High‐cycle rotating bending fatigue property in very long‐life regime of high‐strength steels

Abstract

In order to investigate the fatigue properties of high‐strength steels in the very long‐life regime up to over 109 cycles, cantilever‐type rotating bending fatigue tests were carried out for two kinds of high‐strength steels, SUJ2 and SNCM439, which were machined by grinding and finished by electropolishing after grinding. And also, the residual stress on the specimen surface of the ground specimen was examined by X‐ray diffractometer in order to investigate effects of the residual stress on the fatigue properties. From the investigations, the S–N curves clearly have a tendency to decrease again in the longer‐life range over 107 cycles for both types of specimen and for both steels. From observations of fracture surfaces, it was found that fatigue crack origins could be grouped into two types: (i) ‘surface crack origin type’ in the shorter‐life regime and (ii) ‘internal crack origin type’ in the longer‐life regime.

Evolution Mechanisms of MgO·Al₂O₃ Inclusions by Cerium in Spring Steel Used in Fasteners of High-speed Railway

“…Meanwhile, S content was high in the outer part along the width direction. It is concluded that the inclusion is being changed from MgO·Al 2 At last, the shape of inclusions evolved from irregular into spherical rare earths inclusions.…”

“…Li Jun WANG, 1,2) * Yan Qiang LIU, 3) Qi WANG 1,2) and Kuo Chih CHOU The effect of rare earth metal addition on the non-metallic inclusions in spring steel used in fastener of high speed railway was investigated by metallographic examination; SEM-EDS and component analysis, aiming at deform those harmful inclusions to improve service life of spring steel. MgO·Al 2 O 3 inclusions were found in present experimental steel, which is also confirmed by the stability diagram of MgO/ MgO·Al 2 O 3 /Al 2 O 3 from thermodynamic consideration.…”

“…The fatigue failure is the main factors affecting the service life of spring steel used in fastener of high speed railway. 1,2) There are many factors affecting the fatigue life including inclusions, heat treatment, surface quality, corrosion resistance, and microstructure and grain size etc.…”

Subsurface Crack Initiation and Propagation Mechanism under the Super-Long Fatigue Regime for High Speed Tool Steel (JIS SKH51) by Fracture Surface Topographic Analysis

“…The remarkable area formed around the nonmetallic inclusion inside the fish-eye region on the fracture surface was given various names, such as fine granular area (FGA) (1), (9) - (11) and rough surface area (RSA) (14) . The formation mechanism of the GBF area has yet to be elucidated, because it is difficult to directly observe the behavior of subsurface crack initiation and propagation.…”

Fatigue Fracture Characteristics of Ti6Al4V Subjected to Ultrasonic Nanocrystal Surface Modification

“…Their shapes are long and narrow because of the ultrasonic impacts on the surface. EDX (Energy-Dispersive X-ray spectroscopy) results show that they are not typical inclusions, and these high light white areas are nonexistant in un-UNSMed specimens [31][32][33]. An interior crack core of TC4 without severe surface plastic deformation has a circular or elliptical rough area [20].…”