Kudamatsu, Japan
Kudamatsu, Japan

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Yamane K.,Kohan Kogyo Ltd. | Kawagoishi N.,Kagoshima University | Morino K.,Tokuyama College of Technology | Fukada K.,Kohan Kogyo Ltd.
Key Engineering Materials | Year: 2010

Ultrasonic and rotating bending fatigue tests were carried out for aged and nitrided Ni-base super alloys to investigate the effects of loading frequency and nitriding on fatigue strength. Loading frequencies were 19.5 kHz under ultrasonic and 50 Hz under rotating bending, respectively. Fatigue strength under ultrasonic was higher than that under rotating bending in both alloys. Moreover, in both tests, fatigue strength was improved by nitriding. The increase in fatigue strength by nitriding was large in ultrasonic fatigue. These results were discussed through the successive observation of fatigue process at specimen surface and fracture surface observation. © (2010) Trans Tech Publications, Switzerland.


Morino K.,Tokuyama College of Technology | Kawagoishi N.,Kagoshima University | Yamane K.,Kohan Kogyo Ltd. | Fukada K.,Kohan Kogyo Ltd.
Key Engineering Materials | Year: 2010

In order to investigate the effect of nitriding on the crack initiation and propagation behavior of Ni-base super alloy, Alloy 718, rotating bending fatigue tests were carried out until 108 cycles at room temperature. By nitriding at 500? for 12h, compound layer of about 5μm in thickness was formed and the initiation of a fatigue crack was strongly suppressed causing the increase in fatigue strength. A crack initiated in brittle manner at the compound layer in all of fractures. However the crack propagated in ductile manner controlled by the property of the base alloy. That is, there is no or little influence of nitriding on the crack growth rate of the alloy. © (2010) Trans Tech Publications, Switzerland.


Itaya T.,National College of Technology, Suzuka College | Ishida K.,Tokuyama College of Technology | Kubota Y.,Kohan Kogyo Ltd. | Tanaka A.,National Institute of Technology, Ube College | Takehira N.,Tokuyama College of Technology
Progress In Electromagnetics Research M | Year: 2016

To visualize eddy current distribution (ECD) of an arbitrarily shaped coil arranged parallel to a moving conductor slab, an exact theoretical solution is derived using an analytical method based on the double Fourier transform method. The arbitrarily shaped coil is regarded as a plane coil of a single turn, and both DC and AC excitation currents can be applied. Furthermore, ECD charts are obtained when the conductor slab is moving. We calculate some examples with respect to a circular coil, rectangular coil, and triangular coil and show the effect of coil excitation frequency and speed of the conductor on ECDs. Results show that the eddy current generated in the moving conductor slab is composed of current induced by the excitation frequency and conductor speed. © 2016, Electromagnetics Academy. All rights reserved.


Yamane K.,Kohan Kogyo Ltd. | Ohta A.,Kagoshima University | Kawagoishi N.,Kagoshima University | Morino K.,Tokuyama College of Technology | Fukada K.,Kohan Kogyo Ltd.
Zairyo/Journal of the Society of Materials Science, Japan | Year: 2010

Rotating bending fatigue tests were carried out using a radical nitrided nickel base superalloy, Alloy 718, to investigate the effect of the nitriding on initiation and propagation behavior of a fatigue crack. The nitriding was done for 12h at 500°C and for 20h at 570°C in consideration of practical application. Compound layers were formed on the specimen surface with the thickness of about 4μm and 10μm respectively under these conditions. Hardness of the base alloy was hardly affected by nitriding at 500°C, but it was decreased at 570°C. Fatigue strength increased by nitriding. The increase in fatigue strength was mainly caused by the suppression of a crack initiation through the compound layer. A surface crack in the aged alloy initiated in ductile manner and one in the nitride alloy initiated in brittle manner from the specimen surface. Also, crack growth rate in the alloy was slightly decreased by nitriding at 500°C. but it was accelerated by nitriding at 570°C. © 2010 The society of Materials Science,.


Yamane K.,Kohan Kogyo Ltd. | Morino K.,Tokuyama College of Technology | Fukada K.,Kohan Kogyo Ltd. | Kawagoishi N.,Kagoshima University
Zairyo/Journal of the Society of Materials Science, Japan | Year: 2010

In order to improve the wear and fatigue properties, radical nitriding was applied to Ni-base superalloy, Alloy 718, which is difficult to nitride at low temperature because of its stable passive film. Nitriding conditions selected were at 500°C∼570°C and for 10h∼20h in consideration of practical application. Compound layers formed by these nitriding conditions were 4μm∼10μm in thickness. By nitriding at higher temperature and for longer time, base alloy was softened, though the thickness of compound layer was increased. Wear properties were improved by the nitriding at both of room temperature and 500°C, especially at room temperature. The improvement of wear properties was caused by surface hardening. Moreover, fatigue strength at room temperature increased. The increase in fatigue strength was mainly caused by suppression of fatigue crack initiation due to compound layer. © 2010 The Society of Materials Science,.


