| 摘要 |
PROBLEM TO BE SOLVED: To save energy by obviating a part of the production process for temper-rolled steel and further to improve the mechanical properties of the product. SOLUTION: A billet or the like of low carbon steel or medium carbon steel composed of C, Mn, Si, P, and the balance iron with inevitable impurities (inclusive of Cu, Ni and Cr, and their contents are controlled) is heated at a temp. of 1,200 to 1,300 deg.C, subjected to rolling, then immediately quench-hardened with cold water at a temp. of 800 to 900 deg.C and is reheated and tempered at a temp. of 500 to 600 deg.C after the cooling to produce temper-rolled steel for structural purpose. In this way, in the case of a low carbon steel, its yield point is controlled to 800 N/mm2, tensile strength to >=900 N/mm2, elongation to >=18%, Charpy to >=130 J/cm2 and Brinell hardness to >=285, and in the case of a medium carbon steel, its yield point and tensile strength are equal to those of the low carbon steel, and its elongation is controlled to >=15%, Charpy to >=90 J/cm2 and Brinell hardness to >=290.
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