Wednesday  |  Allegheny  |  02:30 PM–02:50 PM

#13510, Time-Dependent Dynamic Behavior of Wrought and AM 17-4 PH SS at Elevated Temperatures

Precipitation-hardenable stainless steel alloy 17-4 (17-4 PH SS) can exhibit a wide range of strengths depending on the aging heat treatment. Maximum hardness (strength) occurs after aging for 1 hour at 480 °C, which produces nanoscale, Cu-rich precipitates throughout the microstructure. During machining and other dynamic plastic flow events, adiabatic heating can cause temperatures to reach the aging point in a few milliseconds. Therefore, it is necessary to characterize the influence of precipitation kinetics on thermal softening in 17-4 PH SS to accurately model its behavior under dynamic loading to large strains. Precipitation kinetics data are measured for wrought and an additively-manufactured 17-4 PH SS near the peak aging temperature with heating times ranging from 0.25 s to 1 h. The data are used to quantify the effect of precipitate growth on the thermal softening behavior observed in rapidly-heated dynamic compression tests, where heating times are on the order of seconds. Results show that a significant amount of precipitation growth (hardening) occurs within a few seconds of aging in both wrought and AM materials, meaning that even rapidly-heated dynamic data will underestimate the thermal softening of this alloy under real machining conditions. The thermal softening behavior of AM 17-4 PH SS in the stress-relieved condition differs from wrought material due to partial aging during the build and/or stress relief process, and perhaps due to additional strengthening precipitates in this material.

Steven Mates   National Institute of Standards and Technology
Saadi Habib   National Institute of Standards and Technology