Steels for bearings

Microstructure-sensitive computational modeling of fatigue crack formation

Fatigue life of additively manufactured Ti–6Al–4V in the very high cycle fatigue regime

This article extensively reviews published research on inclusions in ingot steel and defects on ingot products, methods to measure and detect inclusions in steel, the causes of exogenous inclusions, and the transport and entrapment of inclusions during fluid flow, segregation, and solidification of steel cast in ingot molds. Exogenous inclusions in ingots originate mainly from reoxidation of the molten steel, slag entrapment, and lining erosion, which are detailed in this article. The measures to prevent the formation of exogenous inclusions and improve their removal are provided, which are very useful for the clean steel production of ingot industries.

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State of the art in the control of inclusions during steel ingot casting

Safe life and damage tolerance aspects of railway axles – A review

Glass formation and phase separation in the Ag–Cu–Zr system

Fatigue tests were conducted on a series of 1800 MPa-class spring steels whose fatigue properties were inclusion controlled. The fatigue tests were conducted on billets and on hot-rolled bars, taking into account the elongation of the oxide-type composite inclusions that were deformed during hot rolling, i.e., controlled inclusions. Anisotropy of the fatigue properties due to the slender shape of the elongated inclusions was also discussed. Fatigue tests were then conducted for both the rolling direction (RD) and transverse direction (TD) in the case of the billets. The fatigue test results in the RD showed a slight difference between billets and bars. The inclusions that were deformed during hot rolling were sufficiently elongated, even for the billet specimens, and differences in the effective inclusion sizes between the billets and their hot-rolled bars for the RD were small. However, there were marked differences in fatigue strength between the RD and TD in the billet specimens: the fatigue strength was almost half in the TD due to the presence of fish-eye fractures originating in large and slender MnS inclusions. In these fatigue tests, the two types of deformable inclusions revealed remarkably different effects on fatigue strength: the deformable oxide-type inclusions never caused fish-eye fracture, although the MnS inclusions found in the billets were extremely detrimental to fatigue strength when stress was applied in the TD.

Inclusion-controlled fatigue properties of 1800 MPA-class spring steels

In this report, we propose a novel inclusion inspection method based on the use of 20 kHz fatigue tests. In these fatigue tests, which take a little time, the most harmful inclusions or internal facets appear automatically at the origin of fish-eye fractures. The novel inclusion inspection employing fatigue tests was demonstrated, in two high-strength steels, to be superior to a conventional inspection by scanning of polished surfaces. Our novel inspection method was first demonstrated with a JIS-SUP12 spring steel that contained relatively large Al2O3 inclusions. The novel inspection method appeared to detect larger Al2O3 inclusions than the conventional inspection, since the inspection volume was 22 times more extensive than that of conventional inspections. On the other hand, there was little difference in the maximum Al2O3 inclusion sizes estimated for several volumes of steel between the novel and conventional inspections. Second an inclusion inspection was conducted on JIS-SCM440 low-alloy steel. For this steel, the discussion focuses on TiN inclusions. Fatigue tests appeared to be the only way of conducting inspections for TiN inclusions, since the inclusions could not be detected in the conventional inspection. In measuring the TiN inclusion sizes, however, etching of the fracture surfaces was found to be absolutely necessary, since the inclusion sizes on the fracture surfaces were significantly different from the true sizes. The difference seriously influenced the estimation of the maximum inclusion sizes. Even in the case of internal-facet-originated type fish-eye fractures etching was found to be necessary, since TiN inclusions occasionally appeared after etching.

A novel inclusion inspection method employing 20 kHz fatigue testing

Effect of mean stress on fatigue properties of 1800MPa-class spring steels

Fatigue tests were carried out at frequencies of 20 kHz, 600 Hz and 100 Hz for low-temperature-tempered SNCM439 steel. Ultrasonic, high-speed servohydraulic and electromagnetic fatigue test machines were used for 20 kHz, 600 kHz and 100 Hz tests, respectively. The fatigue tests showed that fatigue properties were independent of the frequencies, while fatigue lives were distributed in wide range on the S-N diagram. Almost all specimens were broken from internal Al2O3 inclusions of various sizes between 9 and 82 μm. Fatigue lives were found to depend on the inclusion sizes. ODA, i.e. optically dark area, was observed in all specimens broken over 107 cycles. ODA sizes were also independent of the frequencies. The scattered S-N diagram was found to be expressed by an unique curve by normalizing stress amplitudes σa with fatigue limits σ'w estimated by Murakamis equation. The modified S-N diagram showed a clear fatigue limit between 109 and 1010 cycles.

Takayuki Abe

Papers

Glass formation and phase separation in the Ag–Cu–Zr system

Inclusion-controlled fatigue properties of 1800 MPA-class spring steels

A novel inclusion inspection method employing 20 kHz fatigue testing

Effect of mean stress on fatigue properties of 1800MPa-class spring steels

Effect of Frequency on Giga-Cycle Fatigue Properties for Low-Temperature-Tempered SNCM439 Steel