Effects of structural inhomogeneities on the steel balls resistance to loading

When conducting impact tests of protective glasses, nonunique cases of destruction of balls made of bearing steel ShKh15 were recorded. The causes of their destruction were determined. The state of the material was studied by fractographic and metallographic analysis, hardness and microhardness measurement. In the structure of the metal of all the balls, no critical defects were found such as flockens, shells and microcracks, but adverse factors were detected in the microstructure of the material, namely, the presence of fineneedle martensite with excessive carbides. It is established that the detected structural factors lead to liability to brittle fracture, an increase in the hardness of the material, a decrease in plasticity. To prevent brittle fracture of the balls and provide a reserve of plasticity of steel ShKh15 at high shock loads assessment calculations of ductility coefficient were made; and it was recommended to limit the maximum hardness of the material critical value HV=5.70 HPa (54 HRC), with the corresponding plasticity coefficient equal to 0.8.

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Study of the process of rolling steel balls in skew rolling mill – metallographic analysis

Technical Sciences ◽

10.31648/ts.6814 ◽

2021 ◽

Vol 24 (1) ◽

Author(s):

Piotr Chyła

Keyword(s):

Rolling Mill ◽

Rolling Process ◽

Dark Field ◽

Bearing Steel ◽

Metallographic Analysis ◽

Modified Method ◽

Microscopy Technique ◽

Cooling Media ◽

Steel Balls ◽

Skew Rolling

This paper presents the results of metallographic research studies carried out for stock materials as well as the samples collected from the balls formed in the rolling process in a skew rolling mill. The stock material was bearing steel 100Cr6 and the steel from rail scrap. The rolling process was carried out in parallel for the two assumptions: the conventional method (hereinafter referred to as conventional rolling) and the modified method (hereinafter referred to as modified rolling). After the rolling process, three cooling media were used: air, water and oil. The pictures below, which depict microstructures, were taken using the bright-field and the dark-field microscopy technique, the samples were etched with a 4% solution of picral.

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Research on Brittle Fracture of X70/X80 Line Pipes with Big Wall Thickness at Low Temperature

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.795.3 ◽

2019 ◽

Vol 795 ◽

pp. 3-8

Author(s):

Hai Tao Wang ◽

Shi Li Li ◽

Yan Long Luo ◽

Jun Qiang Wang ◽

Hai Bin Zhang ◽

...

Keyword(s):

Low Temperature ◽

Brittle Fracture ◽

Wall Thickness ◽

Impact Energy ◽

Charpy Impact ◽

High Rate ◽

Steel Pipe ◽

Thickness Effect ◽

Structural Factors ◽

Charpy Impact Energy

Based on research of the low temperature fracture property of high grade steel pipe, it shows that X70, X80 steel pipe and X80 tee have high Charpy impact toughness. However, as the wall thickness increases, the shear area of DWTT decreases rapidly, and the thickness effect is significant. The research results show that the original wall thickness impact specimen fracture of steel pipe may not be ductile, for design temperature less than -30°C and wall thickness greater than 40mm. The brittle fracture was caused by structural factors. The Charpy impact energy, which just reflects the toughness of materials, does not show the fracture appearance as it would occur in service, because of the different specimen geometry and high rate of impact. The brittle fracture can occur at low temperature and low stress even with a high Charpy impact energy, the conditions of brittle fracture should be established under combination of the wall thickness, temperature and other factors. In this work, it is clarified that measurement of the fracture toughness under service temperature should be used to control low stress brittle fracture, besides the Charpy impact energy to ensure the material toughness.

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Analysis of Damage of Solder Joint of Heat Exchanger

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.270.63 ◽

2017 ◽

Vol 270 ◽

pp. 63-67

Author(s):

Pavel Gejdoš ◽

Lenka Klakurková ◽

Martin Juliš ◽

Miroslava Horynová ◽

Lucie Páleníková ◽

...

Keyword(s):

Heat Exchanger ◽

Solder Joint ◽

Austenitic Steel ◽

Metallographic Analysis ◽

High Alloy ◽

Pressure Test ◽

The Subject ◽

Microstructure Of The Material ◽

Soldered Joint ◽

Eds Microanalysis

The paper focus on the metallographic analysis of damaged heat exchanger made of high‑alloy austenitic steel by soldering. The object in question is a soldered joint of main mounting plate of the heat exchanger and first heat exchanging plate of it. In this part of the heat exchanger after the vibration and pressure test crack appeared. The subject of the analysis is the evaluation of the microstructure of the solder joint (high-alloy austenitic steel and copper), and evaluation of the appeared crack. The problematic is solved with aid of metallographic analysis of the microstructure of the material, using light microscopy and scanning electron microscopy and the EDS microanalysis of chemical composition.

