Effect of Cooling Path on Microstructures and Hardness of Hot-Stamped Steel

Xu, Yanguang; Ji, Qiumei; Yang, Gengwei; Bao, Siqian; Zhao, Gang; Miao, Xiaodong; Mao, Xinping

doi:10.3390/met10121692

Cited by 4 publications

(4 citation statements)

References 45 publications

(67 reference statements)

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“…Martensitic steel 22MnB5 was chosen as the experimental material. This material is a typical representative of press-hardened steels, which combines good formability with high strength [19][20][21][22][23][24]. In the automotive industry, these unique material properties are used to reduce BIW while maintaining good crash resistance [25].…”

Section: Methodsmentioning

confidence: 99%

Determining Forming Limit Diagrams Using Sub-Sized Specimen Geometry and Comparing FLD Evaluation Methods

Rubešová

Rund

Rzepa

et al. 2021

Metals

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Sheet metal forming boundaries are established using the forming limit diagram (FLD). The Nakajima and Marciniak tests, which are based on stretching a material using a punch, are the most commonly used methods for determining the FLD or fracture forming limit diagram (FFLD). The results are usually evaluated by calculating local strain, strain rates, specimen thickness reduction or fracture strain. When the amount of experimental material is insufficient, miniaturization of the testing specimens may be a solution. However, the interchangeability of the results for standard and miniaturized specimens has not been proven yet. In this study, the Nakajima tests were performed using standard and sub-sized specimens made of manganese–boron steel 22MnB5, commonly used in the automotive industry. Afterwards, four FLD/FFLD evaluation methods were applied and compared. The miniaturized specimens yielded higher strain values, which was explained by the varied ratio of material thickness/punch diameter and different bending conditions. The highest compliance of the results was recorded for the standard and miniaturized FFLD.

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Section: Methodsmentioning

confidence: 99%

Determining Forming Limit Diagrams Using Sub-Sized Specimen Geometry and Comparing FLD Evaluation Methods

Rubešová

Rund

Rzepa

et al. 2021

Metals

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show abstract

“…In Figure 14 are shown the microstructures of two radius samples, 11 and 14, acquired from outer, central and inner regions of the corner. Cold bending has shown to impact the through-thickness microstructure of steels, due to the tensile strain state in outer regions, compressive strain state in inner regions and neutral state in the center, and such behavior has been thoroughly depicted in the literature [48][49][50][51] . On the other hand, studies focused on the microstructural evolution during hot or warm sheet bending are scarce.…”

Section: Microstructure As Affected By the Hot Stamping Processmentioning

confidence: 99%

“…As shown by Lu et al 13 , tempered martensite is morphologically defined by poorly-defined boundaries and a relatively coarse structure as compared with quenched martensite, in addition to the presence of carbides that precipitate as a result of carbon rejection, which can be easily seen in the form of fine white particles. Xu et al 51 associate these particles with carbides. Rezayat et al 34 and Tamizi et al 65 reported that tempering at higher temperatures leads to the formation of coarser carbides, especially in the form of films along the boundaries of martensitic substructures, while tempering at lower temperatures results in the precipitation of finer and more dispersed particles.…”

Section: Rsw Martensite Tempering Simulationmentioning

confidence: 99%

Microstructural Evolution of a Hot-Stamped Boron Steel Automotive Part and Its Influence on Corrosion Properties and Tempering Behavior

et al. 2023

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Boron-manganese steel 22MnB5 is extensively used in structural automotive components. Knowledge about its microstructural evolution during hot stamping and resistance spot welding (RSW) is extremely relevant to guarantee compliance with application requirements. Particularly, corrosion properties are critical to the application of uncoated sheet steels. However, microstructural studies are usually simplified to top-hat geometries, which might not be fully representative of the complex thermomechanical cycles locally faced by a real component. Therefore, the present work brings an extensive characterization of a hot-stamped 22MnB5 automotive B-pillar in terms of microstructure, hardness and corrosion resistance, which were correlated with a reverse engineering of the process using numerical simulation. Physical simulations of the subcritical heat affected zone (SCHAZ) of RSW were done to assess the influence of microstructure on martensite tempering. Results showed that the component undergoes a complex strain distribution along its body during hot stamping. Most heavily strained regions presented higher amounts of ferrite, leading to poorer corrosion resistance, since ferrite behaves as an anode. Physical simulations of the SCHAZ showed that the softening degree due to martensite tempering is solely affected by peak temperature, while other microstructural features appear to exert negligible or no influence.

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“…This is a consequence of the shifting of the CCT (continuous cooling transformation) curves at higher transformation times. This shift is observed by comparing the CCT curves of 22MnB5 obtained in [16][17][18] and the CCT curves of 37MnB5 described in the work of [18].…”

Section: Physical Simulation Of Thermo-mechanical Press-hardening Cyclesmentioning

confidence: 99%

Study of Tailored Hot Stamping Process on Advanced High-Strength Steels

Palmieri

Galetta

Tricarico

2022

JMMP

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Ultra-high-strength steels (UHSS) combined with tailor-stamping technologies are increasingly being adopted in automotive body production due to crashworthiness improvements and part weight reduction, which meet safety and energy saving demands. Recently, USIBOR®2000 (37MnB5) steel has been added to the family of UHSS. This new material allows higher performance with respect to its predecessor USIBOR®1500 (22MnB5). In this work, the two steels are compared for the manufacturing of an automotive B-Pillar by press-hardening with a tailored tool tempering approach. A Finite Element (FE) model has been developed for the numerical simulation of thermomechanical cycles of the press-hardening process. The FE-simulations have been performed with the aim of obtaining soft zones in the part, by varying the quenching time and the temperature of heated tools. The effects of these parameters on the mechanical properties of the part have been experimentally evaluated thanks to hardness and tensile tests performed on specimens subjected to the numerical thermo-mechanical cycles using the Geeble-3180 physical simulator. The results show that for both UHSS, an increase in quenching time leads to a decrease in hardness up to a threshold value, which is lower for the USIBOR®1500. Moreover, higher mechanical resistance and lower elongation at break values are derived for the USIBOR®2000 steel than for USIBOR®1500 steel.

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Effect of Cooling Path on Microstructures and Hardness of Hot-Stamped Steel

Cited by 4 publications

References 45 publications

Determining Forming Limit Diagrams Using Sub-Sized Specimen Geometry and Comparing FLD Evaluation Methods

Determining Forming Limit Diagrams Using Sub-Sized Specimen Geometry and Comparing FLD Evaluation Methods

Microstructural Evolution of a Hot-Stamped Boron Steel Automotive Part and Its Influence on Corrosion Properties and Tempering Behavior

Study of Tailored Hot Stamping Process on Advanced High-Strength Steels

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