Liquid-Metal-Induced Embrittlement of Zn-Coated Hot Stamping Steel

Lee, Chang-Wook; Fan, Dong; Sohn, Il Ryoung; Lee, Seok-Jae; Cooman, Bruno C. De

doi:10.1007/s11661-012-1316-0

Cited by 108 publications

(51 citation statements)

References 14 publications

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“…8,20) In the present study, the die-quenched Zn coating on the PHS was composed of Γ-Fe3Zn10 and α-Fe(Zn). The Zn concentration of Γ-Fe3Zn10 and α-Fe(Zn) phases was about 80 wt.% and 30 wt.%, respectively.…”

Section: Discussionmentioning

confidence: 84%

“…The effect of the soaking time and the coating thickness or weight on LMIE and microcrack propagation has been reported previously and the reduction of the susceptibility to LMIE and microcrack propagation with increased soaking times or reduced coating weights has also been reported. 8,[32][33][34][35] It is expected that a reduction of the applied stress during press hardening process should also be beneficial. The area most vulnerable to LMIE microcrack formation is the outer wall.…”

Section: Discussionmentioning

confidence: 99%

“…The elongations is also considerable, typically 40% at the forming temperature. 8,9) During the die-quenching in the direct press hardening process method the sheets are heated and simultaneously formed and die-quenched. The material is heated above the A3 temperature to the austenite stability range and the forming and quenching carried out in water-cooled dies.…”

Section: Introductionmentioning

confidence: 99%

“…14,15) However, the formation of small surface cracks on die-quenched Zn-coated PHS panels related to liquid metal induced embrittlement (LMIE), has been widely reported. 8) Because of the low melting temperature of Zn and Fe-Zn intermetal-© 2015 ISIJ lic compounds, most of the Zn and Zn-alloy coatings are partially liquid at the austenitizing temperature. If sufficient stress is applied during the forming operation at high temperature, a Fe-saturated liquid Zn, appears to penetrate into the austenite grain boundaries causing an embrittlement characterized by surface crack formation due to a rapid intergranular fracture.…”

Section: Introductionmentioning

confidence: 99%

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Liquid-Metal-Induced Embrittlement Related Microcrack Propagation on Zn-coated Press Hardening Steel

et al. 2015

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The coatings on press hardening steel are needed to suppress high temperature oxidation and decarburization. Additional corrosion protection is provided by Zn coatings which provide cathodic protection to press hardened parts. Due to the low melting temperature of Zn and Zn-Fe intermetallic compounds, the Zn-coated PHSs are susceptible to LMIE during the die-quenching process. In the present work, the mechanical properties of Zn coated PHS were evaluated in terms of tensile properties and bending properties. A deterioration of the room temperature bendability, due to microcrack formation and propagation, was observed. The presence of Γ-Fe3Zn10 observed in the microcracks at room temperature correspond to liquid Zn at the die-quenching temperature, making it possible to trace the progress of the liquid Zn phase during microcrack formation. The results suggest that Zn-grain boundary diffusion causes the phase transformation to ferrite of the austenite grain boundary region. This results in intergranular cracking due to the lower strength of ferrite. The LMIE microcrack formation is most severe in areas where the applied stress and the friction are highest during the forming process, making the occurrence of LMIE-mitigated microcrack propagation dependent on the local deformation conditions.

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Section: Discussionmentioning

confidence: 84%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Liquid-Metal-Induced Embrittlement Related Microcrack Propagation on Zn-coated Press Hardening Steel

et al. 2015

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“…by extension of the blank soaking time to protect the steel from LMIE. 17) Micro-cracks occur mainly in the part of the blank exposed to high friction during die quenching. The micro-crack formation can be suppressed by the use of © 2014 ISIJ a lubricant to reduce the coating/die friction.…”

Section: Introductionmentioning

confidence: 99%

Surface Oxide Formation during Rapid Heating of Zn-coated Press Hardening Steel

et al. 2014

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During the conventional die-quenching processing of a galvanized PHS steel, a thick ZnO layer is formed at the surface. When the heating rate is increased, the oxide at the surface is a thin Al2O3 layer. This remarkable change in surface oxide during rapid heating is due to the partial melting of the coating instead of the solidification of the coating and the formation of Fe-Zn intermetallics. In the present study, the characterization of the surface oxide formation at different heating rates is presented.

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Complementary in‐situ electrochemical ICP‐OES and corrosion studies of hot‐formed zinc alloy coated steel

Wiesener

Schinkinger

Grundmeier

2015

Materials & Corrosion

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A spectroelectrochemical approach for the fundamental analysis of the cathodic corrosion behavior of hot‐formed zinc alloy coated steel based on the in‐situ combination of inductively coupled plasma‐optical emission spectroscopy (ICP‐OES) is presented. Complementary to the microscopic information on the alloy dissolution, line‐scans of the free corrosion potential were measured across welding spots with a scanning capillary cell (SCC) to illustrate both the change in the local coating integrity and the ability of the coating to cathodically protect possible defects in the welding spot area. These studies were performed as a function of the holding time during hot‐forming. The results of the coulometric ICP‐OES measurements and the potential line‐scans are in very good agreement and show that in‐situ ICP‐OES provides insight into the dissolution behavior of zinc alloys that goes far beyond standard electrochemical techniques such as coulometry alone. It could be shown that the hot‐forming induced alloying of zinc with iron leads to preferential dissolution of zinc in the initial phase and to a parallel dissolution of iron and zinc in the second phase. For zinc‐nickel alloys the initial preferential zinc dissolution leads to a fast de‐alloying and the dissolution of the nickel rich phase occurs at rather anodic potentials. The alloying of nickel into zinc coatings leads to an inhibition of the zinc dissolution and hence to a decrease of the cathodic corrosion protection ability. However, the zinc‐nickel coatings are more resistant to evaporation and the defect formation in the welding spot is less significant. It could be shown that under the same conditions an aluminum silicon alloy does not show a significant preferential anodic dissolution hinting at a negligible cathodic protection.

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Liquid-Metal-Induced Embrittlement of Zn-Coated Hot Stamping Steel

Cited by 108 publications

References 14 publications

Liquid-Metal-Induced Embrittlement Related Microcrack Propagation on Zn-coated Press Hardening Steel

Liquid-Metal-Induced Embrittlement Related Microcrack Propagation on Zn-coated Press Hardening Steel

Surface Oxide Formation during Rapid Heating of Zn-coated Press Hardening Steel

Complementary in‐situ electrochemical ICP‐OES and corrosion studies of hot‐formed zinc alloy coated steel

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