Optimized Heat Treatment for NIST Certified Low-Energy Charpy Specimens to Be Tested at 21 °C

Published

July 11, 2024

Author(s)

Enrico Lucon, Allen Eckhardt, Raymond L. Santoyo

Abstract

The NIST Charpy Machine Verification Program has recently decided to change the test temperature for low-energy and high-energy certified reference specimens from -40 °C to 21 °C. Consequently, low-energy specimens currently tend to remain in the impact zone after fracture, with an increased risk of jamming or multiple secondary collisions between broken halves and various machine parts. Both occurrences artificially increase absorbed energy, and their likelihood should be minimized. In the study presented here, we investigated the effect of changing the final tempering temperature (Ttemp) of low-energy specimens, with the aim of decreasing their room temperature impact toughness, and therefore lowering the chance of jamming/multiple collisions to acceptable levels (close to zero). It was found that decreasing Ttemp from 371 °C/700 °F (current heat treatment) to 316 °C/600 °F basically duplicates at 21 °C the testing conditions (absorbed energy and post-fracture kinetics) previously observed at 40 °C.

Citation

NIST Interagency/Internal Report (NISTIR) - 8531

Report Number

8531

NIST Pub Series

NIST Interagency/Internal Report (NISTIR)

Pub Type

NIST Pubs

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Keywords

Certified Charpy specimens, NIST Charpy Machine Verification Program, post-fracture kinetics, specimen jamming, tempering temperature.

Citation

Lucon, E. , Eckhardt, A. and Santoyo, R. (2024), Optimized Heat Treatment for NIST Certified Low-Energy Charpy Specimens to Be Tested at 21 °C, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=958193 (Accessed October 13, 2025)