PURPOSE:To ensure strength and toughness equal to or higher than those of the conventional tempered material in an as-hot-forged state, e.g., by specifying respective contents of oxide-forming elements, such as Ti and Zr, in a medium carbon steel and incorporating the grains of oxide and composite body of oxide and MnS having a specific grain size. CONSTITUTION:A medium carbon tough and hard steel has a composition consisting of, by weight ratio, 0.10-0.60% C, 0.01-3.00% Si, 0.20-3.00% Mn, 0.01-0.30% S, 0.03.0.30% V, 0.005-0.060% N, further one or more kinds among 0.001-0.100% Ti, 0.001-0.100% Zr, 0.001-0.200% Hf, 0.001-0.150% Y, 0.001-0.150% La, 0.001-0.150% Ce, 0.001-0.050% Ca, and 0.001-0.010% Mg, and the balance Fe with inevitable impurities. Further, the grains of oxide and composite body of oxide and MnS of 0.1-l0mum grain size are incorporated by 1X103 to 1X106 pieces/mm3. Moreover, the contents of Al and P are limited to =0.005% and =0.03%, respectively. By this method, a steel having superior strength and toughness in an as-hot-forged state can be obtained while obviating the necessity of tempering treatment.
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机译：目的：确保在热锻状态下的强度和韧性等于或高于常规回火材料的强度和韧性，例如，通过指定中碳钢中诸如Ti和Zr等氧化物形成元素的含量并结合氧化物晶粒和具有特定晶粒尺寸的氧化物和MnS的复合体。组成：一种中碳硬钢，其成分按重量比计为0.10-0.60％C，0.01-3.00％Si，0.20-3.00％Mn，0.01-0.30％S，0.03.0.30％V，0.005 -0.060％N，0.001-0.100％Ti，0.001-0.100％Zr，0.001-0.200％Hf，0.001-0.150％Y，0.001-0.150％La，0.001-0.150％Ce，0.001-0.050中的一种或多种％的Ca，和0.001-0.010％的Mg，其余的Fe具有不可避免的杂质。此外，以1×10 3〜1×10 6个/ mm 3掺入0.1〜10μm粒径的氧化物的晶粒和氧化物与MnS的复合体。此外，将Al和P的含量分别限制为≤0.005％和≥0.03％。通过该方法，可以在避免回火处理的必要性的同时，获得在热锻状态下具有优异的强度和韧性的钢。
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