Our steel mills and the new VTD investment

Clean steel has been a major focus for Ovako for over a century. As a world leading producer of bearing steel, we have seen how our continued improvement in steel cleanness has contributed to the increased lifetime of bearings. The bearing industry was in the vanguard, but today we see an ever-increasing number of new demanding applications appreciating the benefits that clean steel brings. We are confident that this progress will continue. Our three steel mills each have each their own signature when it comes to metallurgical sophistication and casting format. Both these aspects are particularly relevant for making clean steel. At Ovako we can provide the best “fit-for-purpose” steel, by selecting the most suitable steel making route.

Our Hofors mill offers the highest quality level based on advanced ladle metallurgy including degassing and ingot casting. At Hofors we produce IQ-Steel with a cleanness normally only found in re-melted steels. One of the secrets behind this is to crop off the ends of the ingots where potential defects are found. The large casting format also ensures that the final product undergoes significant reduction, deforming any harmful defect in the steel to a size that makes it insignificant. Our Imatra mill has a similar metallurgy but has a continuous caster producing steel blooms. The large bloom size allows for reduction degrees sufficient to ensure good inner soundness of the product. This route is cost effective for producing steel meeting the requirements of demanding bearing applications.

On December 10 Ovako Smedjebacken will host a special introduction event for this large investment of which we are very proud. Please sign up for either of two time slots by using the link below.

Quantifying cleanness in steel

Our biggest challenge in continuing to improve the quality of our steels is to be able to accurately measure the steel cleanness, to quantify it. International standard methods developed many decades ago are becoming more or less obsolete. This is because they are all based on the assessment of a relatively small area. That means the likelihood of capturing the rare defects in clean steel is simply too low. Yet, in the performance of a component we will be able to notice a difference. Simply because in this case a real volume is “tested” and not a small area. This will dramatically increase the probability to find a critically sized defect that can cause a fatigue failure.

Ovako has worked for a long time with different quantification methods to capture the true inclusion distribution across relatively large volumes of steel. Immersed ultrasonic testing at 10 MHz frequency is one method we have implemented as an important quality tool in our production process. Now we have customers who request this testing with agreed limits for what we can detect. We have even published our own open standard for anyone that would like to use it in their own specifications. Please use this link to read and download it.

The Fatigue Calculator – a work in progress

We talk a lot about steel cleanness and inclusions but at the end of the day it is the detrimental effect they have on properties we really are concerned about. The direct relationship between inclusion size and fatigue strength is well accepted and there are several scientific studies showing this. So why not translate the inclusion distribution directly into fatigue performance? We are doing this in a project called the “Ovako Fatigue Calculator”. It will result in a tool that can be used to determine the fatigue properties of a component.