Structural steel materials with excellent fatigue crack propagation characteristics and coating durability and their manufacturing methods

摘要

PROBLEM TO BE SOLVED: To provide a structural steel material having excellent fatigue crack propagation characteristics and coating durability. SOLUTION: In mass%, C: 0.020% or more, 0.200% or less, Si: 0.05% or more, 1.00% or less, Mn: 0.20% or more, 2.00% or less, P: 0.003% or more, 0.030% or less, S: 0.0001% or more, 0.0100% or less, Al: 0.001% or more, 0.100% or less and W: 0.005% or more, The composition is composed of 1,000% or less, the microstructure of the steel material is a composite structure composed of a hard phase and a soft phase, the body integration ratio of the hard phase is 0.20 to 0.80, and the soft phase. The average particle size of ferrite, which is the main phase of the above, is 5 to 50 μm. [Selection diagram] None