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Number of results: 13
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Abstract

The article summarizes the theoretical knowledge from the field of brazing of graphitic cast iron, especially by means of conventional

flame brazing using a filler metal based on CuZn (CuZn40SnSi – brass alloy). The experimental part of the thesis presents the results of

performance assessment of brazed joints on other than CuZn basis using silicone (CuSi3Mn1) or aluminium bronze (CuAl10Fe). TIG

electrical arc was used as a source of heat to melt these filler materials. The results show satisfactory brazed joints with a CuAl10Fe filler

metal, while pre-heating is not necessary, which favours this method greatly while repairing sizeable castings. The technological procedure

recommends the use of AC current with an increased frequency and a modified balance between positive and negative electric arc polarity

to focus the heat on a filler metal without melting the base material. The suitability of the joint is evaluated on the basis of visual

inspection, mechanic and metallographic testing.

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Authors and Affiliations

M. Mičian
R. Koňár
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Abstract

Internal casting defects that are detected by radiography may also be detected by ultrasonic method. Ultrasonic testing allows investigation of the cross-sectional area of a casting, it is considered to be a volumetric inspection method. The high frequency acoustic energy travels through the casting until it hits the opposite surface or an interface or defect. The interface or defect reflects portions of the energy, which are collected in a receiving unit and displayed for the analyst to view. The pattern of the energy deflection can indicate internal defect. Ultrasonic casting testing is very complicated in practice. The complications are mainly due to the coarse-grain structure of the casting that causes a high ultrasound attenuation. High attenuation then makes it impossible to test the entire volume of material. This article is focused on measurement of attenuation, the effect of probe frequency on attenuation and testing results.

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Authors and Affiliations

R. Koňár
M. Mičian
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Abstract

This paper considers the assessment of attenuation in aluminium alloys castings and in cast iron prepared by gravity casting method and by casting under pressure. The issue of ultrasound attenuation is important in setting the conditions of non-destructive (NDT) testing, especially in casted materials. The characteristics of the ultrasonic technique and ultrasonic attenuation and the calculation of the attenuation and the velocity of ultrasound are presented in the theoretical part of this paper. For experimental measurements, cylindrical castings from AlSi alloy (a hypoeutectic alloy with a silicon content of about 7% - AlSi7 and a eutectic alloy with a silicon content of about 12% - AlSi12) and from grey and ductile cast iron were made. The ultrasonic records of the casting control, the calculation of ultrasound attenuation for individual samples are listed and described in the experimental part. The evaluation of measurements and comparison of calculated ultrasound attenuation is at the end of this article.
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Authors and Affiliations

M. Boháčik
M. Mičian
A. Sládek
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Abstract

The article deals with ultrasonic testing possibilities of the copper alloy centrifugal casts. It focused on the problems that arise when testing

of castings is made of non-ferrous materials. Most common types of casting defects is dedicated in theoretical introduction of article.

Ultrasonic testing technique by conventional ultrasound system is described in the theoretical part too. Practical ultrasonic testing of

centrifugal copper alloy cast - brass is in experimental part. The experimental sample was part of centrifugally cast brass ring with

dimensions of Ø1200x34 mm. The influence of microstructure on ultrasonic attenuation and limitations in testing due to attenuation is

describes in experimental part. Conventional direct single element contact ultrasound probe with frequencies of 5 MHz, 3.5 MHz and 2

MHz were used for all experimental measurements. The results of experimental part of article are recommendations for selecting

equipment and accessories for casting testing made of non-ferrous metals.

