The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Machinability Effects of Stainless Steels with a HIPed NiTi Coating in High-Efficiency Machining Operations

Jukka Paro

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Mechanical Engineering for public examination and debate in Auditorium K216 at Helsinki University of Technology (Espoo, Finland) on the 20th of October, 2006, at 12 noon.

Overview in PDF format (ISBN 951-38-6854-0)   [2976 KB]
VTT Publications 610, ISSN 1455-0849

Dissertation is also available in print (ISBN 951-38-6853-2)
Copyright © 2006 VTT Technical Research Centre of Finland
VTT Publications 610, ISSN 1235-0621
VTT-PUBS-610
TKK-DISS-2197

Abstract

The machinability effects of new high-strength stainless steels are researched due to specific properties arising from their structure. In grinding operations, HIPed (Hot Isostatically Pressed) austenitic 316L, duplex 2205 and super duplex 2507, and as-cast 304 stainless steel, in turning HIPed 316L, duplex stainless steel 2205 and X5 CrMnN 18 18 stainless steel, and in drilling HIPed PM (Powder Metallurgic) Duplok 27 and duplex stainless steel ASTM8190 1A and X2CrNi 1911 with HIPed NiTi coating were researched in revised machining testing environments using tool life testing, chip and workpiece surface morphology analysis. Chips, workpiece surfaces and cutting tools were analysed by SEM and EDS.

High toughness, workhardening and low heat conductivity have a synergistic effect in inducing machinability difficulties e.g. decreased product quality, shorter tool life, increased power consumption and decreased chip evacuation. An increased amount of alloying elements is found to decrease machinability in the form of increased cutting force and workhardening rate of the machined surface, and decreased tool life and surface roughness. Also, the machinability of PM-produced stainless steels is decreased because of the increased amount of hard oxide particles included in the microstructure of PM-produced stainless steel. The formation of BUE (Built-up Edge) is found, affecting the machinability and tool life of tested high-strength stainless steels.

In grinding operations HIPed austenitic 316L and duplex 2205 stainless steel are rated according to cutting force, workhardening rate and the amount of microvoids and microcracks in ground surfaces. In turning operations HIPed 316L, duplex stainless steel 2205 and X5 CrMnN 18 18 stainless steels are assessed in machinability order. The machinability of conventional cast duplex stainless steel ASTM8910 and HIPed duplex stainless steel Duplok27 were sorted according to the PRE-value (Pitting Resistance Equivalent).

Finally in this study, the suitability of coated cemented carbide tools in the drilling of conventionally produced cast stainless steels with HIPed NiTi-coating was investigated. In drilling of difficult-to-cut X2CrNi 19 11 stainless steel with a pseudo-elastic coating, effective cutting parameters that maintain an adhesion layer between the NiTi coating and the stainless steel intact with an advantageous surface finish were generated.

This thesis consists of an overview and of the following 7 publications:

  1. Jiang, L., Paro, J., Hänninen, H., Kauppinen, V., and Oraskari, R. 1996. Comparison of grindability of HIPped austenitic 316L, duplex 2205 and super duplex 2507 and as-cast 304 stainless steels using alumina wheels. Journal of Materials Processing Technology 62 (1996), pp. 1-9. © 1996 Elsevier Science. By permission.
  2. Jiang, L., Hänninen, H., Paro, J., and Kauppinen, V. 1996. Active wear and failure mechanisms of TiN-coated high speed steel and TiN-coated cemented carbide tools when machining powder metallurgically made stainless steels. Metallurgical and Materials Transactions A, Vol. 27 A, September 1996, pp. 2796-2808.
  3. Paro, J., Hänninen, H., and Kauppinen, V. 2001. Tool wear and machinability of X5 CrMnN 18 18 stainless steels. Journal of Materials Processing Technology 119 (2001), pp. 14-20. © 2001 Elsevier Science. By permission.
  4. Paro, J., Hänninen, H., and Kauppinen, V. 2001. Tool wear and machinability of HIPed P/M and conventional cast duplex stainless steels. Wear 249 (2001), pp. 279-284. © 2001 Elsevier Science. By permission.
  5. Paro, J. A., Gustafsson, T. E., and Koskinen, J. 2004. Drilling of conventional cast stainless steel with HIPed NiTi coating. Journal of Materials Processing Technology 153-154 (2004), pp. 622-629. © 2004 Elsevier Science. By permission.
  6. Paro, J. A., Gustafsson, T. E., and Koskinen, J. 2003. Chip morphology in drilling of conventional cast stainless steel with HIPed NiTi coating. Proceedings of the 3rd International Conference on Research and Development in Mechanical Industry (RaDMI 2003), Hotel Plaža, 19-23 September 2003, Herceg Novi, Serbia and Montenegro. 8 p.
  7. Paro, J. A., Gustafsson, T. E., and Koskinen, J. 2005. Deformation effects on the interface between X2CrNi 19 11 stainless steel and HIPed NiTi coating in machining. Proceedings of the 18th International Conference on Production Research, 31st July - 4th August 2005, Salerno, Italy. 5 p.

Keywords: stainless steels, machinability, machine tools, wear, surface coating, grinding, turning, drilling, nickel-titanium alloys

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© 2006 Helsinki University of Technology

Last update 2011-05-26