Patent ID: 11035021

Abstract:
A high-strength steel sheet includes: a specific chemical composition; and a microstructure represented by, in a ⅛ thickness to ⅜ thickness range with ¼ thickness of a sheet thickness from a surface being a center, in volume fraction, ferrite: 85% or less, bainite: 3% or more and 95% or less, tempered martensite: 1% or more and 80% or less, retained austenite: 1% or more and 25% or less, pearlite and coarse cementite: 5% or less in total, and fresh martensite: 5% or less, in which the solid-solution carbon content in the retained austenite is 0.70 to 1.30 mass %, and to all grain boundaries of retained austenite grains having an aspect ratio of 2.50 or less and a circle-equivalent diameter of 0.80 μm or more, the proportion of interfaces with the tempered martensite or the fresh martensite is 75% or less.