Wear mechanisms of coated steels during press hardening

Abstract

In this work microstructure of Al-base coated press-hardening steel 22MnB5, austenitized at
920°C, was analyzed with respect to the phase formation at the steel/coating interface. Thereby,
iron diffusion into the Al-base coating led to the formation of intermetallic Al_xFe_y phases. The
intermetallic phases transformed to more Fe-rich phases with increasing dwell time. The coating
was characterized by a layered structure of phases Al₅Fe₂ and AlFe after a dwell time of t_Aus = 6
min (conventional press-hardening parameters). Cracks were formed in the coating due to the low
fracture toughness of the formed intermetallic phases mainly of type Al13Fe4, Al5Fe2 and AlFe.
Forming and quenching in the press-hardening tools took place at a temperature range of approx.
800°C to room temperature (RT). We found that the high hardness (520-1130 HV) and low fracture
toughness of the intermetallic phases led to strong wear of the press-hardening hot-work tool steel
X38CrMoV5-3. The hardness of the intermetallic phases decreased in the direction of a higher
temperature, leading to less abrasive wear at higher forming temperatures, thus wear by adhesion
is more pronounced. Phase AlFe was found to mainly induce adhesive wear, while phase Al₅Fe₂
led to strong abrasive wear due to the delamination of coating particles.