Research On The Welding Properties Of Q420FRE Steel

Building structures which undergo different load and stress distribution, thus hasdifferent structure forms. In the process of manufacturing and installation, thewelding method and process therefore exhibit diversity. The performance ofheat-affected zone is an important factor influencing the structural integrity and safety.This work aims at investigating transformation and microstructure evolution of theheat-affected zone of the newly developed Q420FRE steel utilizing the Gleeble3800thermal simulator. Different welding methods have also used to analyze themicrostructure and mechanical properties of the weld joint of the investigated steel.Thermal simulation experiment results show that under different weldingthermal cycle conditions, the dominant microstructure of heat-affected zone aregranular bainite. The hardness does not change greatly. The average hardness value isHV0.2185~207. The hardness stability of heat-affected zone implys that theinvestigated steel has good weldability and is suitable for high heat input welding.Results of weld joint mechancial properties under different methods show thatthe Q420FRE steel has excellent weldability. In a wide range of heat inputs,automatic submerged arc welding and gas shielded welding can be applied withmatching welding material. The welding joint has excellant mechanical properties atlow temperature of－40℃. The yield strengths at high temperature and roomtemperature both meet standard requirementss. After one or two times fire, a largenumber of nanosized (Ti, Nb)(C, N) or Nb (Ti), C carbonitrides are formed in theheat-affected zone, which ensures the high temperature strengthening. The yieldstrength at high temperature still reaches the standard requirements even for120minutes fire. Therefore, the welding joint of the Q420FRE steel has an execllant fireresistant performance.