gas-shielding welding wire with low carbon content wereprepared. The relationship and impact factor between microstructure and property of weldmetal and the interactions among alloying elements to microstructure were studied. For theexisting problems of copper coating welding wires, the composite plating technology wasadopted in this study. With consideration of actual welding production process and costrequirement, the new-type plating welding wire for gas-shielding welding with the strength ofmore than700MPa was developed.The results are as followed:（1） The microstructure of welding wire prepared in this subjectmainly consists of fine uniform acicular ferrite, and its tensile strength is more than700MPa inwhich the highest is1100MPa, and it has good plasticity, the average of micro-hardness is morethan260HV0.3（2） The welding wire has good performance of welding process and thedeposited metal primarily consists of fine uniform acicular ferrite. The tensile strength can reach700MPa, the impact of the toughness in-20℃is more than76J. From the impact fracture ofenergy spectrum it can be seen the impact fracture of deposited metal uniformly distributesspherical oxide, carbide and nitride which are TiO₂, MnO, TiN, TiC, etc, and these inclusionsstrengthen and toughen the deposited metal greatly.（3） By analyzing the influence of variousparameters on the coating, the best plating processes of Ni-TiO₂composite electroplating wasdetermine: PH of3-5.5, plating temperature of35℃, current density of2.5A/dm²ï¼Œplating time of1h, TiO₂content of24g/L. The coating is uniform and has good combination with base metal.The coating with the thickness of74μm consists of lots of Ni particles and a small amount ofreunion shaping TiO₂wrapped up by Ni. Compared to that of no coating welding wire themicrostructure of the deposited metal is well fine.（4） The Ni-Cu compound coating is smooth,uniform, density, and with no crack. The best plating process is determined by analyzing theinfluence of various parameters on the coating which are nickel plating time of15s, densitycathode of nickel plating of4A/dm²ï¼Œcopper plating time of60s, density cathode of copperplating of20A/dm², bath temperature of55℃, NiSO₄ï¹'6H₂O content of300g/L, NiCl₂6H₂Ocontent of30g/L, H₃BO₃content of30g/L, CuSO₄ï¹'5H₂O content of285g/L, H₂SO₄content of 70g/L.