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l,  and Höganäs AB, SE 263 83 Höganäs, SWEDEN; ABSTRACT. A detailed 3D crack walk study is made on Ni-Cu alloyed PM steel withMo pre-alloyed base powder. Surface crack walk has earlier been observed not to passthrough islands of Ni-rich austenite. The aim of the study is to find the crack walk inrelation to the Ni-rich austenite. Successive grinding in steps of about 20 mm is madeand the surface crack in each level is recorded by light optical microscope. The mainpart of the crack walk is found through high temperature bainite or along the interfacebetween martensite and high temperature bainite. Ni-rich austenite is surrounded bymartensite that hinders the crack to enter into austenite. The result indicates thataustenite as such is not a strong crack stopper.