Detection of copper precipitates in 15 NiCuMoNb5 (WB 36) steel by using micromagnetic NDE techniques

The material investigations presented confirm the results of earlier investigatins with a conclusion that the service-induced hardening and decrease in toughness in WB 36 materials are caused by the precipitation of copper. In the initial state of the material, only a part of the alloyed copper is precipitated. The other part is still solved and can be precipitated during long-term operation at temperatures above 320°C to 350°C. The copper precipitation leads to a ditortion of the crystal lattice surrounding the copper precipitates and yields internal micro-stresses. If the number and size of the copper precipitates change during operation of a component, a change of the residual-stress level occurs. The results obained from load stress-related Barkhausen noise measurements demonstrate that these micro-magnetic procedures are generally suitable for the detection of copper precipitation.