Study compares properties of water and gas atomised 17-4PH stainless steel for MIM

December 2, 2015

December 2, 2015

17-4PH (precipitation hardening grade) stainless steels are one of the most popular materials used in MIM, offering superior mechanical properties and corrosion performance. This grade of stainless steel is also magnetic and hardenable to various strength levels by varying the aging heat treatment temperature. Ming-Wei Wu at the National Taiwan Institute of Technology and fellow researchers from the National Formosa University, Taiwan and National University Taiwan, have reported on the results of a study, published in Metals and Materials International (Vol. 21, No. 3, May 2015, pp 531-537) to compare the as-sintered and heat treated properties of both water atomised and gas atomised 17-4PH stainless steel powders. The paper, “Microstructures, Mechanical Properties, and Fracture Behaviors of Metal Injection Molded 17-4PH Stainless Steel” focussed in particular on the influence of powder type on various heat treatments (sintering, solutioning, H900, and H1100) on microstructure and mechanical properties. The role of δ ferrite on the fracture behaviour of MIM 17-4PH stainless steels was also examined.

The two grades of 17-4PH stainless steel had a median particle size of 10.3 µm for water atomised (W) powder and 12.0 µm for gas atomised (G) powder. The researchers stated that the minor difference in particle size and size distribution was not expected to play an important role in the densification process and that the properties would be influenced more by the lower silicon and oxygen content and fewer SiO2 inclusions in the gas atomised grade.

Study compares properties of water and gas atomised 17-4PH - 17-4PH

Elongation properties of the two types of MIM 17-4PH as a function of process condition

The two grades of 17-4PH stainless steel powders were kneaded with 7 wt% wax-based binder, comprising paraffin wax, stearic acid and polyethylene and the resultant feedstock injected moulded as per MPIF Standard 50. The organic binder was removed first by immersion in heptane at 45°C for 8 hrs, followed by thermal debinding at 500°C for 2 hrs in a tube furnace under hydrogen. The debound parts were then pre-sintered at 1000°C and final sintering took place at 1350°C in a vacuum furnace under partial pressure of argon of around 500 Pa. The sintered density of W and G grades were 7.58 and 7.66 g/cm3 respectively.

The reason for the lower sintered density in the W grade is said to be the presence of 1.2 vol% SiO2 which decreased the theoretical density of MIM 17-4PH from 7.80 to 7.73 g/cm3 . The microstructures of as-sintered and heat treated parts consisted of martensite and δ ferrite, irrespective of the powder grade, with the fraction of δ ferrite not found to affect final sintered density.

The authors showed that better mechanical properties of MIM 17-4PH stainless steel can be achieved with gas atomised powder than with water atomised powder due mainly to the lower silicon and oxygen contents and fewer SiO2 inclusions in the gas atomised stainless steels. The H900 heat treated 17-4 PH specimens produced the highest hardness (HRC) and ultimate tensile strength (UTS), along with moderate elongation of greater than 8%. These values are higher than those specified in the MPIF Standard. However, H1100 heat treatment produces the best elongation at over 11% (Fig. 1), along with moderate hardness and UTS. This clearly shows that higher property values can be achieved with the gas atomised powder grade. The presence of 10 vol% δ ferrite was found not to impair the UTS or elongation of MIM 17-4PH stainless steels. The δ ferrite did not fracture, even though the neighbouring martensitic matrix was severely cracked.


Spring 2023 issue of PIM International magazine
December 2, 2015

In the latest issue of PIM International…

Download PDF

Extensive MIM, CIM industry and sinter-based AM industry news, plus the following exclusive deep-dive articles and reports:

  • Visottica Group: Integrated workflows and the value of Metal Injection Moulding in eyewear and beyond
  • In MIM’s post-smartphone era, where is China’s Metal Injection Moulding industry going?
  • Ceramic AM at scale: The story of how Steinbach AG scaled production to 12,000 parts a year for Da Vinci Surgical Systems
  • MIM F75 (Co-Cr-Mo) for high-volume production: The impact of sintering conditions on microstructure and properties
  • World PM2022: Research into the Binder Jetting of aluminium, Ni-free stainless steel, hardmetals and metallic glass

The latest news from the MIM, CIM and sinter-based AM industries

Don't miss any new issue of PIM International, and stay up to date with the latest industry news. Sign up to our fortnightly newsletter.

Sign up

Join our community

Discover our magazine archive…

The free-to-access PIM International magazine archive offers unparalleled insight into the world of MIM, CIM and sinter-based AM from a commercial and technological perspective through:

  • Reports on visits to leading part manufacturers and industry suppliers
  • Articles on technology and application trends
  • Information on materials developments
  • Reviews of key technical presentations from the international conference circuit
  • International industry news

All past issues are available to download as free PDFs or view in your browser.


Browse the archive


Looking for suppliers of materials, production equipment and finished MIM, CIM or sinter-based AM parts?

Discover suppliers of these and more in our advertisers’ index and buyer’s guide, available in the back of PIM International.

  • Metal powders
  • MIM, CIM & AM parts producers
  • Binders & feedstocks
  • Feedstock mixers
  • Furnaces & furnace supplies
  • Atmospheres & gas generation
  • HIP systems & services
  • Injection moulding machines
  • AM technology
  • Debinding systems
Download PDF
Share via
Copy link
Powered by Social Snap