Structural low alloy thick steel for friction stir welding and structural friction stir welding joints

摘要

PROBLEM TO BE SOLVED: To provide a structural use low alloy thick steel material that is excellent in workability during friction stir welding and is excellent in strength and toughness of friction stir welded part.SOLUTION: By having a composition such that a ferrite phase of 20% or more in volume fraction is formed in an equilibrium state at 900°C and furthermore it is a structure in which 10 or more precipitates are precipitated per 100 μm, containing C: 0.05 to 0.20%, Si: 0.1 to 1.0%, Mn: 0.1 to 3.0%, N: 0.001 to 0.010%, Al: 0.02 to 1.0% and containing such that Si and Al satisfy (Si+2.5Al)≥1.5, and furthermore it has a composition containing one or two selected from the group consisting of V: 0.1 to 1.0% and Nb: 0.1 to 1.0%, a structural use low alloy thick steel material in which the deformation resistance during friction stir welding is lowered, the workability during friction stir welding is improved as well as the coarsening of the structure of the welded part is suppressed, and a friction stir welded part having excellent strength and toughness can be obtained is produced.SELECTED DRAWING: None