This paper describes part of an investigation into differences in cavitation characteristics in commercial and high-purity Cr-Mo-V steels of the types used in rotors and pipes in steam power plant....

The creep cavitation of commercial and high-purity Cr-Mo-V steels

Remaining creep life estimation by strain assessment on plant

Microstructural instability of 0.5Cr0.5Mo0.25V creep-resistant steel during service at elevated temperatures

Ferrite morphologies and carbide precipitate dispersions in a ½Cr-Mo-V creep-resisting steel have been studied after isothermal transformation at a number of subcritical temperatures in the ferrite and bainite ranges, and also after rapid quenching to room temperature to produce martensite. It has been found that VC precipitates by the interphase mechanism during direct transformation to ferrite, and towards the latter stages of the transformation, some fibres of Mo2C also form. Bainite morphologies ranged from granular at the higher transformation temperatures to lath-like at lower temperatures. Tempering of bainite and martensite at 700°C resulted in VC precipitation on dislocations and the interparticle spacing tended to decrease as the initial transformation temperature in the bainite range was increased. However, the best resistance to overageing during tempering was provided by ferrite produced by direct transformation at 700°C. These differences in dispersion stability are explained in term...

Ferrite morphologies and carbide precipitation in a Cr-Mo-V creep-resisting steel

The term pseudo-intercrystalline brittleness is proposed to describe a fracture mechanism which can occur in poly-crystalline alloys which contain a fine dispersion of a second phase. If narrow particle-free zones develop along grain boundaries, separation can occur after large amounts of plastic strain, which is highly localized to the vicinity of grain boundaries. Since the hardened grain interior does not contribute to plastic deformation the total plastic deformation to fracture and fracture toughness remain small. Quantitative models are proposed to interpret the micromechanism of fracture and to describe the grain-size dependence of fracture toughness. The fracture of precipitation hardening aluminum alloys, creep resistant and structural steels are discussed in terms of the models. Finally an interpretation of the mechanism of stress-relief cracking in steel weldments is given.

The mechanism of pseudo-intercrystalline brittleness of precipitation-hardened alloys and tempered steels

The performance of Cr-Mo-V steels, as widely used for steam pipe work, turbine rotors and casings, and associated bolts in steam power generating plant, may be limited by a susceptibility to failure at low ductility, especially when heat treated to high strength levels. To investigate the ductility in creep conditions of such steels, an extensive study of the interrelation of heat treatment, microstructure, creep strength, rupture strength, rupture ductility, and fracture characteristics has been made in commercially produced 0·5Cr-0·5Mo-0·25V and 1Cr-1 Mo-0·25V steels tested at 550°C for times up to >20000h. The results show that the rupture strength and ductility can be varied widely by changing the austenitizing temperature and the rate of cooling therefrom, and that a heat treatment at a high temperature (1300°C), given to simulate the microstructure in the vicinity of a weld, can produce very low creep-rupture ductility (<1%). Low ductility in these steels is associated with an intergranular ...

J. Williamson

Papers

Effect of heattreatment variations on strength and ductility of Cr-Mo-V steels during creep at 550°C