AUTOMOTIVE DESIGN
Fig. 1
properties that can withstand heavy loads in all directions. Tis makes IQ-Steel suitable for complex load cases, such as in gears. Fig.2. shows the results of RBF testing
on different types of steel loaded in both the longitudinal and transverse directions. Depending on the loading mode, both BQ-Steel and IQ-Steel offer an improvement over conventional steel.
TESTING FOR DEFECTS Te conventional approach to testing for defects is centred around destructive testing. However, this limits the sample size and cannot truly verify the mechanical performance. Instead, for clean steel Ovako deploys a portfolio of advanced tests using high-frequency ultrasonics, light optical microscopy (LOM), and scanning electron microscopy (SEM) to verify both the size and distribution of inclusions and defects.
Fig. 1. Relationship between defect size and fatigue strength Fig. 2
IDEAL APPLICATIONS With regard to the ideal applications for these solutions, Ovako is finding that IQ-Steels are already a popular choice for design enigneers working in high-pressure automotive applications. Modern diesel engines, with high and cyclic injection pressures, have proven to be an ideal application. Transmission components are another emerging area of strong interest. Meanwhile, BQ-Steel has been a
valauable problem-solver in the bearing industry for decades now. It is optimised for fatigue strength by a strict control of steel cleanness. Te same approach to fatigue performance is now being applied in many other applications.
Fig.2. Rotating bending fatigue test performance of conventional steel compared with BQ-Steel and IQ-Steel in both longitudinal and transversal direction
designers who have in the past relied on old standards. Modern steel production practices have opened up a new level of performance that makes it possible to downsize or even redesign components. Ovako’s Bearing Quality (BQ)-Steels are high cleanness steels with a reduced defect size. Tis can help improve design life and/
or increase performance. Moderate design changes can also be made while securing high and consistent quality end-user products. Isotropic Quality (IQ)-Steels are designed to have small and isolated inclusions with a cleanness comparable to re-melted steels. Tey have isotropic
ADDING VALUE WITH CLEAN STEEL It is true that clean steel comes at a premium against conventional steel. However, when considering the economics of its use it is important to take a holistic view. Because in many cases, clean steel will increase performance as well as reducing size and weight. Potentially it might even decrease the amount of steel required to manufacture the component. Overall, it is entirely possible for clean steel to provide a cost- efficient solution that adds significant value for critical, highly stressed components.
Patrik Ölund is head of group R&D at Ovako.
www.ovako.com
www.engineerlive.com 11
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