Steel for gear and method for manufacturing gear using the same

A method for manufacturing a gear, the method comprising:

• a molten metal preparing step of preparing a molten metal consisting of, based on a total weight thereof:
• C:
• 0.10-0.30 wt %;
• Si:
• 0.60-0.80 wt %;
• Mn:
• 0.25-0.75 wt %;
• Cr:
• 1.80-2.20 wt %;
• Ni:
• 0.50-1.50 wt %;
• Mo:
• 0.20-0.40 wt %;
• Nb:
• 0.025-0.050 wt %;
• V:
• 0.030-0.050 wt %;
• and a balance of Fe and inevitable impurities, wherein contents of Nb and V satisfy the following <Relationship Formula 1>:
• 0.055<[Nb]+[V]<0.100 <Relationship Formula 1>,
• wherein [Nb] represents a content of Nb and [V] represents a content of V;
• a pre-rolling heat treatment step of casting molten metal and then thermally treating the cast molten metal;
• a rolled steel rolling step of rolling the thermally treated cast molten metal into a rolled steel;
• a forged steel forging step of forging the thermally treated, rolled steel into a planetary gear;
• a forged steel heat treatment step of thermally treating the forged steel;
• an article processing step of processing the forged steel into a final article;
• and
• a carburizing heat treatment step of carburizing the final article,
• wherein the final article after the carburizing heat treatment step has a MX precipitate formed at a fraction of 0.03-0.07% therein, the MX precipitate being 150 nm or less in size and amounting to 50 or more per 100 μm2.