13-14 June 2022
Schönbrunn Palace/Apothekertrakt
Europe/Vienna timezone

PHS Materials and Coatings – Robustness in Complexity combined with Tailoring in Perfection

13 Jun 2022, 13:00
1h
Schönbrunn Palace/Apothekertrakt

Schönbrunn Palace/Apothekertrakt

Apothekertrakt Schönbrunn, Meidlinger Tor, Grünbergstraße, 1130 Vienna

Speaker

Josef Faderl (voestalpine Stahl GmbH)

Description

The high volume application of PHS material in state of the art Body-in-White concepts is driven by high variety of possibilities to adapt the properties of PHS parts perfectly to the needs. This is true not only in respect to the strength (500 up to 2000 MPa) - even locally - crash-performance and high weight reduction target, but also regarding surface properties. PHS part production controls final coating- and base materials formation and properties. The intermetallic coating formation due to press hardening is very complex on the one hand, but surprisingly robust on the other hand. Thus reasonable process windows are provided. New developments are targeting to extend application possibilities as well as to increase cost-effectiveness.
One example of unexpected robustness was outlined in the awarded paper. The risk of so-called 2’nd order micro cracking during part production of galvanized PHS parts at hot forming temperatures less than 750°C is very limited. The depth of the micro cracks does not exceed a few multiples of 10 µm due the micro crack formation mechanism resp. available amount of Zn atoms generated by cracking of the solidified ZnFe-coating in an oxygen depleted surrounding atmosphere. Micro cracking of galvanized PHS was the most discussed topic in session 3.
One paper was focusing on modifications of the AlSi coating composition by adding Mg and Zn to improve specific coating and surface properties like corrosion creepage and/or paint appearance. A further topic was the formation of the surface oxide on press hardened galvanized steel sheets including the effect of shot blasting. Avoiding of surface conditioning, like slight shot blasting, for galvanized PHS parts by specific in-line surface treatments is a very challenging but also very beneficial development goal. Another topic of interest is the modification of surface emissivity to increase heating rates in the furnace and/or to compensate different heating rates, as a consequence of different sheet thicknesses (TWB, TRB). This can be achieved by using GI or GA for galvanized coatings or also by darkening of the coating surface by in-line or off-line surface treatments as shown in one paper. For a very high strength level, hydrogen embrittlement is also an important issue as shown by the paper from VW in the automotive session. Reduction of coating thickness is in consideration for several reasons like improvement of bending resp. crash properties, especially for very high strength PHS material (> 1800 MPa). Surface decarbonisation treatment, is a further approach to increase bendability. Improvement of productivity of part production by development of countermeasures to minimize coating build up on PHS furnace rolls, preferable in cooperation with equipment suppliers, is a hot topic too.
To sum up there are enough questions to be answered, mechanism to be well-understood and other future development issues in respect to PHS coatings. Let us go for them.

Best Paper Winner Josef Faderl , voestalpine Stahl GmbH, will present highlights from his Galvatech 2021 paper "Avoiding Zinc Induced Cracking In Hot Forming". Highlights from other Galvatech 2021 papers on zinc-coated press hardened steel advances will also be summarized.

Each session will start with the 20 minute lecture, followed by a 20 minute panel discussion. This will be followed by 10 minutes of general discussion and a short break before beginning the next session.

Keywords

galvanizing, press hardening, PHS, hot forming, micro cracks, liquid metal embrittlement, LME, vapour metal embrittlement , VME

Primary author

Josef Faderl (voestalpine Stahl GmbH)

Co-authors

Dr Johannes Haslmayr (HTL Paul-Hahn-Straße 4) Mr Sigi Kolnberger (voestalpine Stahl GmbH) Mr Thomas Kurz (voestalpine Stahl GmbH)

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