Development of high-strength and heat-resistant steel for the SCWR type VVER’s
Keywords: VVER-SKD, supercritical coolant parameters, high-strength vessel steel, super-clear steel, microalloying, modification, radiation resistance, heat resistance, thermal embrittlement.
Improving the efficiency and safety of nuclear energetics is only possible with the commissioning of nuclear reactors of promising projects with increased thermal efficiency, improved fuel efficiency, increased service life. One of the most promising variants of ones are are vessel type water cooled reactors with supercritical coolant parameters.
The increased mechanical load and elevated operating temperature set new requirements for the level of strength and heat resistance of vessel steelsl.
For projects supercritical VVER highly reliable and high-resource vesselss, work was undertaken on the development of innovative vessel steel with high complex of service and technological properties.
To achieve the highest level of strength properties while maintaining or improving visco plastic properties should be optimized steel structure at all levels (mega-meso, micro and nano) and the use of all three strengthening mechanisms (solid solution strengthening, structure and substructure strengthening, dispersion strengthening), while maintaining a significant degree of reference in composition and manufacturing techniques.
The main ways of improving the properties of the steel have been taken:
I. Transition to the lower bainite, martensite – bainite or martensitic structure of steel.
II. The most effective use of precipitation strengthening.
III. Getting superfine austenite grain.
IV. Optimization of the composition on the basic alloying elements with regard to their influence on the strength and visco-plastic properties, resistance to neutron exposure and heat embrittlement.
V. Improving metallurgical quality of steel - reduction of deteliorating and trace elements, to reduce the harmful effect of non-metallic inclusions and all types of inhomogenity.
VI. Microalloying and modification.
Steels of system Cr-Ni-Mo-V w. nickel content of 2.5 to 6.5% and 3Cr-3W- (Mn) -0.25V- ( Ta):prospective vessel materials were investigated.
According to the results of the most promising have been chosen high-nickel steels, containing from 2.5 to 5% Ni.
Developed innovative steel provides strength level of KP 70+ category at 400C, it has a critical temperature of brittleness in the range of minus 125 - minus 165C and provides a resource of the reactor vessel more, than 120 years.
Achieved strength properties at a temperature of 600C (KP 50) allow to raise the issue of the development of steel for uncooled vessel, operating at a temperature of the coolant.
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