Critical Assessment of Techniques for the Description of the Phase Composition of Advanced High-Strength Steels

Knaislová, Anna; Rudomilova, Darya; Novák, Pavel; Prošek, Tomáš; Michalcová, Alena; Béran, P.

doi:10.3390/ma12244033

Cited by 8 publications

(4 citation statements)

References 43 publications

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“…These findings are in good agreement with the assumptions derived from Figure 7 . For a cooling rate of 50 K/s, the amount of ferrite decreases in favor of bainite (B) and possibly tempered martensite, which is hardly distinguishable [ 47 ]. As expected from the transformation curves in Figure 7 , the micrographs of the carburized sheets in Figure 9 show martensitic structures for a nominal quenching rate of 70 K/s.…”

Section: Resultsmentioning

confidence: 99%

Investigation of the Microstructural Evolution during Hot Stamping of a Carburized Complex Phase Steel by Laser-Ultrasonics

Horn

Merklein

2021

Materials

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Prior carburization of semi-finished steel sheets is a new process variant in hot stamping to manufacture parts with tailored properties. Compared to conventional hot stamping processes, a complex phase typed steel alloy is used instead of 22MnB5. Yet recent investigations focused on final mechanical properties rather than microstructural mechanisms cause an increase in strength. Thus, the influence of additional carburization on the microstructural evolution during hot stamping of a complex phase steel CP-W®800 is investigated within this work. The phase transformation behavior, as well as the grain growth during austenitization, is evaluated by in-situ measurements employing a laser-ultrasound sensor. The results are correlated with additional hardness measurements in as-quenched condition and supplementary micrographs. The experiments reveal that the carburization process significantly improves the hardenability of the CP-W®800. However, even at quenching rates of 70 K/s no fully martensitic microstructure was achievable. Still, the resulting hardness of the carburized samples might exceed the fully martensitic hardness of 22MnB5 derived from literature. Furthermore, the carburization process has no adverse effect on the fine grain stability of the complex phase steel. This makes it more robust in terms of grain size than the conventional hot stamping steel 22MnB5.

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Section: Resultsmentioning

confidence: 99%

Investigation of the Microstructural Evolution during Hot Stamping of a Carburized Complex Phase Steel by Laser-Ultrasonics

Horn

Merklein

2021

Materials

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“…For each advanced steel, microstructural characterization was carried out by employing an Olympus PMG 3 optical microscope (Olympus Corporation of the Americas(OCA), Center Valley, PA, USA) and a JEOL JSC-6000 Plus Neoscope scanning electron microscope (JEOL Ltd., Tokyo, Japan). The microstructure of the CP steels was carried out using a chemical solution of LePera [28] by immersion for 2 min at room temperature. For the TWIP steels, it was revealed using Nital-10% [28] at 60 • C by immersion for 20 s. And for the Q&P steels, the microstructure was revealed by employing a modified solution of the LePera reactant [27] by immersion for 35 s at 70 • C.…”

Section: Treatment Of Advanced Steels Before Welding (Microstructure ...mentioning

confidence: 99%

“…The microstructure of the CP steels was carried out using a chemical solution of LePera [28] by immersion for 2 min at room temperature. For the TWIP steels, it was revealed using Nital-10% [28] at 60 • C by immersion for 20 s. And for the Q&P steels, the microstructure was revealed by employing a modified solution of the LePera reactant [27] by immersion for 35 s at 70 • C.…”

Section: Treatment Of Advanced Steels Before Welding (Microstructure ...mentioning

confidence: 99%

Microstructural Characterization and Corrosion Behavior of Similar and Dissimilar Welded Advanced High-Strength Steels (AHSS) by Rotary Friction Welding

