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Liquid Metal Embrittlement during Hot Forming of Hot-Dip Galvanized Advanced High-Strength Unalloyed Steels (AHSS)

  • R. Haubner and S. Strobl
Published/Copyright: August 2, 2019
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Practical Metallography
From the journal Practical Metallography Volume 56 Issue 8

Abstract

Advanced High-Strength Steels (AHSS) are of interest as, owing to their increased strength, they are able to absorb more energy than conventional steels in a car crash. Thus, thinner metal sheets can be used for car design so that vehicle weight and fuel consumption are reduced. The elements Si, Mn, Al, and B are added in order to achieve the desired AHSS alloy properties. Corrosion protection for the automotive sheet metal is mainly ensured by hot-dip galvanizing. The sheets are further processed by hot forming.

Hot-dip galvanized steel sheets made of 20MnB8 were examined after high temperature tensile tests. Metallographic examinations were performed on tensile test specimens which were tested at temperatures between 400 and 800 °C and strain rates between 0.05 and 5 s−1.

Liquid metal embrittlement was observed at temperatures above 700 °C. Lower strain rates resulted in a smaller degree of liquid metal embrittlement.

In order to avoid the occurrence of liquid metal embrittlement during hot forming of galvanized AHSS sheets, the relevant process parameters need to be further optimized.

Kurzfassung

Advanced High-Strength Steels (AHSS) sind interessant, weil diese durch ihre erhöhte Festigkeit beim Zusammenstoß zweier Autos mehr Energie absorbieren können als konventionelle Stähle. Dies ermöglicht die Verwendung dünnerer Bleche bei der Autokonstruktion, wodurch das Fahrzeuggewicht reduziert wird und auch der Treibstoffverbrauch sinkt. Um die gewünschten Eigenschaften der AHSS Legierungen zu erreichen, werden Si, Mn, Al und B zulegiert. Für den Korrosionsschutz werden Automobilbleche überwiegend feuerverzinkt. Die Weiterverarbeitung der Bleche erfolgt danach mittels Warmverformung.

Es wurden feuerverzinkte Stahlbleche der Qualität 20MnB8 nach Hochtemperaturzugversuchen untersucht. Metallographische Untersuchungen wurden an Zugversuchsproben durchgeführt, die bei Temperaturen zwischen 400 und 800 °C, mit Dehnraten zwischen 0,05 und 5 s−1 geprüft wurden.

Bei Temperaturen über 700 °C wurde Lotbruch beobachtet. Das Ausmaß des Lotbruchs war bei kleineren Dehnraten geringer.

Um verzinkte AHSS Bleche durch Warmumformung bearbeiten zu können, ohne dass Lotbruch auftritt, ist eine weitere Optimierung der Prozessparameter bei der Warmverformung notwendig.

Translation: E. Engert

References / Literatur

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Received: 2019-02-12
Accepted: 2019-02-18
Published Online: 2019-08-02
Published in Print: 2019-08-14

© 2019, Carl Hanser Verlag, München

Articles in the same Issue

  1. Contents/Inhalt
  2. Contents
  3. Editorial
  4. Editorial
  5. Technical Contributions/Fachbeiträge
  6. Etchant for Normal and Abnormal Grain Growth Microstructure in RAFM Steel at Different Annealed Temperatures
  7. The Effect of TiO2 Nanoparticle Adding on Inclusion and Microstructure
  8. Microstructure and Magnetic Properties of Polymer Bonded Magnets produced by Additive Manufacturing Technologies
  9. Liquid Metal Embrittlement during Hot Forming of Hot-Dip Galvanized Advanced High-Strength Unalloyed Steels (AHSS)
  10. Meeting Diary/Veranstaltungskalender
  11. Meeting Diary
https://doi.org/10.3139/147.110590

Articles in the same Issue

  1. Contents/Inhalt
  2. Contents
  3. Editorial
  4. Editorial
  5. Technical Contributions/Fachbeiträge
  6. Etchant for Normal and Abnormal Grain Growth Microstructure in RAFM Steel at Different Annealed Temperatures
  7. The Effect of TiO2 Nanoparticle Adding on Inclusion and Microstructure
  8. Microstructure and Magnetic Properties of Polymer Bonded Magnets produced by Additive Manufacturing Technologies
  9. Liquid Metal Embrittlement during Hot Forming of Hot-Dip Galvanized Advanced High-Strength Unalloyed Steels (AHSS)
  10. Meeting Diary/Veranstaltungskalender
  11. Meeting Diary
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