Assessing the Quality of As-Received 4340 Steel for the Production of NIST Charpy Reference Specimens
Enrico Lucon, May Martin
The Charpy Machine Verification Program at NIST in Boulder uses heat-treated 4340 steel for the production of indirect verification Charpy specimens at low- and high-energy level. Recently, a batch of steel purchased for the program turned out to be unacceptably inhomogeneous, causing several NIST Contractors to produce specimen lots that did not fulfil our variability requirements, despite repeated attempts at modifying the heat-treatment process. The whole batch of steel had to be eventually scraped. In order to avoid such an occurrence in the future and develop an investigation procedure that can detect variability issues in the acceptance phase of newly purchased batches of 4340 steel, we have performed the following investigations and measurements on samples from "good" and "bad" heats: hardness measurements (Rockwell C and Vickers), instrumented Charpy tests, optical investigations, and texture analyses (including grain size measurements). Of all the parameters considered, we found that grain size can clearly differentiate between acceptable (30 µm – 40 µm) and unacceptable (60 µm – 70 µm) heats, and should therefore become the basis of future heat quality assessments. In support, hardness measurements can also be performed, while Charpy tests are not recommended in view of their relative experimental and economic burden.
and Martin, M.
Assessing the Quality of As-Received 4340 Steel for the Production of NIST Charpy Reference Specimens, Technical Note (NIST TN), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.6028/NIST.TN.2177, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=933129
(Accessed October 26, 2021)