A series of thermal treatments on typical WWER-1000 reactor pressure vessel steel has been carried out to induce phosphorus segregation. Two conditions have been achieved with significantly different ductile-to-brittle transition temperatures, when compared to untreated metal. Tensile properties, hardness and non-destructive techniques have also been investigated. This study confirms that when phosphorus segregation leads to embrittlement, which is directly detected by Charpy testing, owing to the non-hardening nature of the embrittlement mechanism, neither hardness nor the other applied non-destructive testing (thermoelectric, magnetic Barkhausen and positron annihilation) provide substantial indication of material degradation. The results obtained are important sources of information to understand the behaviour of materials for which phosphorus segregation might occur; in particular with regard to their sensitivity to fracture.