不锈钢管道焊接头的局部微观结构、硬度和机械性能

Local Microstructures,Hardness and Mechanical Propertiesof a Stainless Steel Pipe Welded Joint

完成了1Cr18Ni9Ti不锈钢管道对接焊接头母材、热影响区和焊缝金属三区域的局部微观结构、硬度和单调机械性能的详细试验研究。揭示了三区域存在明显差异 ,尤其是焊缝金属区的局部微观组织结构不均匀性和局部硬度、机械性能的分散性最大。说明了在结构分析中有必要考虑这种差异 ,并引入可靠性方法。此外 ,还揭示了由奥氏体基体 富δ铁素体带状结构组成的柱状晶是焊缝金属的特征微观结构 ,相邻富δ铁素体带的距离(40μm)恰好是该区域低周疲劳短裂纹行为中微观结构短裂纹(MSC)阶段和物理短裂纹(PSC)阶段的分界点。

An experimental investigation is carefully performed into the local microstructures,hardness values and monotonic mechanical properties of the three zones (the base metal,heat affecting zone and weld metal) of 1Cr18Ni9Ti stainless steel pipe welded joint.The local microstructures are observed by a metallurgical test and a surface replica technology,the local hardness values are measures by a random Vickers hardness test,and the local mechanical properties are characterized by the Ramberg Osgood and modified Ramberg Osgood stress strain relations.The investigation reveals that there are significant differences of the three zones in the local microstructures,hardness values and monotonic mechanical properties,especially of the three zones in the local microstructures,hardness values and monotonic mechanical properties,especially of the weld metal.The weld metal exhibits the largest heterogeneity of local microstructures and monotonic mechanical properties,and the largest scatter of local hardness values.It is necessary to consider these differences and introduce the reliability method to model the scatter in the pipe analysis.In addition,it is verified that a columnar grain structure,which is made up of matrix rich δ ferrite bands,can characterize the weld metal and the distance between the neighboring rich δ ferrite bands is an appropriate measurement of the columnar grain structure.This measurement is in accordance with the transition point between the microstructural short crack and physical small crack stages,which are generally used for characterizing the short fatigue crack behavior of materials.This indicates that the microstructure controls the fatigue damage character of the present material.