A case study for a worn tool steel in the hot stamping process

Abstract

A good understanding of failure mechanisms can help us improve the lifetime of the dies. This paper presents a case study investigating the wear behaviour of a QRO90 die insert utilized for stamping uncoated boron-alloyed high-strength steel sheets. Topography and microstructure were characterized by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), hardness measurement and X-ray photoelectron spectroscopy (XPS). Severe galling due to accumulated layers transferred from the boron-alloyed steel workpieces occurred on the die surface. Material softening was detected in the sublayer of the tool steel (up to ∼200 μm). In addition, white layers with a in a thickness of 1–2 μm were frequently observed on the surface of the round corner of the tool. The main wear mechanisms are discussed. Galling caused by surface softening and the spallation of white layers are considered to be the primary wear mechanisms for the tool.

Keywords

• Hot stamping die
• Failure mechanism
• Surface softening
• Transfer materials