Patent ID: 9200354
Filing Date: 2015-12-01
Classification: C21D,C22C

Abstract:
1. A rolled steel bar or a wire rod for hot forging comprising: a composition containing, in mass %, C: 0.1 to 0.25%, Si: 0.01 to 0.10%, Mn: 0.4 to 1.0%, S: 0.003 to 0.05%, Cr: 1.60 to 2.00%, Mo: 0.10% or less (including 0%), Al: 0.025 to 0.05%, and N: 0.010 to 0.025%, contents of Cr and Mo satisfying 1.82≦fn1≦2.10 if a value of fn1 expressed by a following formula (1) is given: where an symbol of each element in the formula (1) represents a content of the element in mass %; a balance being Fe and impurities having a composition containing P: 0.025% or less, Ti: 0.003% or less, and O (oxygen): 0.002% or less; a structure including any one of a ferrite-pearlite structure, a ferrite-pearlite-bainite structure, and a ferrite-bainite structure; and a cross section in which a maximum value/a minimum value of an average ferrite grain diameter is 2.0 or less when measurement by observation is randomly carried out in 15 visual fields with an area per visual field set to be 62500 μm