Fatigue performance of dual‐phase steels for automotive wheel application

Abstract

Fatigue performance of ferrite–martensite (FM) and ferrite–bainite (FB) dual‐phase (DP) steels used in automotive wheels has been compared in terms of (i) high‐cycle fatigue performance and failure mechanisms and (b) low‐cycle fatigue performance (Δεt/2 = 0.002 to 0.01) and associated deformation mechanisms. FBDP steel exhibits moderately better high‐cycle fatigue performance, owing to delay in microcrack initiation. In FBDP steel, microcracks initiate predominantly along ferrite grain boundaries, while that at FB interface is significantly delayed in comparison with FMDP steel, where few microcracks appear at FM interface even below the endurance limit. During low‐cycle fatigue, however, FMDP steel performs considerably better than FBDP steel till Δεt/2 ≤ 0.005 attributed to initial cyclic hardening, followed by cyclically stable behaviour exhibited by FMDP steel. In sharp contrast, at all Δεt/2 > 0.002, FBDP steel undergoes continuous cyclic softening. The latter may cause undesirable deformation of wheels in service.

Evaluation of the Low‐Cycle Fatigue Life of Thin Dual‐Phase Steel Sheets for Automobiles Using Miniature Specimens

“…1) Fatigue damage morphology. In the LCF regime, fatigue damage underRBF loading mainly occurred at the ferrite/martensite interfaces and inside ferrite grains (see Figure c), which is similar to the damage sites under TCF loading reported in the literature . In addition, the crack propagation path developed mainly along the ferrite/martensite interfaces under RBF loading is also similar to that under the TCF loading reported in the literature .…”

Relationships between Microstructural and Mechanical Performance on Example of an Air‐Hardening Steel

“…In contrast to this, the curve of the DP microstructure is more sloped, and for high cycle numbers, i.e., upwards of 10 6 cycles, the maximum stress amplitude is lower than that for the bimodal microstructure. This fatigue curve can be explained by a pronounced crack initiation, predominantly on the boundaries of hard martensite, with a microhardness of 240±8 HV0.01, and ductile ferrite phases, which have a microhardness of 173±17 HV0.01, even at lower stress levels (see Figure f) . Contrary to the DP material, the crack initiation in mono‐phase materials, both with normal and bimodal microstructures, seems to be delayed due to the more ductile nature of ferrite.…”

Effects of notch position on the fatigue crack growth behavior of dissimilar laser welded DP980/QP980 joint

“…Quenching and partitioning (QP) steel is one of the most attractive materials in AHSSs, because the retained austenite (RA) transforms into martensite during the deformation process, resulting in high tensile strength and ductility 1 . Due to the advantages of high strength, high plasticity, continuous yield, and high initial work hardening rate, dual‐phase (DP) steel was also widely used in the automotive industry 2,3 . Tailor‐welded QP and DP steel can meet the needs of different parts of automobiles and has important application prospects in improving the lightweight and safety of automobiles.…”