抄録
In this study, effects of bainite structure on high-temperature strength, precipitation and aggregation behaviors of carbides during tempering are investigated for 0.2C-3Cr-W-Mo-V-Co steel comparing with martensite structure obtained by particularly rapid quenching.
The results obtained are as follows :
(1) During cooling from austenitized temperature at the rate lower than the rate of half temperature time being 10 min, granular upper bainite structure, without carbide precipitation in boundary is obtained with about 15% stable retained austenite.
(2) During tempering of this structure,
(i) precipitation of M3C and transformation of M3C→M7C3 in situ are suppressed, while those phenomena take place in martensite tempering,
(ii) boundary precipitation and aggregation of M6C are suppressed until higher tempering temperature because of the rarer distribution density of bainite grain boundary than martensite lath boundary, and through above (i), (ii),
(iii) increasing of volume of MC, M2C precipitated, their homogeneous distribution and suppressing of aggregation of them, which are all effective to the strengthening of the steel, are promoted.
(3) As the results, this upper bainite structure shows excellent high-temperature strength, compared with martensite structure.
