Research Progress on Microstructure of Welded Joint of High Strength Steel

The effects of heat input, alloying elements, cooling rate and strain rate on microstructure of high strength steel welded joint and the latest research progress in situ observation of microstructure of high strength steel by high temperature confocal microscope were reviewed. The transformation mechanism of microstructure in coarse grain heat affected zone of welded joint of high strength steel was summarized. The results show that the contents of martensite, granular bainite and acicular ferrite in the microstructure of high strength steel welded joint can be controlled to reach the optimal proportion by prolonging cooling time, reducing heat input, controlling the content of alloying elements and increasing strain rate by pretreatment, so as to optimize the mechanical properties of high strength steel welded joint. The dynamic process of phase transformation of high strength steel can be observed by high temperature confocal microscope, and the phase transformation principle of high strength steel can be obtained, which can provide guidance for the formulation of high strength steel welding process.