At the time of hot forging production manner null of the hot forging non heat treated steel where system does not coarsen

摘要

PURPOSE:To manufacture a hot forged non-heat treated steel free from the coarsening of the structure as hot forged and excellent in strength and toughness by subjecting the molten metal of a low alloy steel having a specified compsn. to deoxidation treatment, and thereafter, furthermore executing forced deoxidation by Al, Ti or the like. CONSTITUTION:Molten steel from a steel-making furnace is deoxidized by C, Si, Mn, Fe-Si, Fe-Mn or the like or is furthermore deoxidized by a vacuum degassing apparatus or the like to reduce the amt. of dissolved oxygen to about 10 to 100ppm. After that, this steel is subjected to forced deoxidation by a strong deoxidizer constituted of Al, Ti, Zr or their alloy and is cast. The steel is cooled from the solidifying temp. to 1000 deg.C at =20 deg.C/min average cooling rate. The hot forged non heat treated steel contg., by weight, 0.01 to 0.60% C, 0.05 to 2.00% Si, 0.03 to 3.00% Mn, 0.04 to 0.20% S, 0.05 to 2.00% Cr, 0.03 to 0.30% V, 0.008 to 0.02% N and specified small amounts of one or more kinds of Al and Ti or Zr as well, contg. elements having the atomic number more than that of Hf and in which crystallized and precipitated products are finely dispersed can be obtd.