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Research and Development of the Solidification of Slab Ingots from Special Tool Steels

Tkadlečková M., Michalek K., Gryc K., Socha L., Jonšta P., Saternus M., Pieprzyca J., Merder T.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 3

1453--1458

EN

The paper describes the research and development of casting and solidification of slab ingots from special tool steels by means of numerical modelling using the finite element method. The pre-processing, processing and post-processing phases of numerical modelling are outlined. Also, problems with determining the thermophysical properties of materials and heat transfer between the individual parts of the casting system are discussed. Based on the type of grade of tool steel, the risk of final porosity is predicted. The results allowed to improve the production technology of slab ingots, and also to verify the ratio, the chamfer and the external/ internal shape of the wall of the new designed slab ingots.

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Hydrogen Embrittlement of Welded Joint Made of Supermartensitic Stainless Steel in Environment Containing Sulfane

Jonšta P., Váňová P., Brožová S., Pustějovská P., Sojka J., Jonšta Z., Ingaldi M.

Archives of Metallurgy and Materials

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2016

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Vol. 61, iss. 2A

709--712

EN

The work is focused on evaluation of resistance of the welded joint made of supermartensitic 13Cr6Ni2.5Mo stainless steel to sulfide stress cracking. Testing method A and solution B in accordance with NACE TM 0177 were used. All the testing samples were ruptured in a very short time interval but welded joint samples were fractured primarily in the weld metal or in heat affected zone and not in the basic material. Material analysis of samples were made with use of a ZEISS NEOPHOT 32 light microscope and a JEOL 6490LV scanning electron microscope.

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Sulfidické praskání pod napětím svarového spoje supermartenzitické oceli 13Cr6Ni2,5Mo

Jonšta P., Sojka J., Váňová P.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2008

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z. 92

45-46

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Structural analysis of parts of personal computer hard disks

Malcharcziková J., Váňová P., Jonšta P.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2008

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z. 92

51-52

EN

Personal computers including all its parts, CPU, monitor, keyboard and mouse belong to the group of "information technology and telecommunication equipment". At the present consumption rate personal computers are scrapped when they are fully or partly operating, but they do not satisfy their owners in their parameters. Operating parts, such as hard disks from personal computers, can be further used, e. g. as backup sources or by less demanding users. If it does not happen, electric and electronic waste is produced. According to the Waste Disposal Association it is necessary to support the use of waste in order to eliminate the amount of wastes determined for disposal and to preserve natural resources, particularly by reuse, recycling, composting and use of energy from wastes. Selected parts of waste hard disks from personal computers were evaluated metallographically. In addition, the used coatings were characterized and their thickness was determined. As it was found out, basic parts of hard disks are produced from basic metals, such as iron, aluminium and copper. The contents of the contribution should add to increasing knowledge and the possibilities of electrical waste recycling.

5

Options for material usage from discarded mobile telephones

Váňová P., Malcharcziková J., Jonšta P.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2008

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z. 92

63-64

EN

Mobile telephones belong to the fastest updated electronic devices, which generates thousands of tons of waste every year. According to the research by the Nokia company, only very few mobile telephones are recycled after their expiration date, whereas 80 % of Nokia devices are recyclable and contain valuable sorts of material. It is exactly this type of electronic waste that can provide us with various usable material sorts including metals such as copper, iron, nickel, silver and gold. A mobile telephone contains approx. 15-18 % of copper and 3 - 8 % of iron. A significant part of a mobile telephone is composed from miscellaneous types of plastics which are easy to recycle after sorting. Out-of-use mobile telephones belong to the waste group of electrical and electronic devices. Therefore, with respect to the environment, it is necessary to pay an intensive attention to the issue of collecting and recycling this type of devices, since any mobile phone which is not used any more constitutes an environmental burden or the resource of valuable raw materials. This thesis includes a material analysis of selected mobile telephones.

