| 摘要 |
A steel bar for a steering rack which comprises, in mass %, 0.50 to 0.60 % of C, 0.05 to 0.5 % of Si, 0.2 to 1. 5 % of Mn, 0.0005 to 0.003 % of B, 0.005 to 0.05 % of Ti, 0.0005 to 0.1 % of Al and 0.002 to 0.02 % of N, wherein quenched and tempered structures of the portion located at a depth from the surface of the steel bar of D/4, wherein D is the diameter of the steel bar, satisfy the following requirements I), II) and III): I) the area percentage of the sum of tempered bainite and tempered martensite structures is 30 to 100 %, II) the area percentage of a regenerated pearlite structure is 0 to 50 %, and III) the area percentage of the sum of tempered bainite, tempered martensite and regenerated pearlite structures is 50 to 100 %. |
