Used successfully in US Space Shuttles
The fuel pumps of US space shuttles - where only liquid oxygen or hydrogen were available as a lubricant - were the decisive test. In trials CRONIDUR® 30 bearings withstood more than 40 start cycles whereas previous models had to be exchanged after each start.
In all trials with bearings, fully lubricated CRONIDUR® 30 achieved a service life which exceeded the calculated value 80 times over. Even when lubrication was inadequate the service life was c. 1,300 hours. This figure is comparable with the M50 and SAE 52100 alloys when they are fully lubricated.
Conventional steels for bearings such as M50 and AISI 440C contain primary, linear-directed carbide with a maximum length of 60 μm. The nitrogen-alloyed steel CRONIDUR® 30, in contrast, boasts a fine and even microstructure, with a maximum carbonitride size of 10 μm.
Outstanding corrosion resistance
The chemical strain on bearings frequently occurs due to condensation which forms when the bearing is not in use. Also in terms of corrosion resistance, tests strongly support nitrogen-alloyed martensitic steels. In the salt spray test the surface of the AISI 440 C steel showed visible corrosion pits, whereas CRONIDUR® 30 showed no signs of corrosion damage.
This nitrogen containing stainless steel has very good fracture toughness and high strength at the same time in combination with excellent corrosion resistance in the hardened state at temperatures of approximately 450°C.
Broad spectrum of application
Martensitic nitrogen steels are also used for the bearings of main driving shafts of large aircraft engines. Because of this unique combination of outstanding properties, the Cronidur® 30 is well-established in both high-performance aerospace applications, general engineering, medical, pharmaceutical and food technology, as well as manufacturing high-end consumer goods in a variety of industries. CRONIDUR® 30 belongs to the generation of steels which convince on account of their material properties and versatility for a diverse range of applications.