Fatigue Crack Growth and Fracture Toughness in a Dual Phase Steel: Effect of Increasing Martensite Volume Fraction

Abstract

Crack growth resistance in dual-phase steel was studied. The dual phase steel microstructure was modified through heat treatments to increase the martensite volume fraction from 10% to 40%. The as-received and heat-treated samples were evaluated using a uniaxial tensile test, fatigue crack growth test, and fracture toughness test. Extended Finite Element Method (XFEM) was used to simulate the crack growth in compact tension test specimens. The results showed that an increase in martensite volume fraction is an effective way to increase the fracture resistance under different load conditions, quasistatics and dynamic, increasing the fracture toughness, tensile strength and fatigue resistance of the heat-treated material. Presence of a highest content of martensite results in formation of an important number of secondary cracks during the fatigue crack growth, which slow down the crack propagation. Moreover, martensite generates a crack closure over the crack tip, making the propagation difficult due to the irregularities caused by the crack growth on the martensite. Finally, the computational load-displacement curves are in good agreement with the experimental data.

Martensite content effect on fatigue crack growth and fracture energy in dual‐phase steels

“…Finally, ΔK th reported by Li et al shows an increasing trend with MVF increase, unlike the results presented in Table 2 where it remains constant, although its magnitude is in the range of values indicated by work of Li et al 23 Some authors report a behavior similar to that reported by Li et al, concerning the parameters C and m, 37 while others report opposite behaviors. For example, Idris et al in their work, obtained DP steels (25% wt of carbon) through intercritical heat treatments between 748 and 1000 C, with holding times of 90 minutes, 24 reporting a value of ΔK th =38 MPa.m 1/2 and m=3.94, for steel with 35% of MVF, while for steel with 45% of MVF, a value of ΔK th =35 MPa.m 1/2 and m=3.63.…”

“…The first set of results gathers the values reported by Bag et al 14,16 and the current investigation with an increasing tendency and magnitudes between 1.2 and 4.6. The second set gathers the results reported by Li et al, 23 Pérez et al, 37 and Dutta et al, 10 with an increasing trend and magnitudes between 3.6 and 5.8, with an outlier of 9.3. This parameter, the second most commonly reported in the literature, exhibits an increasing trend with the MVF.…”

Damage Evolution and Microstructural Fracture Mechanisms Related to Volume Fraction and Martensite Distribution on Dual‐Phase Steels

“…[ 23 ] Furthermore, the authors of the current study have previously documented that increasing the amount of martensite in the ferrite matrix increases the dual‐phase steel mechanical response under dynamic impact conditions [ 24 ] and fatigue. [ 25 ]…”

“…[23] Furthermore, the authors of the current study have previously documented that increasing the amount of martensite in the ferrite matrix increases the dual-phase steel mechanical response under dynamic impact conditions [24] and fatigue. [25] Due to the intercritical heat treatment temperature range used in the dual-phase steel production, the diffusion mechanism is less effective in transporting interstitial carbon atoms, so the resulting martensite produced during the quenching process has lower yield stress and hardness because of the lower and heterogeneous distribution of carbon content. [26] Moreover, recent research indicates that adding some alloying elements such as vanadium, increases martensite softening.…”

Fatigue crack propagation behavior of multiphase microstructure in a quenched and partitioned medium‐carbon bainitic steel

“…Li et al 17 investigated the FCP behavior in martensite-ferrite steel and pointed out that the roughness of fracture surface and secondary crack will be increased with increasing martensite content, leading to a lower FCP rate. Pérez-Vel asquez et al 18 reported that an increase in martensite content is an effective method to decrease the FCP rate of martensiteferrite steel due to the secondary crack and crack closure generated over the crack tips. Chen et al 19 studied the steel with bainite-martensite structure and suggested that the higher FCP resistance can be obtained when the bainite content is in the range of 49%-60%, which is ascribed to the coupled contributions from both crack deflection and plasticity-induced crack closure.…”