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.
Highlights
High strength, quenched and tempered steels have been largely used since decades for manufacturing of off-shore drilling parts and many components of automotive gearboxes
Up to rather high temperatures, fracture surfaces of microstructure M showed many coarse cleavage facets corresponding to upper bainite; cleavage facets of martensite, which dominated the lower temperature fracture surfaces appeared much finer due to the intricate microtexture of martensite variants
Two microstructures P and M taken from the same bar of a high strength quenched + tempered martensitic steel were study by instrumented Charpy tests and tensile tests on double-side notched plane strain specimens
Summary
High strength, quenched and tempered steels have been largely used since decades for manufacturing of off-shore drilling parts and many components of automotive gearboxes. High yield strength and good impact toughness are required as design criteria for such applications. As reviewed by e.g. Beranger et al [1], improving strength of these steels generally implies decreasing their impact toughness. The mechanical properties of this steel can be tuned by improving their final heat treatment [2]. An increase in tempering temperature is shown to increase impact toughness in the upper self-energy (USE) range, yet at the expense of yield strength. Improving the trade-off between these two mechanical properties is required to optimize in-service properties of components. The two microstructural components that have to be optimized in this way are (i) the martensitic matrix and (ii) the population of carbides that are formed during tempering
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
