| 摘要 |
PURPOSE:To obtain a high-strength low-carbon steel material having superior heavy workability by forming a bainite, martensite or bainite-martensite mixed structure as the structure of a low-carbon steel, carrying out austenitizing by heating, and cooling the steel under specified conditions. CONSTITUTION:A bainite, martensite or bainite-martensite mixed structure in which the grain size of former austenite is <=35mum is formed as the structure of a low-carbon steel having a composition consisting of, by weight, 0.01-0.3% C, <1.5% Si, 0.3-2.5% Mn and the balance Fe with inevitable impurities. Austenitizing is then carried out to >=about 20% austenite content by heating the steel to the Ac1 point - the Ac3 point, and the steel is cooled to ordinary temp. -500 deg.C at 40-150 deg.C/sec average cooling rate. |