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Hydrogen diffusion in micro alloy steels

Sojka J., Jonšta P., Rytířová L., Jerome M., Zajac J., Sozanska M.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2007

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Vol. 321, z. 89

121-122

EN

Petroleum and natural gas systems can be contaminated with wet H2S. This environment is very aggressive to the steels used in the transport and processing of these products and it can result in various forms of hydrogen embrittlement. The reaction between wet H2S and the steel generates atomic hydrogen, which can be, at least partially, absorbed into the steel. In the absence of applied stress, the diffused hydrogen can cause hydrogen induced cracking (HIC). The resistance of steels to HIC is closely related to the microstructure features: nonmetallic inclusions, hard phase constituents, banded structures etc. In the presence of applied or residual stress, the failure process can occur by sulphide stress cracking (SSC) or stress oriented hydrogen induced cracking (SOHIC). In the case of SSC, steel resistance is commonly derived from its strength level. It is generally accepted that steels having tensile strength less than 690 MPa approx. are resistant to SSC. The role of microstructure is not emphasized although there are some works showing that microstructure can also play an important role in the case of SSC. In the previous works, it was proved that even in case of SSC the resistance of the steels can be improved by the heat treatment – quenching and tempering, if the banded structure of ferrite and pearlite is replaced by the tempered martensite and/or bainite. The resistance of the steel to the hydrogen embrittlement is affected by both the microstructure and hydrogen concentration. To understand the hydrogen embrittlement it is necessary to characterize also the hydrogen transport – diffusion. In this work hydrogen diffusion coefficient in micro alloy X52 and X60 API steels (tubes), having different microstructures - banded ferrite and pearlite after hot rolling and the mixture of tempered bainite and martensite after quenching and tempering, are evaluated. The role of specimen orientation is also taken into account.

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Nickel super alloy INCONEL 713LC - structural characteristics after heat treatment

Jonšta P., Jonšta Z., Sojka J., Čižek L., Hernas A.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 22, nr 2

7-14

EN

Purpose: Nickel super alloy's products are mainly using for construction parts of jet engines, gas turbines and turbo-blowers. Design/methodology/approach: Super alloy was commercially produced and was investigated by using the light microscopy (OLYMPUS IX 71) and local chemical microanalysis and by the scanning electron microscopy (JEOL JSM 50A). Findings: we found a mode of optimum heat treatment. On the basis of obtained results it is possible to recommend a following regime of heat treatment: heating and dwell at the temperature exceeding 1240 degrees centigrade (min. 1260 degrees centigrade), so that precipitates at the grain boundaries dissolve completely, with subsequent slow cooling down to the temperature of approx. 940-950 degrees centigrade, so that there occurs intensive intra-granular precipitation of intermetallic phase gamma'. Research limitations/implications: The experiment was limited by occurrence a void in cast alloys. Practical implications: Nickel super alloy's products are mainly using for construction parts of jet engines, gas turbines and turbo-blowers. Originality/value: Mode of optimum heat treatment was proposed. On the basis of obtained results it is possible to recommend the most suitable heat treatment, which produce intensive intra-granular precipitation of intermetallic phase gamma'. It was received a new konw-how in this field.

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Slow strain rate test of the carbon steel of type A333 Gr. 6

Váňová P., Sojka J., Jonšta P., Kubečka P.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2006

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z. 88

121-125

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Sulphide Stress Cracking of API Carbon Steels

Sojka J., Jonšta P., Váňová P., Sozańska M.

Machine Dynamics Problems

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2004

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Vol. 28, No. 4

121-126

EN

In this paper results of SSC resistance of the same carbon steels are summarized. Several grades of steels have been tested, conforming to API grades X52 and X70 (API 5L Specification). Steels were tested in an as-received state or after laboratory heat treatments including quenching and termpering. Results showed that the resistance of steels to SSC depends strongly on their microstructure. Heats containing bands of non-tempered martensite or bainite exhibited rather poor resistance to SSC and failed and stresses well below the yield strength when tested according to the NACE TM 0177, Method A. It must be pointed out that hardness of all studied steels was well bellow the limit of 22 HRC. Tempering or quenching had a beneficial effect on resistance of steels to SSC despite the fact that mechanical properties (and hardness) increased. All the results indicate that microstructure plays important role also in the case of SSC. If this fact is not respected, a material non resistant to SSC can be chosen.