Steel wire for non-heat treated machine part, and non-heat treated machine part

Provided is a steel wire for a non-heat treated machine part, said steel wire containing, by mass%, 0.40-0.65% C, 0.05-0.50% Si, 0.20-1.00% Mn, and 0.005-0.050% Al, with the remainder comprising Fe and impurities, wherein the metallographic structure contains at least (35*[C%]+65)% pearlite, and, if the diameter is taken as D, the average aspect ratio of the pearlite block at a depth of 50 [mu]m in an L cross-section is taken as AR, and the average block grain diameter of the pearlite block at a depth of 50 [mu]m in a C cross-section is taken as GD, the following conditions are satisfied: AR is at least 1.4; (AR)/(the average aspect ratio of the pearlite block at a depth of 0.25D in the L cross-section) is at least 1.1; GD does not exceed (15/AR) [mu]m; and (GD)/(the average block grain diameter of the pearlite block at a depth of 0.25D in the C cross-section) is less than 1.0.