高氮奥氏体钢中退火孪晶界及其断裂刻面的特征

Characteristics of Annealing Twin Boundary and its Fracture Facet in a High-nitrogen Bearing Austenitic Steel

用光学显微镜和扫描电镜对18Cr18Mn0.7N高氮奥氏体钢固溶处理后的退火孪晶界及低温脆断中的退火孪晶界断面进行了观察和分析。结果表明,高氮奥氏体钢固溶处理时形成大量退火孪晶,退火孪晶界上存在微米高度的台阶,同一退火孪晶界上的台阶可以合并和分解,取向也在不断变化。退火孪晶界断面上存在折线状台阶花样,折线的首、末两端均位于断面边缘即晶界上;每根折线由三根取向不同的直线段依次圆滑连接而成,每根直线段分别与一组形变迹线平行,而相邻直线段间成120°角;数根折线以晶界上的同一点为圆心,形成一组同心半圆形花样,断裂刻面上的这种折线状台阶可作为退火孪晶界断裂刻面的判断依据。

Characteristics of annealing twin boundaries in solution treated specimens and their fracture facets on low-temperature brittle fracture surfaces in an 18Cr-18Mn-0.7N austenitic steel were investigated by means of optical and scanning electron microscopic observation. A great deal of annealing twins form during solution treatment, and there are many micron-scale steps on the annealing twin boundaries. These steps can either unite or disunite and their orientation changes constantly. Bent-line-form step patterns are observed on annealing twin boundary fracture facets. The bent lines originate from and end up at the facets border that is grain boundary. Each bent line is made up of three different orientation straight line segments connected one another by smooth curve, and the adjacent straight line segments make an angle of 120°. Moreover, each straight line segment parallels to one set of deformation trace. Several bent lines form a set of semicircles whose center situate in the same point on the grain boundary. The bent-line-form step patterns on the fracture facets can be taken for the determination criterion of annealing twin boundary fracture facets.