The invention relates to a preparation method of gear steel, in particular to a bar for a large
wind driven generator gear and a manufacturing method of the bar. The bar comprises the following components of: 0.37-0.42 percent of C, 0.15-0.40 percent of Si, 0.80-1.25 percent of Cr, 0.50-0.90 percent of Mn, 0.15-0.30 percent of Mo, not more than 0.015 percent of S, 0.02-0.04 percent of Al, not more than 0.0015 percent of O, not more than 0.00020 percent of H, not more than 0.012 percent of P and the balance of Fe and unavoidable impurities. The manufacturing method comprises the steps of: adopting EAF (
Electric Arc Furnace) and LF (
Low Frequency) refining and VD (Vacuum Degassing)
smelting, controlling aim carbon, aim
phosphorus and tapping temperature of the
electric arc furnace, adding synthetic
slag, silicomangan and compound medium aluminum in a
ladle in the tapping process for pre-deoxidizing; carrying out
argon stirring in a refining process, fully deoxidizing, desulfurizing, removing impurities; treating for at least 10min under the vacuum degree of less than 0.5
torr of a VD furnace, feeding an Al wire after the vacuum is broken to control the content of the Al in the steelto be between 0.02 percent and 0.04 percent; and executing full-protection and low superheat degree pouring on
continuous casting, adopting a medium-strength soft-pressing process on the solidified
tail end, and adopting a heavy-pressing for carrying out rolling. The bar disclosed by the invention has high purity and compactness, and adapts to a complex and severe
working environment of a
wind power gear.