Nb-V低碳微合金钢等温淬火过程析出行为

Precipitation behavior of carbides in Nb-V HSLA steel during isothermal quenching process and its strengthening effect were studied using TEM and nanoindentation tests. The results indicated that interphase precipitations and dispersed precipitations could occur simultaneously in the specimen treated at 700℃ for 60 min, while in other specimens, only random precipitations were observed. This phenomenon can be explained by mass balance criterion and ledge mechanism during diffusional phase transformation. It was also found that the average hardness of the specimen held at 600℃ for 20 min was 3.87 GPa and was 4.10 GPa at 650℃ for 20 min. Moreover, the TEM results illustrated that carbide precipitations in the specimen holding at 650℃ for 20 min were dispersed more uniformly and the volume fraction of the precipitations was greater than that treated at 600℃ for 20 min. The strengthening contributed by the precipitations was 110 MPa in the specimen treated at 650℃ for 20 min, evaluated by the Ashby-Orowan mechanism.