Strain-rate sensitive ductility in a low-alloy carbon steel after quenching and partitioning treatment

Frint, Philipp; Kaiser, Till; Mehner, Thomas; Bruder, Enrico; Scholze, Mario; Mašek, Bohuslav; Lampke, Thomas; Wagner, Martin F.‐X.

doi:10.1038/s41598-019-53303-1

Cited by 11 publications

(6 citation statements)

References 29 publications

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“…[ 13 ] This is in line with the results obtained for the QP220 condition in the present study and is further underlined by the strain hardening rate versus true strain curves (plotted up to the onset of necking, i.e., the point where the strain hardening rate becomes equal to the true tensile stress [ 45 ] ) of the two investigated conditions shown in Figure 5b. Generally, both conditions are characterized by high strain hardening rates being in line with the results reported by Frint et al [ 46 ] for Q&P‐processed materials. Besides the carbon content, the stability of the RA is also affected by its morphology.…”

Section: Resultssupporting

confidence: 91%

Experimental Analysis of the Stability of Retained Austenite in a Low‐Alloy 42CrSi Steel after Different Quenching and Partitioning Heat Treatments

et al. 2023

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Quenching and partitioning (Q&P) steels are characterized by an excellent combination of strength and ductility, opening up great potentials for advanced lightweight components. The Q&P treatment results in microstructures with a martensitic matrix being responsible for increased strength whereas interstitially enriched metastable retained austenite (RA) contributes to excellent ductility. Herein, a comprehensive experimental characterization of microstructure evolution and austenite stability is carried out on a 42CrSi steel being subjected to different Q&P treatments. The microstructure of both conditions is characterized by scanning electron microscopy as well as X‐ray diffraction (XRD) phase analysis. Besides macroscopic standard tensile tests, RA evolution under tensile loading is investigated by in situ XRD using synchrotron and laboratory methods. As a result of different quenching temperatures, the two conditions considered are characterized by different RA contents and morphologies, resulting in different strain hardening behaviors as well as strength and ductility values under tensile loading. In situ synchrotron measurements show differences in the transformation kinetics being rationalized by the different morphologies of the RA. Eventually, the evolution of the phase specific stresses can be explained by the well‐known Masing model.

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Section: Resultssupporting

confidence: 91%

Experimental Analysis of the Stability of Retained Austenite in a Low‐Alloy 42CrSi Steel after Different Quenching and Partitioning Heat Treatments

et al. 2023

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“…For a Q&P steel, Frint et al suggested that strain rate sensitive ductility was more pronounced at 200°C than at room temperature. [98] In addition to dislocation slip, dislocation recovery, and DIMT, interface plasticity was proposed as a relevant mechanism at elevated temperatures. Recently, a greater understanding of interface plasticity in AHSS microstructures has been reached, [99,100] but has not yet been satisfactorily applied in formability studies.…”

Section: B Mechanical Performance and Dimt In Trip-assisted Ahssmentioning

confidence: 99%

Strain Rate Dependent Ductility and Strain Hardening in Q&P Steels

Finfrock

Thrun

Bhattacharya

et al. 2021

Metall Mater Trans A

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Due to their high strength, formability and affordable cost, quenched and partitioned (Q&P) steels have shown the potential to reduce the mass of vehicles, thereby decreasing fuel consumption during service. Furthermore, because a lower mass of steel is used in each vehicle, energy consumption associated with the steelmaking process is also reduced. Q&P steels utilize the deformation-induced martensitic transformation (DIMT) of metastable retained austenite to enhance ductility and strain hardening. Accordingly, improvement of mechanical performance is contingent on the ability to precisely control the chemical and mechanical stability of austenite. Considering the multitude of factors that influence austenite stability, optimizing microstructures to delay necking or fracture is challenging, particularly as temperature and strain rate increase. Tensile tests of an intercritically annealed C-Mn-Si Q&P steel were performed over a range of strain rates (10 À4 to 10 À1 s À1 ) to evaluate effects on the DIMT and sheet tensile properties. As strain rates increased from 10 À4 to 10 À1 s À1 , the uniform elongation decreased from approximately 19 to 14 pct. This reduction in uniform elongation is associated with a decrease in the strain hardening exponent near the onset of strain localization. Based on experimental data from this study and review of previous research, it is postulated that the strengthening contribution of DIMT is controlled by competing effects of: (i) a decreasing chemical driving force for DIMT caused by deformation-induced heat accumulation at higher strain rates and (ii) an increasing number of martensite nucleation sites. This suggests that tailoring austenite stability for specific deformation conditions could enable further optimization of formability and vehicle crash behavior.

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“…In a recent in situ study [15], Liehr et al presented the stress-induced evolution of retained austenite fractions with different morphologies in a low-alloy steel as a function of strain. Frint et al [16] additionally observed exceptionally high ductility during forming at temperatures around 200 °C after Q&P heat treatment. Their results suggest a diffusion-controlled deformation mechanism at elevated temperatures.…”

Section: Introductionmentioning

confidence: 95%

Experimental and Numerical Process Design for Press Partitioning of the New Q&P Steel 37SiB6

Illgen,

Winter,

Haase

et al. 2023

Metals

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Quenching and partitioning (Q&P) heat treatments of low-alloy steels with exceptional property combinations are particularly promising. In this study, we characterize for the first time a new low-alloy steel to be processed using Q&P heat treatments. In combined experimental and numerical studies, we design a novel approach that effectively combines the short cycle times of press hardening with the excellent property profiles of Q&P-treated steels. We identify an appropriate austenization temperature of 950 °C and a portioning temperature of 250 °C for Q&P heat treatments through dilatometric studies. We adjust a number of reference conditions with fractions of 2.1 to 6.3 wt.% of retained austenite, resulting in tensile strengths up to 1860 MPa and elongations to failure up to 7%. Initial numerical designs of the process can identify varying temperature profiles and cooling rates depending on the position in the die. The results show that the geometry of the part plays a minor role, but the die temperature of 200 °C is the dominant factor for successful partitioning directly in the press hardening process.

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Strain-rate sensitive ductility in a low-alloy carbon steel after quenching and partitioning treatment

Cited by 11 publications

References 29 publications

Experimental Analysis of the Stability of Retained Austenite in a Low‐Alloy 42CrSi Steel after Different Quenching and Partitioning Heat Treatments

Experimental Analysis of the Stability of Retained Austenite in a Low‐Alloy 42CrSi Steel after Different Quenching and Partitioning Heat Treatments

Strain Rate Dependent Ductility and Strain Hardening in Q&P Steels

Experimental and Numerical Process Design for Press Partitioning of the New Q&P Steel 37SiB6

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