Design Of Welding Wires And Study Of Welding Process On Low Alloy High Strength Steel

The strength and toughness of low alloy high strength steel are further improved as the development of metallurgy technology and the adoption of new processes such as TMCP and microalloying nowadays. The demand of obdurability, safety and stability of the welding joint is also becoming higher. The 800 MPa low alloyed high strength steel has been used in some fields such as sluice gate and penstock of hydropower station, hull structure, bridge and tall buildings. Two kinds of new welding wires are designed and the microstructures and properties of the deposits are analysed. The microstructures and properties of deposits welded under different shielded gases were investigated. The nonmetallic inclusions in the deposits are also observed.The experiment results indicated that the microstructures were mainly lath-shaped low carbon martensite when welding with pure argon gas. The deposits had very high strength and the tensile strength exceeded 900MPa. The plasticity and toughness decreased slightly. The microstructures of deposits were mainly acicular ferrite when welding with Ar+（5²0）%CO₂ mixed gas. The deposits had good strength and excellent toughness. The deposit welded with low nickel welding wire had higher impact toughness under -20℃and the deposit welded with high nickel welding wire had better toughness under -50℃.There are some spherical nonmetallic inclusions in the weld metals when welding under shielded gas and they mainly are the oxides of silicon, manganese, titanium and aluminium. The diameters of these nonmetallic inclusions are usually 0.2⁰.6μm. There is only a few nonmetallic inclusions in the deposits when welding with pure argon. No acicular ferrite generated duo to the high hardenability of the weld metal. The number of the nonmetallic inclusions became very large when welding with Ar+（5²0）%CO₂ mixed gas and with the decrease of hardenability, a great number of acicular ferrite emerged in the weld metal and the plasticity and toughness are better.