Yamane K.,Kohan Kogyo Ltd. | Morino K.,Tokuyama College of Technology | Kawagoishi N.,Kagoshima University | Fukada K.,Kohan Kogyo Ltd.
Zairyo/Journal of the Society of Materials Science, Japan | Year: 2010

Effect of radical nitriding on fatigue strength of Alloy 718 was investigated at room temperature and 500°C under push-pull loading. Nitrided alloy used was with compound layer of 4/mi. Fatigue strength was increased at room temperature by nitriding, though there was no or little difference in fatigue strengths between aged alloy and nitrided one at 500°C. All of fracture occurred from specimen surface in both alloys at room temperature. On the other hand, fracture origins were specimen surface at high stress levels and subsurface at low stress levels in both alloys at 500°C. Surface crack in the aged alloy initiated in ductile manner and the one in nitrided alloy was in brittle manner. The increase in fatigue strength at room temperature was mainly caused by the suppression of crack initiation by compound layer. The reasons for the change in fracture origin from specimen surface to subsurface at 500°C were the suppressions of crack initiation by compound layer in the nitrided alloy and the one of propagation of small crack by oxide induced crack closure effect in the aged alloy. In both of aged and nitrided alloys, fatigue strength at 50Ot was larger than that at room temperature in high cycle region where subsurface fracture occurred. © 2010 The Society of Materials Science,.


Yamane K.,Kohan Kogyo Ltd. | Kawagoishi N.,Kagoshima University | Maeda Y.,Kagoshima University | Morino K.,Tokuyama College of Technology | And 2 more authors.
Zairyo/Journal of the Society of Materials Science, Japan | Year: 2010

In order to investigate the effect of surface treatment on fatigue properties of martensitic type stainless steel, SUS420J2, rotating bending fatigue tests were carried out using the steels surface-treated by three kinds of conditions. The surface treatments tested were CrN coating, radical nitriding and duplex treatment of CrN coating after the radical nitriding, and the results were discussed in comparison with those of quenched and tempered steel. Fatigue strengths were markedly increased by CrN coating, nitriding and duplex treatment. However, there was no or little effect of CrN coating to nitrided steel on the fatigue strength. Surface fracture yielded in quenched and tempered and CrN coated steels, while fractures occurred from inclusions at the subsurface of specimens in nitrided and duplex treated steels. The growth of an internal crack was suppressed at the boundary of fish eye to the direction to specimen surface by the nitriding in nitrided and duplex treated steels. The ligaments between the fish eye boundary and specimen surface showed a brittle fracture in both steels, especially in duplex treated steel there was a few steps on the ligament meaning the coalescence of cracks initiated from droplets at specimen surface and inclusion in subsurface, independently. © 2010 The Society of Materials Science, Japan.


Kawagoishi N.,Kagoshima University | Ohta A.,Kagoshima University | Morino K.,Tokuyama College of Technology | Yamane K.,Kohan Kogyo Ltd. | Fukada K.,Kohan Kogyo Ltd.
Zairyo/Journal of the Society of Materials Science, Japan | Year: 2011

In order to improve the fatigue strength of a nickel base super alloy, Alloy 718, by nitriding, and make clear the crack initiation site in the nitrided alloy, fatigue tests of the plain specimen were carried out under rotating bending. The suitable treatment condition of radical nitriding was investigated from the view points of thickness of the compound layer and strength of the base alloy in combination of nitriding with aging conditions. The selected condition was the combination of treatments of nitriding at 570°C for 20h after aging at 720°C for 8h and then at 620°C for 4h in consideration of practical application. By this treatment, compound layer was formed on the specimen surface with the thickness of about 10μm without softening of the base alloy. Crack initiation was markedly suppressed by the compound layer, causing the increase in fatigue strength. A crack initiated at the base alloy beneath the compound layer. The initiated crack propagated gradually to both directions of the compound layer and the base alloy, though the crack in the compound layer showed a brittle manner. © 2011 The Society of Materials Science, Japan.


Morino K.,Tokuyama College of Technology | Kawagoishi N.,Kagoshima University | Yoshimi S.,Fuji Heavy Industries | Yamane K.,Kohan Kogyo Ltd. | Fukada K.,Kohan Kogyo Ltd.
Zairyo/Journal of the Society of Materials Science, Japan | Year: 2012

Rotating bending fatigue tests were carried out using a radical nitrided nickel base superalloy, Alloy 718, at 500°C, to investigate the effect of radical nitriding on the initiation of a fatigue crack at elevated temperature. The nitriding was conducted after normal double-aging at two different conditions, i.e. at 500°C for 12h and at 570°C for 20h, in mixed gases of hydrogen and ammonia. By the nitriding, compound layers were formed on the specimen surface with the thickness of about 4μm at 500°C and 10μm at 570°C, respectively. Fatigue strength at 500°C was larger than that at room temperature in both nitrided alloys in wide life region. Fracture origins of the nitrided alloys changed from the base alloy beneath the compound layer to the interior of the alloy with decreasing in stress level, causing that S-N curves showed a step wise shape similar to the result of the aged alloy. The crack initiation was suppressed by the compound layer. Fatigue strength was increased by nitriding in the horizontal region in S-N curves where fatigue strength was controlled by the crack initiation and the propagation of a small crack, though the effect of nitriding on fatigue strength was very small in the region where fatigue life was occupied by the growth of a crack, i.e. in the region except for the horizontal one in S-N curves. Although a surface crack in the nitrided alloy propagated in a brittle manner, the crack propagated steadily similar to the one in the aged alloy propagated in a ductile manner. © 2012 The Society of Materials Science, Japan.


Patent
Kohan Kogyo Ltd. and Toyo Kohan Co. | Date: 2011-07-19

Provided are a rinsing agent to produce a hard disk substrate free from remaining abrasive grains as well as a pit defect on the surface thereof and a method for production of a hard disk substrate using such a rinsing agent. A rinsing agent of the present invention is rinsing solution containing colloidal silica as abrasive grains. Letting that the colloidal silica abrasive grains have a concentration C and an average grain size R (C and R are represented in weight % and nm, respectively), the concentration C and the average grain size R of the colloidal silica abrasive grains have a relation matching the following Expression (1): 12.2C+18.2 (1).

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