State‐of‐the‐Knowledge on Coating Systems for Hot Stamped Parts

Abstract

In the present contribution, recent developments of coatings for hot stamped steels are reviewed. The use of bare steel in the initial hot stamping technology is discussed, including the application of lubricant oils which are used as oxidation inhibitors on bare steel surfaces. The aluminized coatings are introduced, focusing on the microstructure evolution of aluminized coatings during the hot stamping process. An analysis of the cracking of the coating, caused by the formation of brittle Fe-Al intermetallic phases and their high temperature deformation, is presented. The development of a ductile aluminide coating formed during the diffusion treatment of an aluminized coating is discussed. This aluminide coating can endure both high temperature oxidation and severe plastic deformation. The recently developed galvanized and galvannealed coatings are also reviewed and the influence of the gas atmosphere during the heating cycle on the coating stability is emphasized. The solutions which have been proposed to avoid liquid Zninduced embrittlement are analyzed. The use of Zn-Ni alloy coating, which is characterized by a higher melting temperature, is reviewed. The behavior of sol-gel hybrid coatings on hot stamped steels is discussed. The possible use of the recently developed Al-Zn alloy coatings, dual layer Zn-Al and Zn-Al-Mg coatings is also introduced. The application of Zn-Al-Mg post-process galvanizing is also discussed. In each case, all available information related to the weldability, paintability, and corrosion resistance of the coating systems is also reported. Finally, the advantages and technical challenges associated with each type of coating are reviewed.[ Ã ] Dr.

Characterization of the Bendability of Press‐Hardened 22MnB5 Steel

“…[14] In a hot stamping line, PHS with different coating systems is used to avoid the harmful influence of the oxidation and decarburization on the surface appearance and the mechanical properties of the parts. [15] As the bending response of a PHS part depends on its surface properties, these two phenomena are expected to have an important impact on the bendability of an uncoated press-hardened part, which would not be as apparent by testing the PHS in a uniaxial tensile test. Generally, the bendability is defined by the ratio of sheet thickness to punch radius, which can endure a specified bending operation without fracture.…”

Study of the Corrosion Behaviour, Liquid Metal Embrittlement and Resistance Spot Weldability of Galvannealed Hot Stamping Steel

“…핫스탬핑용 강판으로는 22MnB5 (0.22C-1.25Mn-0.002B, wt%) 가 주로 사용되며, 일반강판 대비 C, Mn, B 등의 경화능 원소를 많이 포함하고 있어 냉각 후 마르텐사이트 조직을 안정적으로 확보할 수 있다 [7]. 핫스탬핑 강판은 고온 열처리를 필요로 하기 때문에 고온산화 및 탈탄 방지 를 위한 도금이 필수적이다 [8]. 가장 보편화된 도금은 Al-10 %Si 합금으로 열처리 시 우수한 Barrier Protection 을 제공한다.…”

Phase Formation during Heat Treatment of Zn‐ and ZnAlMg‐Coated Steels at 400 and 750 °C

“…In comparison to conventional Zn‐coated and cold‐formed parts, AlSi‐ or ZnFe‐coated and hot‐formed components do not show sufficient cathodic corrosion protection, which would be necessary for applications in wet regions of the bodywork . This can be explained by the formation of brittle intermetallic Al–Fe or Zn–Fe phases in the coatings during the hot‐forming process (880–950 °C), which is accompanied by the absence of the free zinc − this element mainly determines the cathodic corrosion resistance. A further problem is that ZnFe coatings melt during hot‐forming at 880–950 °C due to the low melting point of Zn‐ and Zn–Fe intermetallic phases (max.…”