| 摘要 |
A drill bit including a bit body having an upper end adapted to be detachably secured to a drill string and at least one leg at its lower end, each leg having a downwardly and inwardly extending journal bearing, at least one roller cone mounted on each journal bearing, at least one cutting element disposed on the at least one roller cone; and a hardfacing overlay on at least a portion of at least one of an inner surface of the at least one roller cone and a surface of the journal bearing, wherein a composition of the hardfacing overlay proximate an outside surface of the hardfacing overlay is different from a composition of the hardfacing overlay proximate an interface between the hardfacing overlay and the at least a portion of at least one of the inner surface of the at least one roller cone and the surface of the journal bearing is disclosed.
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