However, at Ovako we never stand still. The best can always get better. Several customers who use our 100Cr6 through-hardening steel in an IQ grade known as 803Q told us they needed even better performance to meet the intense demands of high-stress applications such as components in diesel injector units. So we set out on the quest for IQ-Steel 2.0.
The program
involved extensive research and evaluation to establish the correlation between
key process parameters such as casting and ladle treatment and the resulting
steel cleanliness.
If you
cannot measure it, you cannot improve it; Quantifying micro-cleanliness with
strong statistical resolution is usually one of the most challenging aspects of
understanding and improving steel cleanliness. In this project, a
quantification method based on High Frequency Ultrasonic Scanning (HFUS) was
developed and used to generate data points. Using this data, a correlation was identified
between steel cleanliness and decisive process parameters. The performance was
then evaluated through fatigue testing. In addition, other techniques such as
SEM (Scanning Electron Microscopy) and EDS (Energy Dispersive X-ray
Spectroscopy) were also used to analyze the morphology and chemical composition
of inclusions.
The images below show a non-metallic inclusion at the crack initiation site, which has led to a fatigue fracture.
The project enabled the successful development of a new generation of IQ steel, 2.0,
that offers enhanced cleanliness and performance. The first example is a new
grade of 100Cr6 designated 805Q.
The very significant improvement in cleanness in terms of the consistency and level achieved with 805Q is illustrated in the graph below. In the graph, a lower index value indicates a higher level of cleanliness.
This
translates into the fatigue performance shown in this graph of tests carried
out on samples in small dimensions loaded in the longitudinal direction. It is
clear that the fatigue limit of the IQ2.0 steel has been raised well above IQ steel,
and in some cases, it even approaches ultra clean remelted steel.
We already
have two customers that have placed orders for this new high-quality steel
grade. And we are not stopping there. We are now extending the program to cover
other IQ steel grades, with a specific focus on low-carbon IQ steels in the next
phase of the project.
