Koshiro Mizobe

Homology analysis of structures of high carbon bearing steel: effect of repeated quenching on prior austenite grain size

Abstract To estimate the effect of quenching on metal structures, the analysis process is very important. It was found that use of quenching reduced the prior austenite grain size greatly and the change in compressive stress at the surface of the material had a great effect on its strength. If we can estimate the change of the grains in the structure quantitatively, we can easily evaluate the effect of the quenching process. However, the structures are too complex to apply ordinary image analysis methods. In this paper, we propose a new method for analysing changes in steel structures. By use of this method, we confirm the effect of repeated quenching on the distribution of grains.

Effect of PTFE Retainer on Friction Coefficient in Polymer Thrust Bearings under Dry Contact

Polyetheretherketone (PEEK) is a tough semi-crystalline thermoplastic polymer with excellent mechanical properties. While abilities of polyphenylenesulfide (PPS) are similar to PEEK, former material cost was lower than later. Polytetrafluoroethylene (PTFE) is well known because of its low friction coefficient and self lubrication ability. The objective of this study is to observe the friction coefficient of hybrid bearings, PTFE retainer sandwiched with PPS-races or PEEK-races. Rolling contact fatigue tests were performed and in situ friction forces wear measured. It is concluded that the PTFE retainer reduced friction coefficient.

Observation of non-metallic inclusions on repeatedly quenched SAE 52100 bearing steel fracture surfaces

Martensitic high carbon high strength SAE 52100 bearing steel is one of the main alloys used for rolling contact applications where high wear resistance are required. Due to its high fatigue strength, SAE 52100 is recently being used not only for the production of bearings but also shafts. Refining of prior austenite grain through repeated quenching is a procedure that can be used to enhance the material’s strength. In this work, the microstructure of repeatedly quenched SAE 52100 steel and its fatigue strength under rotating bending were investigated. It was found that repeated furnace heating and quenching effectively refined the martensitic structure and increased the retained austenite content. Repeated quenching was found to improve the fatigue strength of SAE 52100.

Observation of Crack Propagation in PEEK Polymer Bearings under Water-Lubricated Conditions

Radial ball bearings made of metal, ceramics and plastics are commonly used as important components in various types of industrial machinery. Due to the latest markets demands for elements capable of withstanding e.g. corrosive environment, metallic bearings are being gradually replaced by components produced from high performance engineering plastic polymers. In order to investigate the failure mechanism of polymer bearings and further improve their performance in practical applications in an underwater environment, in this research crack propagation in Poly-ether-ether-ketone (PEEK) was studied by rolling contact fatigue (RCF) testing under water. Crack propagation in the inner ring raceway surface and subsurface areas of PEEK bearings after testing was observed by a laser confocal microscope. Cracks and flaking failure were found on the bearing raceway surface. From the RCF tests results, it was found that the detected cracks could be divided into three groups: Main Surface Cracks, Semi-circular Cracks and Main Subsurface Cracks. It is concluded that flaking occurs on the inner ring raceway due to the fusion of semi-circular cracks and a main subsurface crack.

Homology Estimate of Grain Size Measurement Based on the JIS Samples

Test method for measuring austenite and martensite microscopic grain size of the steel is commonly done. Determination of average crystal density for the specimen is defined by JIS (Japanese Industrial Standards) in Japan. In general, this kind of determination is carried out by engineers. The results may depend on their skill, so automated tool to determine the grain size is needed. In this paper we try to apply homology method to analyze the structures. As the first trial, we apply this method to the figures on JIS. The result of homology is compared with the grain size defined in JIS. We can make sure the correlation between grain size and the homology value.

Effect of Thrust Load and Rotation Speed on Wear Loss in PPS Race - PTFE Retainer Hybrid Polymer Thrust Bearings under Dry Contact

In order to establish an optimal material combination for the production of polymer thrust bearings, two types of components: retainer and PPS races - PPS retainer were tested by rolling contact fatigue (RCF). The wear properties of both bearing types were investigated and a relationship between thrust load, rotation speed and wear loss was established. It is concluded that by using a PTFE retainer, it is possible to improve the

The Quantization of the Structure of Fisheyes via Homology Method

Martensitic high carbon high strength SAE 52100 bearing steel is one of the main alloys used for rolling contact applications where high wear resistance are required. Due to its high fatigue strength, SAE 52100 is recently being used not only for the production of bearings but also shafts. In this work, quenched SAE 52100 steel fatigue strength under rotating bending was investigated. Especially, we focus on “fisheye around inclusion” where the fatigue crack starts. Quantitative evaluation of its optical micrograph has not been enough carried out. In order to develop easy evaluation method for the fisheye area, we apply homology technique to the optical observation.

Influence of Repeated Quenching on Bearing Steel Martensitic Structure Investigated by Homology

JIS SUJ2 (high carbon high strength bearing steel) heat treated by repeated quenching was investigated. The microstructure of the bearing traces was observed after heat treatment by laser confocal microscope. In this paper, by mathematical methods, we try to evaluate quantitatively this change of the structure. Homology is a branch of mathematics that allows quantitative describing characteristics of a figure by replacing the figure with algebra. Applying homology we can express the degree of the connection of the figure. Here we use homology to quantify the change of structures by repeated quenching. Keyword: Homology, Rolling contact fatigue, SUJ2, repeated quenching

Observation of Wear on PEEK-PTFE Hybrid Radial Bearings

In this paper, the wear performance of hybrid radial bearing (PEEK-PTFE and alumina ball) was investigated. For effective operation of equipment in clean energy facilities environment, the PEEK-PTFE hybrid bearings was developed. Radial PEEK-PTFE hybrid bearings were produced by machining and their rolling contact fatigue (RCF) behavior under non-lubricated condition was carried out. PEEK accumulation layer with PTFE and graphite appeared on the bearings inner ring under 600-3000 rpm rotation speed. Due to the self-lubrication of PEEK layer, the wear loss of hybrid bearing cycles was lower than in the case of neat PEEK radial bearing. Moreover, It was found that the thin PEEK layer protected the raceway from the friction heat and wear.

Homology Analysis of Prior Austenite Grain Size of SAE52100 Bearing Steel Processed by Cyclic Heat Treatment

Here, we introduce the mathematical methods to quantitatively evaluate the change of the tissue to quenching. SAE 52100 sample was repeatedly quenched and the influence of this cyclic heat treatment was investigated. The repeated quenching process increased the retained austenite content and had little influence on the materials hardness. The prior austenite grain size was decreased and consequently, refinement of the martensitic phase in the material occurred. The higher content of the retained austenite (higher fracture toughness) and the refinement of the microstructure accounted for the higher fatigue properties of the repeatedly quenched material. Here we use mathematical homology to quantify these features.