Production manner null of non heat treated steel and its bar amp; part for high tenacious hot forging

摘要

PURPOSE:To obtain the non-heat treated steel and bar steel for hot forging having excellent strength and toughness, at the time of subjecting a molten steel contg. specified amounts of Mn, Cr, V and Ti to continuous casting, by regulating its cooling in a specified temp. range, executing casting and thereafter directly rolling the steel into a bar steel. CONSTITUTION:A steel constituted of, by weight, 0.20 to 0.60% C, 0.10 to 2.00% Si, 0.50 to 2.00% Mn, 0.10 to 1.20% Cr, 0.03 to 0.20% V, 0.005 to 0.070% Ti, 0.005% Al, 0.0010 to 0.0100% O, 0.005 to 0.020% N and the balance Fe with inevitable impurities is subjected to continuous casting. The casting is executed under the condition that =20 deg.C/min cooling rate is regulated in the temp. range from its solidifying temp. to 1000 deg.C. After that, the steel is directly rolled into a bar steel without executing blooming. The bar steel is heated to about =1270 deg.C and is forged into machine parts. After that, the machine parts are cooled in the temp. range of about 800 to 400 deg.C at 0.1 to 5.0 deg.C/sec average. The bar steel has excellent impact properties as hot-forged state and is useful as a non-heat treated steel for hot forging.