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Authors and Affiliations

R. Konar
M. Mician
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Abstract

Use of welding technology for the repair of steel castings is particularly common in two areas. These include weld surfacing of protrusions that remained incomplete after casting, or filling the surface defects (cavities). These defects are more common for steel casting than for graphite cast iron, due to the lower fluidity of steel. This article describes a suitable technological process of repairing the defects on the casting using the welding technology. A specimen produced for this purpose was prepared by carving a groove into a cast steel plate 20 GL, which was then filled with a weld metal using MAG (135) technology. The following evaluation of the basic characteristics of the repaired site point to the suitability of the selected technological parameters of the repair procedure. Metallographic evaluation was carried out, further evaluation of mechanical properties by tensile test, bend test and Vickers hardness test. The proposed methodology for the evaluation repair of foundry defects in steel castings also meets the requirements for the approval of welding procedures in accordance with the relevant valid legislation.
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Authors and Affiliations

M. Mičian
J. Winczek
R. Koňár
I. Hlavatý
M. Gucwa
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Abstract

The goal of this article is non-destructive ultrasonic testing of internal castings defects. Our task was to cast several samples with defects like porosity and cavities (where belongs mostly shrinkages) and then pass these samples under ultrasonic testing. The characteristics of ultrasonic control of castings are presented in the theoretical part of this article. Ultrasonic control is a volume non-destructive method that can detect internal defects in controlled materials without damaging the construction. It is one of the most widely used methods of volume non-destructive testing. For experimental control were made several cylindrical samples from ferritic grey and ductile cast iron. Because of the form and dispersion of graphite of grey cast iron it was not possible to make ultrasonic records on this casting with probe we used, so we worked only with ductile cast iron. Ultrasonic records of casting control are shown and described in the experimental part. The evaluation of the measurement results and the reliability of the ultrasonic method in castings control is listed at the end of this article.

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Authors and Affiliations

M. Boháčik
M. Mičian
R. Koňár
L. Trško
J. Winczek
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Abstract

Materials based on cast irons are often used for protection against wear. One of the methods of creating protective surface with cast iron structures is hardfacing. The application of hardfacing with self shielded flux cored wire with high carbon content is one of the economical ways often used to protect machinery parts exposed to both abrasion and erosion. The wear resistance of hardfacings depends on their chemical composition, structure obtained after hardfacing, parameters of depositing process and specific conditions of wear. As the base material in the investigation the steel grade S235JR was used. The wear behavior mechanism of hardfacings made with one type of self shielded flux cored wire and different process parameters were evaluated in this paper. Structures obtained in deposition process were different in hardness, amount of carbides and resistance to wear with two investigated impingement angles. The erosion tests showed that impingement angle 30° gives lower erosion rate than angle 60°.

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Authors and Affiliations

J. Winczek
M. Gucwa
M. Mičian
R. Koňár
S. Parzych
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Abstract

The main goal of the article is to identify artificially created defects like lack of fusion and incomplete penetration in butt weld joint using non-destructive volumetric methods. These defects are the most serious defects in welds of steel constructions from the safety point of view. For identification, an ultrasonic phased array technique and a conventional X-ray using digital imaging were used. The theoretical part of the article describes the current state of the given issue and provides basic theoretical knowledge about ultrasonic and X-ray welding tests. In the experimental part, the procedure and results of testing butt weld joint are described by both non-destructive methods. The butt weld joint was made from steel S420MC. Each indication obtained by the ultrasonic and x-ray technique is supplemented by the macrostructure of the weld taken from the indication position. The results of the experimental work mentioned in the article point to the possibility and reliability of the identification of melting defects by selected nondestructive methods in terms of their character and orientation.

