Capsule-free hot isostatic pressing of sintered steel to full density using water atomised iron and Cr-alloyed powder consolidated by cold isostatic pressing

ABSTRACT

Powder metallurgy (PM) steel with enhanced density is essential for meeting the demands on high strength and high-performance applications. In this study, cold isostatic pressing (CIP) is applied for consolidating water-atomised iron and Cr-alloyed steel powder to reach about 95% densification before sintering. Additionally, the effect of the lubricant and graphite addition on the compressibility of the different base powder types was evaluated. The maximum green densities of ≈7.55 g cm⁻³ for iron powder and ≈7.45 g cm⁻³ for Cr-alloyed powder were reached after CIP at 800 MPa. The sintering at 1250°C with added graphite allowed to achieve increased densification to ≈7.60 g cm⁻³ for the iron and ≈7.50 g cm⁻³ for Cr-alloyed grades, respectively. These levels were sufficient for surface pore closure, which allowed the application of the capsule-free hot isostatic pressing (HIP) after sintering to reach full density. This approach paves the way for manufacturing large-sized PM components.

KEYWORDS:

• PM steel
• cold isostatic pressing
• sintering
• capsule-free hot isostatic pressing
• full density

Acknowledgements

The authors would like to acknowledge the funding from Vinnova (Swedish Agency for innovation systems) for the project ComPreSint as well as the projects DENSE-PM and DENSE within the framework of the innovation programme Metallic Materials. The authors greatly acknowledge support from the Chalmers Area of Advance in Production and the strategic innovation programme LIGHTer, supported by Vinnova.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by VINNOVA (SE): [grant number 2013-03299]; Vinnova: [grant number 2018-02371]; Vinnova: [grant number 2017-02531].

Notes on contributors

Maheswaran Vattur Sundaram

Maheswaran Vattur Sundaram received his Ph.D. degree in material science in 2019 from Chalmers University of Technology, Sweden, focussed on the full densification of PM steels. Currently working at Höganäs AB as a Material Development Engineer.

Eduard Hryha

Eduard Hryha received his Ph.D. degree in materials engineering in 2008 from the Institute of Materials Research of the Slovak Academy of Sciences, Slovakia. He is currently a Professor at the Department of Industrial and Materials Science, Chalmers University of Technology. His main research activity is devoted to powder metallurgy and additive manufacturing.

Magnus Ahlfors

Magnus Ahlfors received his Master of Science in materials engineering in 2012 from Chalmers University of Technology, Sweden. He is currently working at Quintus Technologies AB, Sweden, as a Business Development Manager.

Ola Bergman

Ola Bergman (1969–2019) received his Ph.D. degree in material science in 2011 from Chalmers University of Technology, Sweden. He had worked extensively within the PM field for more than 20 years contributing significantly to the development and growth of PM steels. He was working at Höganäs AB as a Manager Material Development and now he is no more.

Sigurd Berg

Sigurd Berg received his Master of Science in materials science in 1994 from KTH Royal Institute of Technology, Sweden. He is currently working at Höganäs AB as a Vice President Technology and Development.

Lars Nyborg

Lars Nyborg received his Ph.D. degree in surface engineering in 1987 from Chalmers University of Technology. He is currently a professor at the Department of Industrial and Materials Science, Chalmers University of Technology. His main research activity is devoted to surface science, powder metallurgy, and additive manufacturing.