M. Windmann, A. Röttger, W. Theisen

Wear mechanisms of coated steels during press hardening

Introduction

Wear mechanisms of coated steels during press hardening. Analyzes wear mechanisms of Al-coated steels during press hardening. Iron diffusion forms hard, brittle intermetallic phases (AlFe, Al5Fe2), causing abrasive and adhesive wear on tools.

Abstract

In this work microstructure of Al-base coated press-hardening steel 22MnB5, austenitized at920°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 AlxFey phases. Theintermetallic phases transformed to more Fe-rich phases with increasing dwell time. The coatingwas characterized by a layered structure of phases Al5Fe2 and AlFe after a dwell time of tAus = 6min (conventional press-hardening parameters). Cracks were formed in the coating due to the lowfracture 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 fracturetoughness of the intermetallic phases led to strong wear of the press-hardening hot-work tool steelX38CrMoV5-3. The hardness of the intermetallic phases decreased in the direction of a highertemperature, leading to less abrasive wear at higher forming temperatures, thus wear by adhesionis more pronounced. Phase AlFe was found to mainly induce adhesive wear, while phase Al5Fe2led to strong abrasive wear due to the delamination of coating particles.

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