Development And Application Of Magnetic Controlled Submerged Arc Surfacing Welding Equipment With Alternating Double Pulses

Electromagnetic stirring is a newly developing welding technology and used moreand more widely. In recent years, an external magnetic field is usually introduced tosubmerged arc welding for its electromagnetic stirring function which could controlcrystallization in the molten pool and bring about smaller grain size and bettermechanical properties.In the paper, a traditional excitation source was improved and a group of parametersadaptive to the needs of actual production were provided by the newly upgradedmagnetic field generator. A new magnetic head with cooling and insulation system andwelding flux transport system was designed. As a result, a stable magnetic field withoutinterference was produced and the assembly process of welding torch, welding fluxtransport system and welding head was simplified.A series of experiments of Q235B submerged arc welding controlled by an externalmagnetic field were conducted. An orthogonal optimization experiment was performedto studying the impact of magnetic field parameters on hardness of surfacing layers and afurther studying on influencing rules of magnetic field on microstructure and mechanicalproperties of surfacing layers was made. A group of optimized magnetic field parameterswere achieved on the base of experiments above-mentioned. Specifically, themicrostructure of surfacing layers was refined best and the order of cylindrical crystalwas disturbed in conditions of Ip=290A, Ib=100A and f=20Hz. It was confirmed that, themicrostructure of surfacing layers could be only improved by electromagnetic stirring ofexternal magnetic field with appropriate parameters. If the magnetic field parameterswere not adaptive to the welding, electromagnetic damping would be produced and theheat transfer and liquid flow would be suppressed and the grain size would be increasedunexpectedly. It was shown that, among peak current, basic current and frequency, thepeak current played the leading role in affecting the hardness of surfacing layers and the frequency was the second and the basic current could hardly have an effect. The grainsize decreased from38.10μm without magnetic field to27.16μm with proper magneticfield, and correspondingly the hardness of surfacing layers increased from35.5HRC to39.5HRC.