Effect of Heat Input on the Metal Microstructure and Mechanical Properties of Q960 High‐Strength Steel Solid Core Welding Wire

The self‐developed Q960 high‐strength steel solid wire with different heat input is welded by MIG welding to solve the problem of insufficient low‐temperature toughness of Q960 steel weld. The effect of heat input on the microstructure and mechanical properties of butt welding deposited metal is studied in depth. The results show that the microstructure of deposited metal is composed of granular bainite (GB), degenerate upper bainite (DUB), martensite (M), and acicular ferrite (AF). DUB and M play key roles as strengthening phases, whereas GB and AF serve as primary toughening phases. Elevated heat input leads to a progressively rougher microstructure in the deposited metal. AF and DUB increase first and then decrease, GB increases and M decreases slightly. The inclusions conducive to AF nucleation are mainly composed of oxides of Mn, Si, Ti, and Mn sulfide with sizes between 100 and 500 nm. At a 14 kJ cm −1 heat input, the complex phase microstructure effectively refines the grain, and the high‐angle grain boundaries and ferrite interlocking structure optimize the strength and toughness balance of the deposited metals. The tensile strength measures 958 MPa, with the highest elongation at 19% and an average impact toughness of 50 J at −40 °C.