ROLLED STEEL BAR OR WIRE FOR HOT FORGING

摘要

Disclosed is a rolled steel bar or wire for hot forging, which has a chemical composition that contains 0.10-0.20% of C, 0.01-0.30% of Si, 1.00-2.30% of Mn, 0.040% or less of S, 0.10-0.80% of Cr, 0.010-0.080% of Al, 0.0002-0.0050% of B, 0.010-0.080% of Ti and 0.0020-0.0080% of N, with the balance made up of Fe and impurities, while limiting P to 0.040% or less, Cu to less than 0.10%, Ni to less than 0.10%, Mo to less than 0.05% and V to 0.01% or less among the impurities, in said chemical composition [Ti - 3.4N = 0.001] being satisfied, Ceq represented by a specific formula of C, Si, Mn, Ni, Cr, Mo and V being 0.57 or less, and DI represented by a specific formula of C, Si, Mn, P, S, Cr, Ni, Mo and Cu being 70-170. The rolled steel bar or wire for hot forging has 10 or more Ti precipitates having a circle-equivalent diameter of 0.07-1.0 µm and 10 or more Ti precipitates having a circle-equivalent diameter of 0.01-0.05 µm in an area of 100 µm2. Since the rolled steel bar or wire for hot forging is weldable and has excellent strength and toughness of the matrix and excellent toughness of HAZ, the rolled steel bar or wire for hot forging is suitable as a material for underbody components of automobiles such as a spindle.