Dennis W. Hetzner

Refining carbide size distributions in M1 high speed steel by processing and alloying

The distributions of carbides in M1 high speed steel (HSS) manufactured by four different types of processing will be considered. For conventionally processed ingot steel, the characteristic microstructural features in ingots, intermediate size products and smaller bar product will be discussed. The carbide size distributions in steel bars made by gas atomized powders will be shown. The refinement of the carbides in M1 by using a patented laser glazing process will be illustrated. The last topic is the development of a new patent-pending family of low carbon high speed alloys that can easily be carburized by conventional processing. Various beneficial effects that these alloys provide will be discussed.

Laser-Clad NiAICrHf alloys with improved alumina scale retention

A new mechanism for the improved retention of alumina scales formed on laser-clad NiAICrHf alloys has been observed. Laser cladding is the process where fine metal powders are rapidly melted and fused to a solid substrate using a CO2 laser. The effects of laser cladding upon scale retention on NiAICrHf alloys after cyclic and isothermal exposure to air were investigated using thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The calculated compressive stress in the scale due to constrained cooling exceeded the probable compressive strength of alumina. Additions of up to ≈ 2.5 wt pct Hf increasingly promote retention of scales grown at 1200 °C, with laser-clad samples of ≈ 2.5 wt pct Hf alloy retaining almost completely intact scales. The improvement in scale retention is due to improved toughness in scales containing hafnia polycrystallites, possiblyvia microcracking initiated by anisotropic thermal contraction of the hafnia. Laser cladding the 2.5 wt pct Hf alloy provides a large concentration of ~ 1 µm Hf-rich particles that are precursors of the hafnia in the scale as well as a finer dendrite spacing that reduces the mean free distance between particles.

A metallurgical analysis of laser-clad H13

Rapid prototyping and rapid manufacturing processes are being employed to decrease the time required to develop new products. Laser cladding can be used to produce metal parts directly from CAD drawings. To apply this technology, multiple layers of metal clad are first deposited on a substrate. The clad is then tempered or annealed at periodic stages throughout the buildup process and also prior to machining. The component is then hardened and tempered by conventional heat treating procedures and ground or machined to final size. This investigation considers the response of the clad and base metal to this series of processing variables. H13, an air hardening die steel, was selected for the clads and the base metal. This alloy is commonly used for hot working dies. The response of the clad and substrate to the various heat treatments was evaluated.