采用OM, SEM和TEM对V微合金化钢与V-N微合金化钢的组织与析出相进行了分析, 研究了强化机制. 结果表明, V微合金化钢与V-N微合金化钢的显微组织主要为铁素体与少量珠光体的混合组织. 随着卷取温度的升高, V-N微合金化钢的强度呈现出先增加后下降的规律, 600 ℃时获得了最优的力学性能, 其屈服强度与抗拉强度分别达到了605与687 MPa, 延伸率为24.5%. 与V微合金化钢相比, V-N微合金化钢的铁素体晶粒更细小, 平均晶粒尺寸达到4.5 mm, 析出相更细小弥散, 尺寸在3~50 nm之间, 平均尺寸达到8.0 nm, 以及更高的位错密度. 晶粒细化、析出强化与位错强化是V-N微合金化钢具有高屈服强度的主要原因, 其中细晶强化是最主要的强化机制, 占总屈服强度的43.05%, 析出强化与位错强化对屈服强度的贡献高达34.44%.

Automobile beam steel with high strength is the development trend of the automotive industry. With the development of heavy-duty vehicles, low cost automobile beam steel both with high strength and high toughness need to be developed. V-N microalloying method combined with thermal mechanical controlled process has a significant grain refinement function. Therefore, the relationship of different N content and technology should be studied in detail. In this work, the microstructure and precipitates of V and V-N microalloyed steel were investigated by using OM, SEM and TEM. And their strengthening mechanism was studied. The results show that both V microalloyed steel and V-N microalloyed steel mainly consist of ferrite and little pearlite. With the increasing of coiling temperature, the strength increased first and then decreased. The optimum mechanical properties were obtained when coiling at 600 ℃, the yield strength, tensile strength and elongation reached 605 MPa, 687 MPa and 24.5%, respectively. Compared with V microalloyed steel, the ferrite in V-N microalloyed steel present finer grain size which can be refined to about 4.5 mm. The precipitates were finer and more dispersed which distribute mainly between 3~50 nm and have the average size of 8.0 nm. And the dislocation density in V-N microalloyed steel is higher. Ferrite grain refinement strengthening, precipitation strengthening and dislocation strengthening make V-N microalloyed steel possess higher yield strength. Ferrite grain refinement strengthening is the predominant mechanism and contributes 43.05% to the yield strength. And the contribution of precipitation strengthening and dislocation strengthening to the yield strength is up to 34.44%.