US 11,898,231 B2
Steel for gear and method for manufacturing gear using the same
In Beom Lee, Goyang-si (KR); Min Woo Kang, Yongin-si (KR); Min Woo Kang, Incheon (KR); Dong Hwi Kim, Yongin-si (KR); Chang Won Kang, Hwaseong-si (KR); Myung Sik Kim, Daegu (KR); Sung Min Hong, Seoul (KR); Gung Seung Nam, Cheonan-si (KR); and Sang Won Lee, Asan-si (KR)
Assigned to HYUNDAI MOTOR COMPANY, Seoul (KR); KIA CORPORATION, Seoul (KR); and HYUNDAI STEEL COMPANY, Incheon (KR)
Filed by HYUNDAI MOTOR COMPANY, Seoul (KR); KIA CORPORATION, Seoul (KR); and HYUNDAI STEEL COMPANY, Incheon (KR)
Filed on Apr. 19, 2021, as Appl. No. 17/234,428.
Claims priority of application No. 10-2020-0121558 (KR), filed on Sep. 21, 2020.
Prior Publication US 2022/0090244 A1, Mar. 24, 2022
Int. Cl. C22C 38/48 (2006.01); C22C 38/44 (2006.01); C22C 38/46 (2006.01); C21D 7/13 (2006.01); C22C 38/04 (2006.01); C21D 9/32 (2006.01); C21D 8/00 (2006.01); C22C 38/02 (2006.01)
CPC C22C 38/48 (2013.01) [C21D 7/13 (2013.01); C21D 8/005 (2013.01); C21D 9/32 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/44 (2013.01); C22C 38/46 (2013.01)] 8 Claims
OG exemplary drawing
 
1. 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.