“…Therefore, in order to guarantee safety of forming parts, current density of 10.0 A mm −2 is an appropriate value for forming HSS due to a good performance of energy absorption. 21 10 Room temperature tensile curves of forming parts with forming at various current density…”
Section: Resultsmentioning
confidence: 99%
“…Therefore, in order to guarantee safety of forming parts, current density of 10.0 A mm −2 is an appropriate value for forming HSS due to a good performance of energy absorption. 21 According to the rule that properties of alloy are determined by microstructure itself, the observing location and the corresponding microstructure are shown in Fig. 11.…”
Section: Quality Analysis Of the Hot-stamping Parts And Microstructur...mentioning
This paper investigated the influence of electric pulses on the microstructure evolution and mechanical property of hot-stamping process of DP1180. The thickness distribution and absorbed energy of the forming parts were also calculated. The results showed that dynamic recrystallisation occurs in the middle zone in the current auxiliary tension. Moreover, the current would bypass the microcrack. The current auxiliary hot-stamping can be carried out with a current density of 9.7-10.4 A mm −2 , thickness distribution formed at 10.4 A mm −2 has the lowest fluctuation of thickness with thinnest rate of 18.7% in middle. The tensile-strength decreased with increasing the current density from 9.7 to 10.4 A mm −2 while elongation increased and the absorbed energy can reached 28.39 kJ at current density of 10.0 A mm −2 .
“…Therefore, in order to guarantee safety of forming parts, current density of 10.0 A mm −2 is an appropriate value for forming HSS due to a good performance of energy absorption. 21 10 Room temperature tensile curves of forming parts with forming at various current density…”
Section: Resultsmentioning
confidence: 99%
“…Therefore, in order to guarantee safety of forming parts, current density of 10.0 A mm −2 is an appropriate value for forming HSS due to a good performance of energy absorption. 21 According to the rule that properties of alloy are determined by microstructure itself, the observing location and the corresponding microstructure are shown in Fig. 11.…”
Section: Quality Analysis Of the Hot-stamping Parts And Microstructur...mentioning
This paper investigated the influence of electric pulses on the microstructure evolution and mechanical property of hot-stamping process of DP1180. The thickness distribution and absorbed energy of the forming parts were also calculated. The results showed that dynamic recrystallisation occurs in the middle zone in the current auxiliary tension. Moreover, the current would bypass the microcrack. The current auxiliary hot-stamping can be carried out with a current density of 9.7-10.4 A mm −2 , thickness distribution formed at 10.4 A mm −2 has the lowest fluctuation of thickness with thinnest rate of 18.7% in middle. The tensile-strength decreased with increasing the current density from 9.7 to 10.4 A mm −2 while elongation increased and the absorbed energy can reached 28.39 kJ at current density of 10.0 A mm −2 .
“…X‐Ray diffraction (XRD) analysis was performed by a scan step of 0.02° and a counting time of 1.5 s. In order to eliminate the possible machining effects and obtain a underformed measurement surface, all samples were mechanically polished in colloidal silica and chemically etched with a 2% nital solution before XRD tests. [ 9,31 ] The integrated intensities of (200) α , (211) α , (220) α peaks of ferrite and (200) γ , (220) γ , (311) γ peaks of austenite were used to quantitatively analyze the volume fraction of retained austenite ( V γ ) of undeformed and fatigue‐failed states at different total strain amplitudes applied. [ 32 ] The carbon content in retained austenite ( C γ ) was estimated according to the equation in the literature.…”
Carbide-free bainitic steels have an extensive application in the railway and automotive industries because of excellent mechanical properties, such as strength, ductility, and toughness. [1][2][3][4][5][6][7] Based on the outstanding properties of this class of steel, some traditional dual-phase (DP) and conventional transformationinduced plasticity (TRIP) steels are expected to be replaced. [7][8][9] The typical microstructure of these steels is mainly composed of fine bainitic ferrite containing high density of dislocations, metastable retained austenite, and/or hard martensite. [1][2][3][4][5][6][7] The high strength is attributed to the fine scale of bainitic ferrite, high density of dislocations, and/or hard martensite; and the TRIP effect caused by the transformation of austenite to martensite induced by monotonic tensile strain provides the possibility for simultaneously strengthening and toughening of carbidefree bainitic steels. [10][11][12] So far, many investigations focus on the effect of the content and stability of retained austenite on mechanical properties of carbide-free bainitic steels. However, the tensile properties and corresponding monotonic deformation behaviors closely associated with the microstructural evolution of carbidefree bainitic steels are rarely reported.In practical applications, most of structural components in railway and automotive fields, such as rails/crossings, chassis, axles and suspension arms, and so on, are usually damaged or fatigue-failed owing to tension-compression cyclic deformation with large strains. [13][14][15][16][17][18] Therefore, understanding the low-cycle fatigue (LCF) properties and their influencing factors of structural components are very important for investigating the safe service condition. According to previous publications, austenite-to-martensite transformation can occur at accumulated plastic strain during cyclic loading, thereby influencing the cyclic deformation behavior and fatigue life. [15][16][17][18] As reported, the martensitic transformation from austenite induced by strain helps to promote cyclic hardening due to the TRIP effect, but shorten the fatigue life because of the existence of freshly brittle martensite, especially for austenitic stainless steels with larger amounts of retained austenite; [19][20][21] in the literature, however, it has been reported that the martensitic transformation from austenite in austenitic stainless steels with more retained austenite can not only promote cyclic hardening, but also contribute to increasing the fatigue life due to the TRIP effect. [22][23][24] Differently, several authors suggested that the transformation of austenite to martensite is not the main influencing factor of cyclic hardening for traditional DP and conventional TRIP steels with less amount of retained austenite, while it is beneficial to increase the fatigue life of these steels due to the TRIP effect. [25][26][27] In addition, these above reports also suggested that cyclic softening resulted from dislocation rearrangement a...
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