Heat non-heat treated steel for hot forging and high toughness

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PROBLEM TO BE SOLVED : To provide a non-refining steel which has high toughness on a level which can not always stably attained by the conventional non-refining steel even if heat treatment after hot forging is obviated in a process of producing machine parts. SOLUTION : The high toughness non-refining steel has a composition containing, by mass, 0.1 to 0.6% C, 0.01 to 2.0% Si, 0.2 to 2.0% Mn, 0.005 to 0.5% S, 0.1 to 2.0% Cr, 0.005 to 0.1% Ti, 0.003 to 0.02% N, 0.0 to 0.07% Al, 0.001 to 0.1% Sn, and further containing 0.005 to 0.1% Rem (one or more kinds selected from rare earth metals such as Ce, La and Nd) and 0.0005 to 0.005% Ca, and also satisfying the relation of (Rem%+Ca%)/(S%)>=0.05, and the balance Fe with inevitable impurities. The average diameter of the equivalent circle of inclusions is <=20 &mu m, and the average aspect ratio (length/width) of the inclusions is <=10.