Towards high performance with Höganäs

Development of new P/M parts has often become reality through material and process development, and close collaboration between powder supplier, part producer and car manufacturer. Höganäs Group has a leading role in these collaborations, which will be even more intensified in the future.

The pursuit of high performance metal powder components through powder and process development is a prioritized R & D area for Höganäs AB. Providing high performance solutions for parts in automotive applications can unlock a huge potential market for powder components. New cost-effective alloy systems, heat treatment and surface densification – that can be used or combined to meet today’s demanding performance requirements.

Chromium alloy systems

Chromium has become an increasingly attractive element in P/M manufacturing, not only for its effect on strength and hardenability, but also because it is a cost-effective alternative to traditional alloying elements.

The Höganäs Group has been studying the potential of chromium as a low-cost alloying element since 1993. Astaloy CrL (1.5% Cr and 0.2% Mo) was launched by the Höganäs Group at PM2TEC 2002, and along with Astaloy CrM (3% Cr and 0,5% Mo) it has become a well established sintered steel.

A study has been carried out in cooperation with Cloyes Gear and Products, a US manufacturer of components and systems for automotive and industrial applications. The company specializes in valve timing components and systems with production at three sites in Arkansas and Oklahoma.

“We found that Astaloy CrL can provide equivalent or better performance, but at a lower cost than FLN2-4405, alloyed with 2% Ni and 0,8% Mo, according to the MPIF standard,” says Ulf Engström, Technical Director at North American Höganäs. ”Astaloy CrL is a versatile material with a broad appeal that can be used to cover a wide spectrum of requirements in new or existing applications.”

Enhancing properties

Many high-performance components such as gears require a hard surface and a tough core. These properties are commonly achieved by case hardening operations, which aim to improve the fatigue strength and wear resistance of P/M components. In the case of a material pre-alloyed with chromium such as Astaloy CrL, vacuum-carburizing is an interesting means to improve properties with low risk for oxidation of the material during processing.

“One of the many reasons for the growing interest in chromium as an alloying element is the excellent mechanical properties attainable both in the as sintered condition and after secondary heat treatment, such as through hardening or case hardening,“ says Ulf Engström.

Vacuum-carburization of materials based on Astaloy CrL significantly increased tensile strength, transverse rupture strength and hardness compared to the as sintered material. These properties are further enhanced at higher densities.

Some impressive gains were recorded. Tensile strength after vacuum-carburizing increased about 40 % for the material sintered at 1120°C. It also gives dramatically increased hardness at all densities, and values up to 40 HRC was obtained after quenching and tempering. Vacuum-carburization was thus shown to be an effective process to case harden spur gears made of Astaloy CrL with a carbon content in the range of 0.2 to 0.3 %.

“This adds to the growing body of evidence that Astaloy CrL is a cost-effective material that can, with the right processing solutions, deliver properties such as high fatigue strength that are required in automotive gears and other high performance applications,“ concludes Ulf Engström.

Gearing up the future

“We have worked on different parts with Volvo for many years to find ways to meet performance requirements. And we have also enjoyed a long-term relationship in developing technology with Scania,” says Sven Bengtsson of Höganäs AB.

The new study investigates the effects of selective densification on the gear teeth of helical and spur gears. A process route consisting of compaction, sintering, surface densification by rolling and finally heat treatment was used to assess the feasibility of producing transmission gears by powder metallurgy. Tests on the gears focused on densification, gear quality and tooth root fatigue.

“The results were good. Using this material we have managed to achieve the required gear quality with sufficient densification. Astaloy CrL was found to be highly suitable for surface densification.”

“Cooperation with end users such as Volvo and Scania has given us an opportunity to really understand their processes and improve our material development. The more we understand the processes, the more we will be able to develop solutions for surface densified parts that are cost-competitive and meet stringent end user requirements,” continues Sven.

“I see a need for the powder producers, component manufacturers and automotive manufacturers to work even closer together in the future. It is only by fully leveraging the combined competencies that the complete potential for future growth can be harnessed,” says Alrik Danielson, CEO of Höganäs AB.

Höganäs AB
SE-263 83 Höganäs
Sweden
Phone: +46 (0)42 33 80 00
Fax: +46 (0)42 33 81 50
www.hoganas.com