Abstract
The influence of microstructure on the fracture toughness of two industrially processed 1000 MPa dual-phase (DP) steel grades is investigated. Crack initiation and propagation resistance are evaluated by means of the essential work of fracture (EWF) methodology and the main damage and fracture mechanisms are investigated. The results are discussed in terms of the proportion and distribution of the different microstructural constituents, which is assessed by scanning electron microscopy (SEM), high-resolution electron backscatter diffraction (HR-EBSD) and nanoindentation hardness measurements. The investigations show that the strain-induced transformation of retained austenite to martensite (TRIP effect), may be detrimental to cracking resistance, even though it increases tensile properties. This phenomenon is attributed to a "brittle" network effect generated by the presence of hard fresh martensite islands in the fracture process zone. The connectivity of the hard secondary phases and the proportion of soft phase (ferrite) also have a major role in fracture toughness. The DP steel with the larger volume fraction of ferrite and homogeneously distributed martensite islands shows significantly higher crack propagation resistance. The contribution of necking to the ductile fracture process is evaluated by means of thickness measurements in fractured DENT specimens and the correlation between the specific essential work of fracture (we) and tensile properties is investigated. It is concluded that the global formability and cracking resistance of high strength DP steels can be balanced through microstructural tailoring.
Highlights
Dual Phase (DP) steels are one of the most extensively used Advanced High Strength Steels (AHSS) for body in white automobile components [1]. Their excellent compromise between high strength and good formability has contributed to their widespread implementation in passenger’s car, allowing vehicle weight reduction and enhancing oc cupant’s safety [1,2]. These steels belong to the first generation of AHSS family and are characterized by showing high strength, low yield strength to tensile strength (YS/TS) ratio, high strain hardening and high ductility compared to other high strength low-alloy steels [1,2,3]
Both DP steels are char acterized by a high initial strain hardening rate that rapidly decreases with increasing strain, which is typical from DP microstructures
Even though DP1000-B has higher initial n, it continuously decreases from the beginning of deformation
Summary
Dual Phase (DP) steels are one of the most extensively used Advanced High Strength Steels (AHSS) for body in white automobile components [1] Their excellent compromise between high strength and good formability has contributed to their widespread implementation in passenger’s car, allowing vehicle weight reduction and enhancing oc cupant’s safety [1,2]. These steels belong to the first generation of AHSS family and are characterized by showing high strength, low yield strength to tensile strength (YS/TS) ratio, high strain hardening and high ductility compared to other high strength low-alloy steels [1,2,3]. Their high strain hard ening is caused by the strain gradients between the soft matrix (ferrite)
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.
