Susceptibility to Embrittlement of 4 Ni-CrMo High Strength Steels and 11 Cr-NiMoV Heat-Resistant Steel-Roles of Melting Methods and Residual Elements

摘要

The security of turbine componentscritically depends on their fracture toughness afterlong time of service exposure at temperature, andhence on the brittle-ductile transition temperatureafter in service embrittlement. These characteristicsdepend at the same time on the initial quality of thesteel, and on its susceptibility to embrittlement.On two 4Ni-CrMo high strength low alloy steels (0.35C3.8Ni 1.7Cr 0.25Mo and 0.30C 3.7Ni 1.25Cr 0.40Mo) andone heat-resistant 11%Cr-NiMoV grade, differentlevels of initial fracture toughness quality have beenachieved by varying the method of melting (with andwithout consumable electrode remelting) andindependently by varying the amount of residualelements. The embrittlement susceptibility isevaluated by testing after a Step-Cooling heattreatment. The results are discussed by trying tohighlight the role of the initial quality, theintrinsic susceptibility of the grade toembrittlement, and the level of residual elements.