Specimen size effects on ductile–brittle transition temperature in Charpy impact testing

One key issue for small specimen test techniques is to clarify specimen size effects on test results. In consideration of size effects on determining the ductile-to-brittle transition temperature (DBTT) in Charpy impact testing, a method to evaluate the plastic constraint loss for differently sized Charpy V-notch (CVN) specimens is proposed and applied to a ferritic–martensitic steel, 2WFK, developed by JNC. In the method, a constraint factor, α, that is an index of the plastic constraint is defined as α=σ∗/σy∗. Here, σ∗ is the critical cleavage fracture stress which is a material constant and σy∗ is the uniaxial yield stress at the DBTT at the strain rate generated in the Charpy impact test. The procedures for evaluating each of σ∗ and σy∗ are described and a result of σ∗ and σy∗, thus the value of α, is presented for different types of miniaturized and full-sized CVN specimens of 2WFK.