Suppression of Coating Layer Crack by Diffusion Heat Treatment in Al-Si Coated HPF Steels

Raman Spectroscopic Analysis of the Reaction between Al-Si Coatings and Steel

“…4,45 Other compounds that have been identified as minority components after the hot-dipping process include τ 1 , τ 6 , η, and θ. 8,17,25,46 Previous studies have reported that θ and η form at ca. 650 °C, 14 τ 2 at 830 °C, 8 AlFe at 882 °C, 20 and τ 1 at 900 °C.…”

“…15,20 Some EDS and electron back-scattering diffraction measurements suggest that Al-Si-coated steels heated to 900 °C contain mixtures of τ 1 , τ 2 , and ω (FeSi 2 ), 24 while others show τ 1 , τ 5 , AlFe, Al 2 Fe, θ, and η. 15,18,20,25,46 Variations in the composition of the Al-Si-Fe layer may arise due to variations in heating time. The temperatures at which Raman spectra identify new phases here are consistent with these observations, attesting to the accuracy of the Raman spectroscopy-based assignment.…”

“…In the case of the as-received steel, for example, the dip-coating process is known to produce a layer of τ 5 at the steel interface. ,,,, This layer acts as a barrier between the Al-Si coating and the Fe in the substrate steel, thereby inhibiting further transformation of the Al-Si coating up to 580 °C. , Other compounds that have been identified as minority components after the hot-dipping process include τ 1 , τ 6 , η, and θ. ,,, Previous studies have reported that θ and η form at ca. 650 °C, τ 2 at 830 °C, AlFe at 882 °C, and τ 1 at 900 °C. , AlFe and Al 2 Fe 2 Si emerge at higher temperatures, around 900 °C. , Some EDS and electron back-scattering diffraction measurements suggest that Al-Si-coated steels heated to 900 °C contain mixtures of τ 1 , τ 2 , and ω (FeSi 2 ), while others show τ 1 , τ 5 , AlFe, Al 2 Fe, θ, and η. ,,,, Variations in the composition of the Al-Si-Fe layer may arise due to variations in heating time. The temperatures at which Raman spectra identify new phases here are consistent with these observations, attesting to the accuracy of the Raman spectroscopy-based assignment.…”

Overcoming the strength–formability trade-off in high strength steels via cryogenic treatment

“…Although there are several variants of light materials such as Al and Mg alloys that can be used for structural components in automobiles, the characteristics of AHSS such as their high strength and low manufacturing cost make them materials of choice over other materials 3 – 5 . Among several grades of AHSS, hot press forming (HPF) steels, also called press hardening steels, have received a great deal of attention since they offer superior tensile properties along with good dimensional accuracy due to their unique processing route consisting of high temperature forming within austenite region followed by cooling in a die to form low temperature hard phases such as martensite or bainite 6 – 8 . However, such a processing route has a poor production efficiency and moreover these HPF steels generally suffer from liquid metal embrittlement (LME) or microcracking due to an interaction between coating and substrate during high temperature forming 9 – 14 .…”