HIGH-CARBON HOT-ROLLED STEEL SHEET AND PROCESS FOR PRODUCING THE SAME

摘要

A process for producing a high-carbon hot-rolled steel sheet which is a hot-rolled spheroidized annealed material, which comprises a step in which a steel containing 0.2-0.7 mass% carbon is hot-rolled at a finish temperature not lower than [(transformation point A_r3)-20°C] to form a hot-rolled sheet, a step in which the hot-rolled sheet is cooled to a temperature of 650°C or lower at a cooling rate of 60-120 °C/sec, excluding 120°C/sec, a step in which the hot-rolled sheet after cooling is wound up at a winding temperature of 600°C or lower, and a step in which the hot-rolled sheet after winding is annealed at an annealing temperature of from 640°C to the transformation point A_c1. The high-carbon hot-rolled steel sheet thus obtained is excellent in both of stretch flangeability and evenness of hardness in the sheet-thickness direction.