Research Of Organization And Performance Of High Strength Steel Weld Under Magnetic Field

Steel material with high strength, high toughness is the most ideal materials of weldingstructure. To improve the steel strength grade, the mass fraction of carbon and other alloyelements will increase, which will cause the welding joint embrittlement, softening, crackstend to expand and other defects. The emergence of these welding problems largely restrictedthe application of high strength steel.This paper main research content: The longitudina magnetic field was introduced in thewelding of high strength steel Q960. The influence of magnetic field on microstructure andmechanical properties of welded joints was studied by tensile test, impact test, hardness test. Inaddition, optical microscopy and scanning electron microscopy were used to examine themicrostructure, fracture morphology of welding joints, and try to reveal the mechanism of theeffect of electromagnetic stirring on grain refinement and improving mechanical properties ofwelding joints.Best magnetic field parameters was: the field frequency f=20Hz, the field current Ie=2.5A. At this parameters, thrmechanical properties of welded joints was: the tensile strengtharrived839MPa, compared to welded joints under no magnetic field enhanced17.01%; andthe impact energy arrived72J, the joint impact energy compared to joint under thenon-magnetic field increased24.14%. Optimization of the magnetic field for the weld jointmainly through electromagnetic stirring, breaking grains, affecting the number and size ofinclusions and the effect of heat implementation. If the magnetic field parameters over theoptimum value will lead to the hysteresis effect and weaken the effect of electromagneticstirring, etc., which will roughen the tissue and reduce the number of acicular ferrite. Thenumber of inclusions in the magnetic field was reduced and the size becomed smaller, but thenumber of inclusions for acicular ferrite core didn’t diminish. Inclusions in weld joint mainlyincluded Mn, Si, Al, Ti, O and other elements, and Ti-based oxides played an important role inthe process of the acicular ferrite forming.