| 摘要 |
PROBLEM TO BE SOLVED: To obtain a non-refined steel material for a weld bolt in which the total heat treatments in a bolt production process till annealing, quenching, tempering and bluing can be obviated, having excellent weldability, and in which the generation of rust in a weld zone is suppressed without damaging its workability.SOLUTION: Provided is a non-refined steel material for a weld bolt having a prescribed componential composition, having a microstructure in which the area faction of bainite is 80% or higher, and also, the area fraction of the bainite crystal grains directly adjacent to two or more ferrite crystal grains is 30% or higher, and having a tensile strength of 650 to 800 MPa. |
