A method using one or more of certain triazoles in an amount effective to reduce cobalt leaching during a metal working process from a metal working tool comprising cobalt, such as tungsten carbide particles bonded by cobalt, wherein the one or more triazoles comprise at least butyl-benzotriazole, and optionally one or more other benzotriazoles. Also, a composition is provided which comprises a metal working fluid and one or more of these triazoles in an amount effective to reduce cobalt leaching from metal working tools comprising cobalt, such as tungsten carbide particles bonded by cobalt.