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1

Weld joint properties of nitrogen-alloyed austenitic stainless steel using multi-pass GMA welding

Kumar Naveen, Arora Navneet, Goel S. K.

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 3

266--278

EN

The welding of nitrogen (0.29 wt%)-alloyed austenitic steel (grade 23-8-N) was performed with gas metal arc welding process. Solution treatment was performed at 950 °C and 1150 °C on base metal prior to weld. Base metal after second treatment has maximum ultimate tensile strength of 942 MPa and impact toughness 66 J. The microstructures of different zones of the weld joint were characterized using an optical microscope and field scanning electron microscope (FESEM). The microhardness, tensile and impact toughness tests of the weldments were conducted along with weld ferrite evaluation. ER2209 duplex filler metal used for welding has lower C and N content which changed the weld solidification mode. Weld has microstructure containing austenite + ferrite. Being a strong austenite former, nitrogen caused minimum ferrite near weld–HAZ interface while maximum ferrite content was observed at weld centre. Weld metal has minimum while base metal has maximum microhardness. UTS (892 MPa) and impact strength (96 J) of weld made on 1150 °C solution-treated base metal were maximum as compared to other weld joints.

2

Crack resistance of tool steels corresponding with the chemical composition of their matrices

Pacyna J.

Archives of Materials Science and Engineering

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2017

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Vol. 86, nr 1

5--14

EN

Purpose: of the presented investigations was showing that the crack resistance of tool steels depends on their hardenability and phase transformations occurring in the quenched matrix at tempering. The chemical composition of austenite decides on the steel hardenability while phase transformations after tempering can be influenced (apart from the chemical composition) by the heating method. Design/methodology/approach: of investigations was based on the analysis of dilatograms and the achieved aim was to obtain the hard tool steel (app. 500 HV30) for hot works. Samples of a diameter of 10 mm (without a notch) made of this steel were not broken by the Charpy impact test of energy of 30 kGm. Findings: of these investigations are practical. Grain boundaries of prior austenite should be protected against secondary precipitates, which constitute natural nuclei of diffusive structures. It is also possible to control phase transformations at tempering. Research limitations/implications: constitute the availability of the adequate equipment for investigating the kinetics of phase transformations of undercooled austenite and the kinetics of phase transformations after tempering. Practical implications: for the industry are such that the proposed tool steels of a high crack resistance contain molybdenum and nickel. Thus, these steels are very expensive. Originality/value: of these investigations was confirmed in the industrial practice.

3

Influence of Heat Treatment on Content of the Carbide Phases in the Microstructure of High-Speed Steel

Jaworski J., Kluz R., Trzepieciński T.

Archives of Foundry Engineering

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2017

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Vol. 17, iss. 3

59--62

EN

This article presents the results of investigations of the effect of heat treatment temperature on the content of the carbide phase of HS3-1-2 and HS6-5-2 low-alloy high-speed steel. Analysis of the phase composition of carbides is carried out using the diffraction method. It is determined that with increasing austenitising temperature, the intensification of dissolution of M6C carbide increases. As a result, an increase in the grain size of the austenite and the amount of retained austenite causes a significant reduction in the hardness of hardened steel HS3-1-2 to be observed. The results of diffraction investigations showed that M7C3 carbides containing mainly Cr and Fe carbides and M6C carbides containing mainly Mo and W carbides are dissolved during austenitisation. During austenitisation of HS3-1-2 steel, the silicon is transferred from the matrix to carbides, thus replacing carbide-forming elements. An increase in a degree of tempering leads to intensification of carbide separation and this process reduce the grindability of tested steels.

4

A study on the effect of different activating flux on A-TIG welding process of incoloy 800H

Sridhar S. P., Kumar S. A., Sathiya P.

Advances in Materials Science

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2016

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Vol. 16, nr 3(49)

26--37

EN

This study investigates the effect of different activating flux such as V2O5, TiO2, MoO3, Cr2O3, and Al2O3 on A-TIG welding process of Incoloy 800H. The influence of the flux on the depth of penetration and on mechanical and metallurgical characteristics of the weld were studied and compared with autogeneous TIG welds which were welded with the same process parameters and conditions. The use of TiO2 flux gave full depth of penetration and the use of V2O5, Cr2O3 flux gave increased penetration as compared to autogeneous TIG welds while the use of Al2O3 and MoO3 led to the detoriation of the effect.

5

The issue of using remelted CoCrMo alloys in dental prosthetics

Walczak M., Beer K., Surowska B., Borowicz J.