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Authors and Affiliations

R. Koňár
M. Mičian
M. Boháčik
M. Gucwa
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Abstract

The phenomenon of “soft zone” is occurring in the heat affected zone (HAZ) of high strength low alloy (HSLA) steels. Therefore, the process of weld metal solidification and phase transformation in HAZ is essential to understand the behaviour of the material, especially in the case where welded joints are debilitating part of the construction. The simulation program SYSWELD is powerful tool to predict solidification and phase transformation of welding joint, what correspond to the mechanical properties of the joints. To achieve relevant results of the simulation, it is necessary to use right mathematic-material model of the investigated material. Dilatometric test is the important methods to gather necessary input values for material database. In this paper is investigated physical and metallurgical properties of S960MC steel. The dilatometric curves were carried out on the laboratory machine dilatometer DIL 805L. In addition to determination of the phase transformation temperatures at eight levels of the cooling rate, the microstructure and hardness of the material are further analysed. The hardness of the samples reflects the achieved microstructure. Depending on the cooling rate, several austenitic transformation products were observed such as pearlite, bainite, martensite and many different ferritic microstructures. The differences between the transformation temperature results using the first derivation method and the three tangent method are up to 2%. The limit cooling rate was set at value 30°C/s. The microstructure consists only of bainite and martensite and the hardness reaches a value of 348HV and higher.
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Bibliography

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Authors and Affiliations

M. Málek
1
M. Mičian
1
ORCID: ORCID
J. Moravec
1

  1. Faculty of Mechanical Engineering, Technical University of Liberec, Studentská 1402/2, 461 17 Liberec I, Czech Republic
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Abstract

The application of hardfacing is one of the ways to restore the functional properties of worn elements. The possibility of using filler materials rich in chrome allows for better wear resistance than base materials used so far. The paper presents the results of research on the use of 3 different grades of covered electrodes for the regeneration of worn track staves. The content of the carbon in the covered electrodes was from 0,5% to 7% and the chromium from 5% to 33%. The microscopic and hardness tests revealed large differences in the structure and properties of the welds. The differences in the hardness of the welds between the materials used were up to 150 HV units. The difference in wear resistance, in the ASTM G65 test, between the best and worst materials was almost 12 times big.

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Authors and Affiliations

M. Gucwa
J. Winczek
P. Wieczorek
M. Mičian
ORCID: ORCID
R. Koňár
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Abstract

This research is focused on the analysis of heat-affected sub-zones in 2 mm thick steel S960MC samples, with the aim of observing and evaluating the mechanical properties after exposure to temperatures corresponding to individual heat-affected sub-zones. Test samples were prepared using a Gleeble 3500 thermo-mechanical simulator. The samples were heated in the range from 550°C to 1350°C and were subsequently quickly cooled. The specimens, together with the base material, were then subjected to tensile testing, impact testing, and micro-hardness measurements in the sample cross-section, as well as evaluation of their microstructure. Fracture surfaces are investigated in samples after impact testing. The heat-affected sub-zones studied indicate high sensitivity to the thermal input of welding. There is a significant decrease in tensile strength and yield strength at temperatures around 550°C.

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Authors and Affiliations

M. Mičian
ORCID: ORCID
J. Winczek
D. Harmaniak
R. Koňár
M. Gucwa
J. Moravec
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Abstract

The work is focused on welding of fine-grained ultra-high-strength steel S960MC by laser beam welding and electron beam welding technologies. For a given type of steel, when the heat input is exceeded, the mechanical properties of welded joints will deteriorate. As a result, using beam welding technologies to limit the amount of heat input is recommended. Several butt welds were made, and mechanical tests and macroscopic analyses were performed to determine the impact of welding parameters on mechanical properties. Using beam welding technologies, the value of heat input was reduced by up to 73% compared to gas metal arc welding. When compared to a gas metal arc welded joint, the width of the soft zone was reduced by 69 to 79%. This resulted in a considerable reduction in the width of the soft zone, which was reflected in a 24% increase in yield strength and a 23% increase in tensile strength compared to gas metal arc welding.
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Authors and Affiliations

M. Mičian
1
ORCID: ORCID
M. Frátrik
1
ORCID: ORCID
J. Bárta
2
ORCID: ORCID

  1. University of Žilina, Faculty of Mechanical Engineering, Univerzitná 8215/1, 010 26 Žilina, Slovak Republic
  2. Slovak University of Technology, Faculty of Materials Science and Technology in Trnava, J. Bottu 2781/25, 917 24 Trnava, Slovak Republic

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