稀土镧对低合金高强钢微观组织及冲击韧性影响

Effect of Lanthanum on the Microstructure and impact toughness of HSLA Steel

摘要:

为了研究清楚稀土微合金化对低合金高强钢冲击韧性影响的机理，利用仪器化冲击试验机对实验钢进行了示波冲击实验。并通过扫描电镜、电子背散射衍射和X射线分析了稀土对低合金高强钢微观结构的影响，包括：组织、晶界特征和残余奥氏体的量。同时采用物理化学相分析和X射线小角度散射技术分析了稀土元素的固溶量及对低合金高强钢中铌钒钛元素析出量及其第二相粒子粒度分布的影响。结果表明，稀土镧可以提高低合金高强钢的冲击功，尤其是在裂纹的扩展阶段，主要原因归结为增加了残余奥氏体的量、增加了大角度晶界尤其是低Σ值晶界的量、减少了第二相粒子的析出量和细化了第二相粒子的尺寸。

关键词:稀土镧，低合金高强钢，冲击韧性，微观结构，第二相粒子

Abstract:

In order to research the mechanisms of effect of rare earth microalloying on the impact toughness of HSLA steel, oscillographic impact experiments have been tested by instrumented Charpy impact equipment. The microstructures including: tissues, characteristics of grain boundaries and volume fractions of the retained austenite have been analyzed by scanning electron microscopy (SEM), electron back scattering diffraction (EBSD) and X-ray diffraction (XRD). The solid solution quantity of lanthanum and precipitates of the niobium, titanium and vanadium were quantified by physics-chemical phase analysis. Sizes of the secondary phase precipitates were measured by small angle X–ray scattering (SAXS). The results indicated that, the toughness of the HSLA steel can be enhanced by addition of La into the steel, in particular to prevent cracks propagation. The mechanisms were as follow, the volume fraction of retained austenite, the quantity of high-angle and the low-Σ value coincidence site lattice (CSL) grain boundaries were increased. In addition, precipitates of niobium, titanium and vanadium were decreased and the sizes of the secondary phase precipitates were refined by addition of La into the steel.

Key words:Lanthanum; HSLA Steels; Impact Toughness; Microstructures; Second Phase Precipitates