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TiC/a-C Nanocomposite Coatings for Low Friction and Wear Resistance

Materials Science Forum ◽

10.4028/www.scientific.net/msf.475-479.3655 ◽

2005 ◽

Vol 475-479 ◽

pp. 3655-3660 ◽

Cited By ~ 4

Author(s):

Y.T. Pei ◽

Damiano Galvan ◽

Jeff T.M. de Hosson

Keyword(s):

Wear Resistance ◽

Friction And Wear ◽

Ambient Air ◽

Bearing Steel ◽

Nanocomposite Coatings ◽

Columnar Microstructure ◽

Low Friction ◽

Micro Cracks ◽

Steel Balls ◽

Wear Tests

TiC/a-C:H nanocomposite coatings have been deposited by magnetron sputtering and are composed of 2-5nm TiC nanocrystallites well separated by amorphous hydrocarbon (a-C:H) of about 2nm separation width. A transition from columnar to glassy microstructure has been observed with increasing substrate bias or carbon content. Micro-cracks induced by nanoindentation or wear tests readily propagate through the column boundaries whereas the coatings without a columnar microstructure show supertough behavior. The nanocomposite coatings exhibit hardness of 5~20 GPa, superior wear resistance and strong self-lubrication effects with a friction coefficient of 0.05 in air and 0.01 in nitrogen under dry sliding against uncoated bearing steel balls. Especially, the transitions from low to ultralow friction or the reverse are repeatedly switchable if the atmosphere is cycled between ambient air and nitrogen. The lowest wear rate is obtained at high humidity.

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Experimental Research on the performance of HIGH temperature bearing steel Cr4Mo4V

Recent Patents on Mechanical Engineering ◽

10.2174/2212797614666210525115618 ◽

2021 ◽

Vol 14 ◽

Author(s):

Zenan Chu ◽

Qiang He

Keyword(s):

Tensile Strength ◽

High Temperature ◽

Friction Coefficient ◽

Three Dimensional ◽

Hardness Test ◽

Surface Friction ◽

Bearing Steel ◽

Metallographic Analysis ◽

Element Analysis ◽

Friction Resistance

Background:: The Cr4Mo4V steel is widely used in high temperature bearings because of its excellent high temperature performance. According to the research status of Cr4Mo4V at home and abroad, this paper explores its mechanical properties and friction properties at high temperatures. Objective:: To characterize the composition, microstructure and properties of Cr4Mo4V steel and to explore its tensile properties, hardness and friction properties at high temperature. Methods: Many methods are adopted, such as chemical element analysis, metallographic analysis, hardness test, tensile test, damping test, friction test and so on. Results: The microstructure of Cr4Mo4V is tempered martensite. The hardness and maximum tensile strength of Cr4Mo4V decrease with temperature increasing. The grain of the Cr4Mo4V steel after heating gets refined and the grain boundary increases. At room temperature, the surface friction coefficient and wear rate of Cr4Mo4V steel decreases. Moreover, Cr4Mo4V steel-ceramic ball shows the best friction resistance. At high temperature, the friction coefficient and the wear of Cr4Mo4V steel firstly decrease with temperature increasing and then increase sharply at 200°C. Conclusion: With the increase of temperature, the hardness, breaking force and tensile strength of Cr4Mo4V bearing steel decrease, whereas the friction property increases. By analyzing the three-dimensional morphology of different wear samples, the optimal working temperature of Cr4Mo4V steel for bearing is 200°C.

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Stability of the surface layer of bearing steel ShKh15

Metal Science and Heat Treatment ◽

10.1007/bf00664193 ◽

1975 ◽

Vol 17 (6) ◽

pp. 532-534

Author(s):

A. G. Ran'kova ◽

V. S. Kortov ◽

M. L. Khenkin ◽

A. I. Gaprindashvili ◽

G. M. Guseva

Keyword(s):

Surface Layer ◽

Bearing Steel ◽

Steel Shkh15

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Fatigue Life of High-Speed Ball Bearings With Silicon Nitride Balls

Journal of Lubrication Technology ◽

10.1115/1.3452596 ◽

1975 ◽

Vol 97 (3) ◽

pp. 350-355 ◽

Cited By ~ 21

Author(s):

R. J. Parker ◽

E. V. Zaretsky

Keyword(s):

Fatigue Life ◽

Silicon Nitride ◽

High Speed ◽

Bearing Steel ◽

Rolling Element Bearing ◽

Ball Bearings ◽

Rolling Element ◽

Low Mass ◽

Element Bearing ◽

Steel Balls

Hot-pressed silicon nitride was evaluated as a rolling-element bearing material. This material has a low specific gravity (41 percent that of bearing steel) and has a potential application as low mass balls for very high-speed ball bearings. The five-ball fatigue tester was used to test 12.7-mm- (0.500-in-) dia silicon nitride balls at maximum Hertz stresses ranging from 4.27 × 109 N/m2 (620,000 psi) to 6.21 × 109 N/m2 (900,000 psi) at a race temperature of 328K (130 deg F). The fatigue life of NC-132 hot-pressed silicon nitride was found to be equal to typical bearing steels and much greater than other ceramic or cermet materials at the same stress levels. A digital computer program was used to predict the fatigue life of 120-mm- bore angular-contact ball bearings containing either steel or silicon nitride balls. The analysis indicates that there is no improvement in the lives of bearings of the same geometry operating at DN values from 2 to 4 million where silicon nitride balls are used in place of steel balls.

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