Archives of Civil and Mechanical Engineering

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2012

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Vol. 12, no. 2

171--177

EN

The most popular prosthetic restorations are skeletal dentures. Clinical failures in the case of these prostheses are associated primarily with the accuracy and precision of the design, and laboratory procedures such as: melting and casting technique as well as the quantity of the once remelted alloy used for the batch. This article analyzes the impact of the amount of recycled material on the mechanical properties and structure of dental alloy CoCrMo. Vacuum casting method has been applied and alloys remelted with output compositions of 0, 25, 50, 75 and 100% of fine material. The static tensile test, microstructural analysis and SEM observation as well as macrohardness test have been conducted. It was observed that the mechanical strength of all remelted alloys is worse than the strength of the fine alloy. A heterogeneity increase in the structure of alloys with more recycled material was noticeable. Moreover, the occurrence of precipitates of various types of carbides and the presence of intermetallic phases which have a determining effect on the mechanical properties of received castings were noted.

6

Influence of rolling conditions and aging process on mechanical properties of high manganese steels

Mazancova E., Ruziak I., Schindler I.

Archives of Civil and Mechanical Engineering

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2012

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Vol. 12, no. 2

142--147

EN

Three laboratory cast and rolled high manganese steels with different Mn (in the range of 24–28 wt%), C (in the interval of 0.2–1.2 wt%) and Al (from 2.3 wt% to 12 wt%) contents has been investigated. Differences in chemical compositions, rolling conditions and followed by aging process at the temperature of 500 °C and four different aging dwells (in the range of 6 min to 60 min) have led to various k-carbides precipitation. The k-carbides have been responsible for the mechanical properties. The intragranular type of nano-size has increased the strength, respectively hardness level whereas the k-carbides nucleated in the intergranular form have reached size of micrometre and in lower volume fraction have not been importantly able to increase the matrix hardness, especially in case of lower C portion. Balanced Mn, C and Al contents for optimised k-carbides precipitation have been also discussed. The materials were hot rolled to strips of 1.9 mm in thickness from the heating temperature of 1100 °C using the rolling mill Tandem.

7

The Cr3C2 thermal spray coating on Al-Si substrate

Richert M., Książek M., Leszczyńska-Madej B., Nejman I., Grzelka R., Pałka P.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 38, nr 1

95-102

EN

Purpose: The objective of this work was to present the changes between the plasma sprayed and high velocity oxy-fuel (HVOF) wear Cr3C2 resistant coats. The differences in microstructure and microhardness of coatings were investigated. The characterization of fully melted, un- melted and partly melted areas was performed. Design/methodology/approach: The investigated coats contained very differentiate areas, especially plasma sprayed layers. Systematic investigations of microstructure by using optical, electron scanning microscopy and transmission electron microscopy selected fully melted, un- melted or partly melted areas and their characteristic features were performed. Microhardness of coats was measured and compared with the similar literature results. Findings: Microstructure of plasma sprayed coats was finding as consisting from elongating splats, additionally contained un-melted previous particle of powder and some voids and oxides. Contrary to this the HFOV coatingss were more uniform containing almost equiaxial grains. The microhardness of HFOV coatings was almost two times higher than plasma sprayed ones. Practical implications: The performed investigations provide information, which could be useful in the industrial practice about the essential features of wear resistant plasma sprayed coatings. Originality/value: It was assumed that HVOF coatings have more uniform microstructure, higher microhardness, which could suggests better resistance before the wear and grindability.

8

Effect of deep cryogenic treatment on substructure of HS6-5-2 high speed steel

Jeleńkowski J., Ciski A., Babul T.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 43, nr 1

80-87

EN

Purpose: The purpose of this study was using of transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) in order to reveal the changes in substructure of speed steel made with deep cryogenic treatment (DCT), in comparison with substructure formed by conventional heat treatment for secondary hardness. Design/methodology/approach: The HS6-5-2 high speed steel was heat treated in a conventional mode for secondary hardness or was processed in a mode with use of DCT, with and without next tempering. Transmission electron microscopy and scanning electron microscopy observations were carried out. Studies of thermal stability in range of temperatures from -196 °C to 400 °C were performed using differential scanning calorimetry (DSC). Findings: Observations made with aid of SEM-TEM microscope revealed the presence of high density of globular clusters situated at dislocations, and precipitations of the fine carbide plates, located in twinned crystals of martensite. Thermal analysis (DSC) showed an occurrence of higher exothermic effects in specimens treated with use of DCT, than in specimens heat treated conventionally. In steel samples after quenching and DCT the additional exothermic effect was observed. Electron diffraction in TEM studies of these specimens allowed to observe reflections of which indexing exhibited that the precipitated carbide phase has crystallographic structure of B1 type. Research limitations/implications: Extremely high dispersion of carbide phases and a high state of stress that accompanies the stage of precipitation, make difficult the identification of the lattice structure of precipitations, its crystallographic relationships and the degree of coherence with the matrix. Identification of the type of carbides (ĺ, ç, B1, and others) and their coherence with matrix become time-consuming. This important issue requires detailed studies using high-resolution microscopes. Conditions of the early stage of the precipitation process affect the stability of induced strengthening and service-life of tools. Practical implications: Research of HS6-5-2 high speed steel allowed concluding that DCT, besides refinement of martensite grain size, causes an increase of quantity of sites for nucleation of clusters, in which during tempering the B1 carbides are formed. These fine, coherent with matrix and stable carbides are found to be responsible for enhancement of toughness and wear resistance of HSS tools. Originality/value: The issue of DCT is a niche topic in Poland, there are no detailed studies on the changes taking place during this process.

