高强度油井管用钢带状偏析及其条带型混晶现象研究

Banded segregation and its related band-typed mixed grain structure in high strength oil well pipe steel

带状偏析组织是影响高强钢服役过程抗腐蚀性能的重要缺陷之一。为了深入揭示轧材中常见的碳化物带状缺陷组织特征,以C110级高强度油井管钢为对象,针对源于铸坯点状偏析的管材带状组织,利用OM、SEM、EDS、EPMA等手段,研究了其热轧材及其调质处理过程不同环节下的晶粒大小分布行为。发现了一种与碳化物带状缺陷相关联的条带型混晶组织。其组织中基体区域晶粒明显粗大,偏析带区域晶粒则相对细小,呈现出与带状组织相似的粗细晶粒相间结构。基于EPMA分析,揭示了带状组织中元素偏析程度与其晶粒尺度的关联性,并利用溶质拖曳理论与第二相粒子钉扎作用解释了合金元素对晶粒生长的影响。

Banded segregation is one of major defects to affect the corrosion resistant performance of high strength steels. To reveal and understand the characteristics of a typical carbide banded structure in rolled steels, C110 grade oil casing steel was studied by aiming at the banded structure in its tube product, which is specially originated from the as-cast spot like segregation. The grain sizes and their distribution were studied experimentally at its various hot working stages by means of OM, SEM, EDS and EPMA. A kind of band-typed mixed grain structure was observed in the tube wall, in which coarse grains exist in the banded substrate area, while the much finer grains exist in the banded segregation area. It is shown that quench and tempering heat treatments can only improve the homogeneity of the grain sizes to a very limited extent. By EPMA analysis, the relationship between elemental segregation and grain size in the microstructurally banded region was revealed. And the mechanism of the unusual mixed grain structure behavior was explained through solute drag theory together with the pinning effects of the precipitated second phase particles.