Optimization of Step Times for ASTM F1624 Methodology Applied to Small Punch Tests in Aggressive Environments

Abstract

Threshold stress in aggressive environments is usually determined by tests under constant load, which are very time-consuming, so the incremental loading technique published in the ASTM F1624 standard was created to solve this issue. This approach has been recently applied to Small Punch tests, but it requires an optimization of the incremental step times, which is carried out in this work. Three medium- and high-strength quenched and tempered steels of 35, 50 and 60 HRC are exposed to three different cathodic polarization environments of 1, 5 and 10 mA/cm2 in 1N H2SO4 acid electrolyte with a Platinum anode, studying in each case three different step durations of one-quarter, one-sixth and one-eighth of the ones indicated in ASTM F1624. Optimal step times for Small Punch tests are derived from this work as one-sixth of the ones recommended in ASTM F1624 for tensile specimens, which are 20 min and 40 min for steps 1–10 and 11–20, respectively, in the case of 33 ≤ HRC < 45 steels, 10 min and 20 min for steps 1–10, 11–20 in the case of 45 ≤ HRC < 55 steels, and 10 min for steps 1–20 in the case of HRC ≥ 55 steels.

Keywords

• threshold stress
• small punch test
• constant load steps