| 摘要 |
PROBLEM TO BE SOLVED: To attain a specification for improving durability as the whole ball screw device 1, by restraining surface starting point type separation. SOLUTION: Respective balls 4 and 4 are made of steel including C by 0.3-1.2 mass%, Si by 0.3-2.2 mass% and Mn by 0.2-2.0 mass%. The nitrogen concentration of its surface is set at 0.2-2.0 mass% by carbonitriding processing or nitriding processing, and the area ratio of Si-Mn-based nitride including Si and Mn is set at 1%-less than 20%. A residual austenite quantity of a surface part of an outer diameter side ball screw groove 6 is set atγ<SB>ro</SB>volume%, and a residual austenite quantity of a surface part of an inner diameter side ball screw groove 5 is set atγ<SB>ri</SB>volume%, and assuming the residual austenite quantity of a rolling surface of the respective balls 4 and 4 asγ<SB>rb</SB>volume%, 0≤γ<SB>ro</SB>,γ<SB>ri</SB>,γ<SB>rb</SB>≤50 is satisfied, andγ<SB>ro</SB>-15≤γ<SB>rb</SB>≤γ<SB>ro</SB>+15 andγ<SB>ri</SB>-15≤γ<SB>rb</SB>≤γ<SB>ri</SB>+15 are also satisfied. COPYRIGHT: (C)2009,JPO&INPIT
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