High cycle fatigue performance and corresponding fracture behaviors of GH4169 studs formed by thread warm rolling process

Threaded components like bolts and studs, are prone to fatigue failures due to high stress concentration. GH4169 superalloy widely used in the aerospace field has excellent mechanical properties in high temperature environment and is ideal for high strength thread fasteners. In this study, the thread warm rolling process is developed to prepare GH4169 studs samples with enhanced fatigue performance. Firstly, the configuration of the rolling apparatus is introduced and described. Then, thread forming experiments are conducted on GH4169 matrix by use of the thread warm rolling process and traditional thread turning process respectively. The fatigue performance and mechanical properties of these formed studs are evaluated. Compared to the turning process, surface finish of thread root is further improved from R_a 0.26 to R_a 0.13, and increased microhardness distributed in the severe plastic deformation (SPD) layer are achieved for thread warm rolling process. The warm rolling process induces the SPD layer depth of approximately 80–100 μm at the thread root, significantly enhancing mechanical properties here and improving fatigue performance of overall parts. High cycle fatigue tests demonstrate that GH4169 studs formed by warm rolling process exhibit a fatigue life about 25 times greater than those formed by turning process.