Metal treatment – Stock – Carburized or nitrided
Reexamination Certificate
2005-11-22
2005-11-22
Yee, Deborah (Department: 1742)
Metal treatment
Stock
Carburized or nitrided
C148S230000, C148S231000, C148S208000
Reexamination Certificate
active
06966954
ABSTRACT:
A roller bearing that provides ball and roller bearing elements comprised of M50 steel and M50NiL steel having surface hardnesses above 60 HRC, and in the range of 65-72 HRC. The hardness in the surface region is achieved by nitriding the surface to achieve a high hardness and extended life. This improvement is brought about by controlling the microstructure of the alloy by minimizing the formation of retained austenite. The material is tempered as required. The surface is then nitrided, but the nitriding operation is carefully controlled to avoid the formation of intergranular nitrides. Because of the method used to prevent the formation of intergranular nitrides, some carbon may be present to prevent the surface of the steel from becoming depleted of carbon. The hardening element in this nitro-carburizing operation is nitrogen, which forms iron nitride as Fe3N or Fe4N intragranularly. The purpose of the carbon in the operation is to maintain the concentration of carbon in the surface of the bearing so that the properties are not altered by decarburizing the surface. Standard gaseous and plasma nitriding techniques also may be used for the nitriding operation.
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Johnson Michael Gilbert
Rhoads Mark Alan
Scheetz Jonothan Allen
General Electric Comany
Leppo Shawn K.
Maria Carmen Santa
McNees Wallace & Nurick LLC
Yee Deborah
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