Abstract
AbstractThe high and very high cycle fatigue (VHCF) properties of ultrahigh‐strength Ck45M steel processed by thermomechanical rolling integrated direct quenching were investigated. S–N tests with smooth and small drilled holes containing specimens as well as near‐threshold fatigue crack growth measurements were performed up to 2 × 1010 cycles using ultrasonic‐fatigue testing technique. The fatigue strength of smooth specimens is mainly determined by the size of nonmetallic inclusions. For surface defects larger than 80 μm, the fatigue limit can be correlated with a constant threshold‐stress intensity factor. The ‐parameter model adequately predicts the fatigue limit for internal defects and for surface defects with sizes between 30 and 80 μm. VHCF failures from smaller surface defects occur at stress amplitudes below the predicted fatigue limit. The long‐crack threshold in ambient air is close to the effective threshold stress intensity factor. In optically dark areas at interior inclusions, cracks grow at mean propagation rates of 10−15 m/cycles.
Highlights
Very high cycle fatigue (VHCF) failure is an important issue for high-strength steels
Due to their low defect tolerance, fatigue cracks can even initiate at small inherent defects such as nonmetallic inclusions
Ultrasonic fatigue tests up to more than 1010 cycles were performed with ultrahigh-strength Ck45M steel processed by thermomechanical rolling and subsequent direct quenching
Summary
Very high cycle fatigue (VHCF) failure is an important issue for high-strength steels. Several investigations on the VHCF properties of ultrahigh-strength steels—that is, steels with tensile strengths exceeding 2 GPa—have been performed (e.g., Refs.9–13), the vast majority with bearing steels These studies mainly focus on fatigue fracture emanating from interior inclusions, and several models have been proposed to explain failure at very high number of load cycles.[14,15,16,17,18,19] A relatively seldom considered, but important, aspect with respect to VHCF is that typical low- and medium-alloy ultrahigh-strength steels exhibit rather poor corrosion resistance. Nearthreshold fatigue-crack growth rate (FCGR) measurements were performed, and the threshold-stress intensity factor range considering crack arrest during 1010 cycles was determined Fracture mechanisms for both surface and interior failure are discussed considering environmental influences. It is noted that accumulating 1010 cycles takes more than 6 days, resulting in a measurement time of several weeks for the determined FCGR curve
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Fatigue & Fracture of Engineering Materials & Structures
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
