In situ observation of rolling contact fatigue cracks by laminography using ultrabright synchrotron radiation

Abstract

In rolling contact fatigue (RCF), cracks usually initiate from inclusions beneath the surface and propagate to the contact surface. In the present study, synchrotron radiation computed laminography (SRCL) imaging was performed to observe flaking defects during the RCF of a high-strength steel. Specially fabricated inclusion-rich steel plate specimens were employed in the experiments. For the in situ observation of crack propagation, a compact RCF testing machine was developed, and a 4D analysis scheme was applied to the data obtained by SRCL. RCF tests were carried out near the measurement hatch of the beam line used SRCL to enable the successive observation of crack initiation and growth behaviors. Specimens before and after the occurrence of flaking were observed by SRCL, and flaking defects and cracks under the surface were successfully detected. As a result, details of the crack initiation and flaking process in RCF could be discussed. Shear-type horizontal cracks were found to initiate after the initiation and propagation of tensile-type vertical cracks along inclusions, where the face of the vertical cracks was perpendicular to the rolling direction and rolling surface. Therefore, the formation of vertical cracks is considered to affect shear-type crack formation and flaking, where the shape and length of inclusions also affect the initiation and propagation of vertical cracks.

Inclusion orientation dependent flaking process in rolling contact fatigue observed by laminography using ultrabright synchrotron radiation X‐ray

“…The material was the same bearing steel (modified JIS SUJ2) as that in a previous study, 36 whose chemical composition (in mass %) was as follows: 1.01 C, 0.33 Si, 0.45 Mn, 0.003 P, 0.049 S, and 1.50 Cr, with Fe making up the balance. The steel was not a commercial bearing steel, but it was fabricated in our laboratory to intentionally contain a high concentration of sulfur to enable the observation of crack initiation from stringer‐type MnS inclusions.…”

“…The dimensions of the specimen for SR‐μCL imaging were 10 mm in width, 24 mm in length, and 1 mm in thickness. The thickness of the specimen was determined to allow the transmission of X‐rays with sufficient intensity for imaging 36 . The specimen was quenched at 1103 K for 0.5 h and tempered at 453 K for 2 h. The average dimensions of MnS inclusions were 28.2 μm in length and 12.0 μm in diameter.…”

“…Since the distance between the center of rotation of the motor and the center of the cam was 1.5 mm, the sliding distance of the ball on the specimen was 3.0 mm. A ceramic ball with a diameter of 6.0 mm and Young's modulus of 300 GPa was employed, and the specimen was immersed in napthenic lubricant oil with a kinetic viscosity of 8.46 mm 2 /s to eliminate friction force 36 . The tests were carried out with reciprocating contact, whereas only the preliminary test in rotating contact was carried out to compare these two test procedures for specimens with an artificial hole.…”

“…SR‐μCL imaging was carried out at an undulator beam line of SPring‐8. The experimental setup and the 3D reconstruction procedure are given elsewhere 36 …”

Evaluation of Fatigue Properties under Four-point Bending and Fatigue Crack Propagation in Austenitic Stainless Steel with a Bimodal Harmonic Structure

“…Consequently, the harmonic-structured SUS304L exhibits a lower resistance to fatigue crack growth owing to grain refinement, and the formation of pores is suppressed by MM. In the future, the three-dimensional fatigue crack shape [41][42][43][44][45][46] and the misorientations near the crack initiation site [47][48][49] will be measured for SUS304L with fatigue damage using synchrotron radiation to describe the mechanism of fatigue crack initiation and propagation in greater detail.…”