Patent ID: 11214847

Abstract:
A high-strength hot-rolled steel sheet for an electric resistance welded steel pipe has decreased variations in in-plane material properties, high strength, and excellent ductility. The high-strength hot-rolled steel sheet has a composition containing, in mass %, C: 0.10 to 0.18%, Si: 0.1 to 0.5%, Mn: 0.8 to 2.0%, P: 0.001 to 0.020%, S: 0.005% or less, Al: 0.001 to 0.1%, Cr: 0.4 to 1.0%, Cu: 0.1 to 0.5%, Ni: 0.01 to 0.4%, Nb: 0.01 to 0.07%, N: 0.008% or less, and further Mo: 0.5% or less and/or V: 0.1% or less so that Moeq defined as Moeq=Mo+0.36Cr+0.77Mn+0.07Ni is 1.4 to 2.2, and Mo and V are contained to satisfy 0.05≤Mo+V≤0.5; and has a microstructure containing, in volume fraction, 80% or more of a bainite phase as a primary phase and 4 to 20% of a martensite phase and a retained austenite phase in total as a secondary phase, where the bainite phase has an average grain size of 1 to 10 μm.