The paper represents the results of investigation of martensitic and austenitic steels and their development in manufacturing of steam pipes and heating surface for advanced ultra-supercritical (A-USC) power plants with service steam temperature up to 680 o C and pressure up to 32 MPa. There was shown that alloying by 3% Co of martensitic steels such as 9Cr-2W-Mo-VNb contributed to obtaining a high degree of dispersion of structure and improve creep resistance on 15-20% compared to steel type T/P92. Optimization of chemical composition and heat treatment parameters developed austenitic heat-resistant steel have provided a growth of long-term strength up to ~ 1.5 times (~ 96 N/mm2 at 680 o C, 10 5 h) in comparison with steels such as TP347. Steels were developed in manufacturing of parts of TPP equipment (headers, reheaters, steampipes etc.).
Dynamic structural changes during creep tests for about 103 hours at 600 and 650oC were investigated in a P92-type 9%Cr martensitic heat resistant steel. The structural changes are characterised by the development of relatively large equiaxed subgrains with relatively low dislocation densities in place of initial martensite laths. The coarsening of substructure was accompanied by a growth of second phase precipitates. The final grain/subgrain sizes and dislocation densities evolved after the creep tests were in rough correlation with applied stresses, i.e. larger (sub)grains developed under lower stresses. The structural mechanism responsible for microstructure evolution was considered as a kind of continuous dynamic recrystallization.
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