Abstract
The mechanical properties ofa new line-pipe steel containing 0·45% V are strongly dependent upon the ability of the V to influence transformation characteristics in addition to providing strengthening from precipitation of V(CN). The V addition depresses the bainite start temperature and in this respect is similar to Mo. It is also shown that, although V increases the ferrite start temperature, it stabilizes the high-C austenite remaining at the end of the ferrite reaction. This stabilized austenite subsequently transforms to a martensite–bainite (M–B) constituent which is responsible for the continuous yield behaviour in a tensile test. The volume fraction of the M–B phase is strongly affected by the extent of interphase precipitation of V(CN) concurrent with ferrite formation and factors which increase the amount of interphase precipitation, such as N content, cause a reduction in the amount of M–B phase.
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