Salas Reyes,

Lara Rodriguez,

González Parra

et al. 2024

Materials

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Advanced high-strength steels (AHSSs) are designed for meeting strict requirements, especially in the automotive industry, as a means to directly influence the reduction in the carbon footprint. As rotary friction welding (RFW) has many important advantages over other welding technologies, it plays an important role in the automotive sector. On the above basis, in this work, combinations of the first (complex phase (CP)), second (TWIP (TW)), and third (quenched and partitioned (Q&P)) generations of similar and dissimilar high-alloyed advanced steels have been joined by the RFW process. Having a specific microstructure, rods of CP/CP, Q&P/Q&P, CP/TW, and Q&P/TW steels were welded by employing a homemade adaptation machine under fixed parameters. Microstructural characterization has allowed us to corroborate the metallic bonding of all the tested advanced steels and to identify the different zones formed after welding. Results indicate that the welding zone widens in the center of the workpiece, and under the current friction action, the intermixing region shows the redistribution of solute elements, mostly in the dissimilarly welded steels. Furthermore, because of their complex chemistry and the different mechanical properties of the used steels, dissimilarly welded steels present the most noticeable differences in hardness. The TWIP steel has the lower hardness values, whilst the CP and Q&P steels have the higher ones. As a direct effect of the viscoplastic behavior of the steels established by the thermomechanical processing, interlayers and oxidation products were identified, as well as some typical RFW defects. The electrochemical response of the welded steels has shown that the compositional and microstructural condition mostly affect the corrosion trend. This means that the dissimilarly welded steels are more susceptible to corrosion, especially at the TWIP–steel interface, which is attributed to the energy that is stored in the distorted microstructure of each steel plate as a consequence of the thermomechanical processing during RFW.

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“…Complex-phase steel has a microstructure consisting of a ferrite/bainite matrix with small amounts of martensite, retained austenite and pearlite (Figure 12) [46].…”

Section: Complex Phase (Cp)mentioning

confidence: 99%

Ultra High Strength Steels for Roll Formed Automotive Body in White

Hardwicke

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One of the more recent steel developments is the quenching and partitioning process, first proposed by Speer et al. in 2003 on developing 3rd generation advanced highstrength steel (AHSS). The quenching and partitioning (Q&P) process set a new way of producing martensitic steels with enhanced austenite levels, realised through controlled thermal treatments. The main objective of the so-called 3rd generation steels was to realise comparable properties to the 2nd generation but without high alloying additions. Generally, Q&P steels have remained within lab-scale environments, with only a small number of Q&P steels produced industrially. Q&P steels are produced either by a one-step or two-step process, and the re-heating mechanism for the two-step adds additional complexities when heat treating the material industrially. The Q&P steels developed and tested throughout this thesis have been designed to achieve the desired microstructural evolution whilst fitting in with Tata's continuous annealing processing line (CAPL) capabilities. The CALPHAD approach using a combination of thermodynamics, kinetics, and phase transformation theory with software packages ThermoCalc and JMatPro has been successfully deployed to find novel Q&P steels. The research undertaken throughout this thesis has led to two novel Q&P steels, which can be produced on CAPL without making any infrastructure changes to the line. The two novel Q&P steels show an apparent reduction in hardness mismatch, illustrated visually and numerically after nanoindentation experiments. The properties realised after Q&P heat treatments on the C-Mn-Si alloy with 0.2 Wt.% C and the C-Mn-Si alloy with the small Cr addition is superior to the commercially available QP980/1180 steels by BaoSteel. Both novel alloys had comparable levels of elongation and hole expansion ratio to QP1180 but are substantially stronger with a > 320MPa increase in tensile stress. The heat treatment is also less complex as there is no requirement to heat the steel back up after quenching due to one-step quenching and partitioning being employed on the novel alloys.

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Critical Assessment of Techniques for the Description of the Phase Composition of Advanced High-Strength Steels

Cited by 8 publications

References 43 publications

Investigation of the Microstructural Evolution during Hot Stamping of a Carburized Complex Phase Steel by Laser-Ultrasonics

Investigation of the Microstructural Evolution during Hot Stamping of a Carburized Complex Phase Steel by Laser-Ultrasonics

Microstructural Characterization and Corrosion Behavior of Similar and Dissimilar Welded Advanced High-Strength Steels (AHSS) by Rotary Friction Welding

Ultra High Strength Steels for Roll Formed Automotive Body in White

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