Thermomechanical controlled processing to achieve very fine grains in the ISO 5832-9 austenitic stainless steel biomaterial

摘要

Simulations of thermomechanical processing of a high niobium- and nitrogen-bearing austenitic stainless steel for orthopedic implants (ISO 5832-9) were conducted using hot torsion test with multiple deformations under continuous cooling conditions. Samples were reheated to 1250 °C and subjected to deformation schedules with pass strain of 0.3, strain rate of 1 s- 1 and interpass times of 5, 20 and 50 s. Optical microscopy, TEM, EDS and EBSD were used to characterize the samples. Characterization of precipitates indicated that only TiNbN was undissolved after soaking, while Z-phase and NbN precipitated during on cooling deformation schedules. The evolution of grain and precipitate sizes with deformation conditions were studied and related to both grain refinement, and mechanical behavior observed. The critical grain size limited by precipitates was calculated using the values obtained for size and volume fraction of precipitates. Differences observed between calculated and measured values were discussed.