Enhancement of Fatigue Endurance by Al-Si Coating in Hot-Stamping Boron Steel Sheet

Abstract

Most structural components undertake cyclic loads in engineering and failures always cause catastrophic economic losses and casualties. In the present work, the phase evolution of Al-Si coating of high-strength boron steel during hot stamping was investigated. Two types of 1500 MPa grade boron steel sheets, one with Al-Si coating and the other without, were studied to reveal the effect on the high-cycle fatigue behavior. The as-received continuously hot-dip Al-Si coating was composed of α(Al), eutectic Al-Si and τ5. After hot stamping at 1193 K, three phases formed in this coating: β2, Fe(Al,Si)2 and α(Fe). The experimental results showed that the endurance limit of the coated steel sheet was 370 MPa under 107 fully reversed tension-compression loading cycles as opposed to 305 MPa in the uncoated sheet. Both the coated and the uncoated specimens showed surface-induced transgranular fatigue fractures. In the uncoated sheet, the fatigue cracks were generated from the decarburization surface, but the Al-Si coating effectively prevented the occurrence of near-surface decarburization during high-temperature hot stamping, and the only cracks in the coated steel sheet were initiated at wire-cutting surfaces.

Tensile-shear fracture behaviour of resistance spot-welded hot stamping sheet steel with Al–Si coating

“…Backscatter electron image (Figure 3(a) upper) and quantitative elemental analyses by WDS (Table 2) reveal that the hot-stamped products of Al–Si coating are composed of a transition layer of α -Fe(Al,Si) (Spot 1), brittle Fe(Al,Si) 2 (Spot 2) and a few Fe(Al,Si) (Spot 3), as reported in Ref. [33]. Meanwhile, the base material of 22MnB5 sheet steel was fully transformed to lath-like martensitic microstructure (Figure 3(a) lower).…”