稀土镧对低合金高强钢微观组织及冲击韧性的影响

Effect of Lanthanum on the Microstructure and Impact Toughness of HSLA Steel

为研究稀土微合金化对低合金高强钢冲击韧性的影响机理,利用仪器化冲击试验机对实验钢进行了示波冲击试验。并通过扫描电镜(SEM)、电子背散射衍射(EBSD)和X射线衍射(XRD)分析了稀土对低合金高强钢微观结构的影响及组织、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,稀土镧增加了低合金高强钢中残余奥氏体的量、增加了大角度晶界尤其是低Σ值晶界的量、减少了第二相粒子析出量并细化了第二相粒子的尺寸。因此,增加了裂纹扩展的阻力,提高了冲击韧性。

In order to research the mechanism of effect of rare earth micro-alloying on the impact toughness of HSLA steel, oscillographic impact experiments were performed by instrumented Charpy impact equipment. The microstructures, characteristics of grain boundaries and volume fractions of the retained austenite were 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 indicate that La addition increases the volume fraction of retained austenite and the quantity of high-angle,especially the low-Σ value coincidence site lattice（CSL） grain boundaries, decreases the precipitates of niobium, titanium and vanadium and refines the sizes of the secondary phase precipitates; as a result, crack propagation is prevented and the toughness of the HSLA steel is enhanced.