Review: IPMD 14th Edition 2010-2011, 6 pages, 2771 words

Author: Dr Olle Grinder, PM Technology AB, Sweden

PM Technology AB, Drottning Kristinas Väg 48, S-11428, Stockholm, Sweden.

Dr Olle Grinder reviews the powder metallurgy (PM) processing of tool steels and high-speed steels, which offer the advantages of superior tool properties due to the fine grain size and increased homogeneity of the carbide distribution in these materials. Dr Grinder also reviews the production and applications of fully dense Ni-base PM superalloys with the benefit of higher operating temperatures of turbine disks and improved reliability of gas turbine engines.

Introduction

Research and development on powder metallurgy (PM) processing of high-speed steels (HSS) started in the mid-1960s. The objective was to improve the functional properties and performance of HSS in demanding applications, and thus increase the competitiveness of HSS versus cemented carbides primarily in machining operations.

Development focused on the production of fully dense HSS billets and hot worked semi-finished products using the manufacturing route: melting + inert gas (nitrogen) atomization + powder encapsulation + hot isostatic pressing (HIPing) + removal of capsule by machining. More recently the manufacturing process involves directly filling the high alloy powder into capsules from the atomization plant to avoid contamination of the powder (Fig.1).

The main alloying elements in HSS and tool steels are C, Cr, W, Mo, V, Co and sulphur. Carbon content, which can range from ca.1 to 3% has two purposes. It reacts with the carbide forming elements Cr, W, Mo and V to create the hard phases, and dissolves in the iron matrix to influence mechanical properties. In the cold working and plastic moulding grades, most of the important alloys have increased C, Cr, and V content. Table 1 gives the chemical compositions of the main grades of PM high alloy steels. The process route differs between the manufacturers, which can have an influence on the mechanical and functional properties of the HSS and tool steels.

In the gas atomization step the small droplets rapidly solidify during gas atomization to produce a fine uniform carbide microstructure in the particles. This fine microstructure can be maintained after the HIPing and hot working operations resulting in the PM high alloy steels such as tool steels and high-speed steels, having fine, segregation-free, uniform and isotropic microstructure. The well-known problems with coarse and severe carbide segregation in conventional cast and forged high speed steels are thus avoided in PM HSS. See the comparison in Fig. 2.

It was found early in the development of PM HSS and tool steels that they exhibited several advantages as a result of the refined, homogeneous microstructure compared with their cast and wrought counterparts.These included:...............

Further sections of this article include:

• High-speed steels and tool steels
  Press and sintered high speed steels
• PM superalloys
  Powder Production
  Powder Consolidation
  Post-Consolidation Processing

Figures and Tables:

Fig. 1 Schematic of PM production route for PM tool steels. (Courtesy Böhler-Uddeholm Powder Technology, Austria)

Fig. 2 Microstructure of conventional HSS (top) compared with PM HSS (bottom) at the same magnification (black - iron matrix, white - carbides).

Fig. 3 Relationship between bend fracture strength and hardness for HSS, tool steels, cemented carbides and ceramic materials (Courtesy Erasteel Kloster AB).

Fig. 4 Influence of the carbide structure on fracture initiation and bend fracture strength. HSS bar size (Courtesy Erasteel Kloster AB)

Fig. 5a Microstructure of the nitrogen-alloyed tool steel – Vancron 40, containing 20% by volume of (MN,C) and 4% by volume of M6C. (Courtesy Uddeholm Tooling AB, Sweden)

Fig. 5b Uddeholm Tooling AB, Sweden, received an EPMA Award of Merit for its VANCRON 40 PM HSS in 2007 (Courtesy EPMA, UK)

Fig. 6 Valve body in duplex stainless steel. (Courtesy Bodycote Hot Isostatic Pressing, Sweden)

Fig. 7 Plastics screw element (CPM 10V or CPM 290V) (Courtesy Crucible, USA)

Fig. 8 As HIPed gear cutting hob from S390 Isomatrix high alloy steel. (From: ‘PM Materials, Processes and Applications –CD Rom’ published by EPMA 2001. Courtesy Böhler-Uddeholm Powder Technology, Austria)

Fig. 9 “Viking” sword. HIPed composite material based on two high alloyed steels. (Courtesy Damasteel AB, Sweden)

Fig. 10 Intermediate pressure (IP) turbine disk forging made from RR1000 PM nickel base superalloy (Courtesy: Rolls Royce plc)

Fig. 11 HIPed PM net shape centrifugal impeller using process modelling developed by VILS, Russia, and manufactured at the SUE Klimov, Plant, Russia. (Paper presented at 2002 World Congress on Advances in Powder Metallurgy & Particulate Materials, Orlando, and published in Proceedings)

Fig. 12 MIM superalloy parts used in automotive turbochargers as presented by Volker Arnhold, GKN Technology Day, November 2004 (Courtesy GKN Sinter Metals)

Fig. 13 Non-destructive testing of forged/machined PM superalloy turbine disk used in the F110 GE engine for the F16 fighter aircraft. (Courtesy Techspace Aero, Belgium)

Fig. 14 EJ200 turbofan engine for the Eurofighter Typhoon aircraft utilises PM superalloy disk in both the high pressure and low pressure turbine stages. The engines are produced by Eurojet Turbo GmbH – a consortium of MTU Aero Engines, Rolls Royce, Avio and Industria de Turbo Propulsores (Courtesy Eurojet Turbo GmbH)

Fig. 15 NASA Glenn task manager Robert Draper with forgings of small and large aircraft engine disks made from the ME3 PM superalloy to improve engine efficiency and prolong disk life (Courtesy NASA Glenn Research Center)

Fig. 16 As-HIPed Rene95 turbine disks with the as-HIP shape (upper left), sonic shape (upper right), and finished machined disks on the bottom. (Courtesy Crucible Compaction Metals, USA)

Fig. 17 PM Alloy 625 valves used in an oil patch application. (Courtesy Crucible Compaction Metals, USA)

Fig. 18 PM nickel-base superalloy pipe fitting. (Courtesy Crucible Compaction Metals, USA)