Selective laser sintering of the gas atomized M2 high speed steel powder was performed using laser powers of 2.5–100 W, scan rates of 1–30 mm/s and scan line spacings of 0.15–0.75 mm. With increasing laser power, the sintered surface varied from open/closed pores to a fully dense structure. Large lateral pores were found in the sintered surface of samples using high scan rates. For fully dense samples, smooth surfaces could be achieved using large scan line spacing. The as-supplied and sieved M2 powder particles with size ranging from 0.04 to 400 μm and 53 to 150 μm, respectively, were found to give better laser sinterability as compared with those powder particles with finer ( 150 μm) sizes.

Selective laser sintering of gas atomized M2 high speed steel powder

Three high-speed steels (HSSs) M2, ASP23, ASP30 were surface-melted by a CW 2.5-kW Nd:YAG laser. The microstructure of the laser surface-melted HSSs was investigated by optical microscopy, scanning electron microscopy and X-ray diffractometry, and the hardness profiles of the laser surface-melted layers were determined by a Vickers hardness tester. The corrosion behavior in 0.6 M NaCl and 0.5 M NaHCO3 solutions at 25 °C was studied by potentiodynamic polarization technique. Metallographical as well as electrochemical corrosion studies illustrated the beneficial effects of laser surface melting (LSM) in refining the microstructure and in enhancing the corrosion resistance of the HSSs. The large carbide particles of annealed HSSs were dissolved after LSM and ultrafine dendrites of austenite and martensite with submicroscopic carbide precipitation were formed in the melt zones of the laser surface-melted HSSs. LSM of M2, ASP23 and ASP30 produced surface layers of hardness 615, 580 and 665 Hv, respectively. The hardness of the laser surface-melted ASP23 and ASP30 reached about 0.75 to 0.80 that of the conventionally hardened ones, while the hardness of laser-melted M2 was comparable to that of conventionally hardened M2. The corrosion resistance of all laser surface-melted HSSs in both solutions was significantly improved, as evidenced by a noble shift of the corrosion potential and a reduction in the corrosion current density. Among the HSSs, laser surface-melted ASP23 possessed the highest corrosion resistance in both solutions. The presence of cobalt in ASP30 has no beneficial effect on enhancing its corrosion resistance. The enhancement in the corrosion resistance of the laser surface-melted HSSs is attributable to the combined effects of dissociation and refinement of large carbides and the increase of the passivating alloying elements such as Cr, Mo and W in solid solution.

Microstructure and corrosion behavior of laser surface-melted high-speed steels

Liquid phase sintering of M3/2 high speed steel by selective laser sintering

Laser cladding of gas-atomized M2 high-speed steel on the mild steel substrate was performed using scan rates of 1 to 10 mm/s, scan line spacings of 0.1 to 0.5 mm, and powder feed rates of 1 to 10 g/min, for a given laser power of 400 W. This article presents a detailed study of the microstructural evolution during laser cladding. The effect of scan rate, scan line spacing, and powder feed rate on cooling rate can be described in terms of the cladding-layer thickness, i.e., the thinner the layer, the higher the cooling rate. The degree of metastability in the laser-clad microstructure can be understood in terms of the lattice parameter of the bcc phase. The lattice parameter of the bcc phase increased with increasing layer thickness and reached a maximum value at a thickness of 0.3 mm. Correspondingly, the microstructure varied from a cellular or dendritic structure of δ ferrite and austenite to a mixture of martensite and retained austenite. However, further increasing the layer thickness led to a decrease of both the lattice parameters of the bcc phase and the proportion of retained austenite in the martensite. This was accompanied by an increase of the amount of carbide at the prior austenitic grain boundaries and a decrease of the carbon content in the martensite and retained austenite.

Microstructural Evolution during Laser Cladding of M2 High-Speed Steel

https://espace.library.uq.edu.au/view/UQ:410468/UQ410468_OA.pdf

Direct fabrication of high-performance high speed steel products enhanced by LaB6

The role of high-speed steel as a cutting tool material is described. The choice of grades for various applications is strongly influenced by economic considerations as affected by alloy availability and cost. While the heat treatment applied to the finished tool is critical in achieving the desired properties, many factors affecting tool manufacture and use are dependent upon proper control of steel production. The coarse structure of cast ingots necessitates heavy hot-working reductions to achieve an adequate breakdown of primary carbides. Lengthy and expensive process routes are involved. Powder metallurgy techniques can provide an ideal distribution of carbides and many potential benefits are outlined, as are some of the problems encountered. Exploitation appears to have been limited, due to the expensive plant and processes required; consequently, in many applications, use of the products cannot be justified economically. At present, the most significant benefit lies in increasing the availab...

F. A. Kirk

Papers

Problems in High-Speed Steel Manufacture and Use: A Challenge for Economic Powder Metallurgy Processing