稀土对高强IF钢退火过程中的第二相析出行为的影响

以不同稀土含量的440 MPa高强IF钢为研究对象,在盐浴炉中模拟现场的连续退火,退火温度810℃,分别保温30 s、60 s,通过TEM与XRD对退火后的试样进行第二相分布、形状及成分分析,以研究稀土对高强IF钢第二相析出行为的影响。实验结果表明,保温时间基本不影响第二相的析出;不加稀土的高强IF钢析出的第二相呈弥散分布,且尺寸大小均匀,均在30 nm以下;加了稀土的高强IF钢析出的第二相分布在晶界处,并且伴随着团聚的现象,第二相尺寸不均匀,大颗粒在30 nm^100 nm之间;不加稀土的试验钢在810℃保温60 s下的析出相种类有FeTiP、TiC、TiN、NbN。实验结果为440 MPa高强IF钢在退火条件下第二相析出奠定了理论基础。

Effect of Rare Earth on Precipitation Behavior of Second Phase in High Strength IF Steel Annealing

The 440 MPa high-strength IF steel with different rare earth content was used as the research object,and the continuous annealing in the field was simulated in a salt bath furnace. The annealing temperature was 810 ℃, and holding time was 30 s and 60 s respectively. The second phase distribution, shape and composition analysis of the annealed sample were performed by TEM and XRD to investigate the influence of rare earth on the precipitation behavior of the second phase of high strength IF steel. The experimental results show that the holding time basically does not affect the precipitation of the second phase;the second phase precipitated by high-strength IF steel without rare earth shows a dispersion distribution, and the size is uniform, all below 30 nm;the high-strength IF steel with rare earth is precipitated.The second phase is distributed at the grain boundary, and along with the phenomenon of agglomeration, the size of the second phase is non-uniform, and the large particles are between 30 nm and 100 nm. The precipitated phases of test steels without RE annealed at 810 ℃ for 60 s include FeTiP, TiC, TiN and NbN. The experimental results lay a theoretical foundation for the precipitation of the second phase in the annealing condition of 440 MPa high strength IF steel.