Identification of ductile to brittle transition temperature by using plane strain specimen in tensile test and correlation with instrumented Charpy impact test: experimental and numerical study

¹ MINES ParisTech, PSL Research University, MAT - Centre des matériaux, CNRS UMR7633,  BP 87, 91003 Evry cedex, France
² ASCO Industries − Centre de Recherche CREAS, BP 70045, Avenue de France, 57301 Hagondange cedex, France

^* e-mail: frank.tioguem-teagho@mines-paristech.fr

Received: 12 May 2017
Accepted: 13 October 2017

Abstract

This study addresses the correlation between the ductile-to-brittle transition temperature ranges of high strength 4140 steel obtained respectively from tensile tests under plane strain (PS) conditions and from conventional Charpy impact tests. Specimens were taken respectively at 25 mm (P) and at 55 mm (M) from skin of a cylindrical 90-mm-radius hot rolled bar water quenched from 875 °C, tempered at 600 °C and air cooled. P and M samples respectively showed a fully martensitic and a martensite-bainite microstructure. Fracture surface observations showed good agreement for physical fracture mechanisms (cleavage facet size, mixed ductile + brittle fracture in the transition region, ductile fracture at higher temperatures) between PS and Charpy, in particular sensitivity of upper bainite to cleavage fracture that reduces fracture energy in the lower self-energy on Charpy tests.