9

Formowanie się napoin na bazie niklu umacnianych węglikami metali przejściowych

Bober M., Senkara J.

Biuletyn Instytutu Spawalnictwa w Gliwicach

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2010

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R. 54, nr 5

103-107

PL

Przedmiotem badań było otrzymywanie metodą plazmową napoin na osnowie stopu NiSi2B z dodatkami węglików metali IVB i VIB grupy układu okresowego na podłożu ze stali niskostopowej S355J0. Analiza oddziaływań międzyfazowych oraz struktury napoin wykazała, iż odmienny charakter oddziaływania węglików metali obu grup z ciekłym stopem niklu wpływa na rozmieszczenie i udział cząstek fazy umacniającej w matrycy. Wykazano, iż rozmieszczenie twardych cząstek, zbliżone do równomiernego, ma miejsce w powłokach umacnianych węglikami metali grupy VIB układu okresowego pierwiastków. Objętościowy udział węglików tytanu i cyrkonu zwiększa się wraz ze wzrostem natężenia prądu, natomiast w powłokach zawierających węgliki chromu, molibdenu i wolframu ich udział maleje, co związane jest z odmiennym mechanizmem oddziaływania z ciekłą osnową.

EN

The object of the investigations was to obtain NiSi2B based weld overlays with additions of carbides of the metals from IVB and VIB group of the Mendeleev's table over the S355JO low alloy steel base by plasma (PPTAW) method. The analysis of interfacial reactions and overlays structure has shown that the different character of reaction of both group metal carbides with liquid nickel alloy influences the lay-out and concentration of strengthening phase particles in the base. It has been shown also that the almost uniform lay-out of hard particles occurs in overlays strengthened with carbides of metals from VIB group of the periodic system. The volume fraction of TiC and ZrC grows larger with the increase in welding current, whereas in overlays strengthened with chromium, molybdenum and tungsten carbides the fraction of strengthening phase grows smaller what is connected with the different mechanism of reaction with liquid matrix.

10

Microstructural characterization of the new tool Ni-based alloy with high carbon and chromium content

Bała P.

Archives of Metallurgy and Materials

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2010

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Vol. 55, iss. 4

1053-1059

EN

The concept of new tool materials, based on Ni alloys strengthened by intermetallic compounds, intended for applications at high temperatures is presented in the paper. The chemical composition of this new material was designed in such a way as to obtain the matrix strengthening by means of the precipitation of intermetallic compounds rich in Ni and to have the carbide fraction above 25%. Carbides should remain stable in the microstructure, regardless of the heat treatment, since they favourably influence an abrasion resistance. The results of microstructure investigations in the as-cast condition, are given. The type of phases appearing in the microstructure was determined and their morphology described. The main microstructure components of the investigated Ni-based alloy with high carbon and chromium content are: the γ phase, which constitutes a matrix, the γ' phase, which occurs as fine globular precipitates and the primary Ta and Cr carbides (of MC and M7C3 type - respectively).

PL

W pracy przedstawiono koncepcję nowych materiałów narzędziowych na osnowie niklu umacnianych związkami faz międzymetalicznych, przewidywanych do pracy w wysokich temperaturach. Skład chemiczny nowego materiału zaprojektowano tak, aby umocnienie osnowy uzyskać w wyniku wydzielania związków metalicznych bogatych Ni, a udział węglików wynosił ponad 25%. Węgliki powinny pozostać stabilne w mikrostrukturze niezależnie od obróbki cieplnej, wpływając korzystnie na odporność na ścieranie. Zamieszczono badania mikrostruktury stopu wstanie lanym. Określono rodzaj faz występujących w mikrostrukturze oraz opisano ich morfologię. Głównymi składnikami mikrostruktury badanego stopu na osnowie Ni, o dużej zawartości węgla i chromu są: faza γ, która stanowi osnowę, faza γ', która występuje w postaci drobnych kulistych wydzieleń oraz pierwotne węgliki Ta (typu MC) i Cr (M7C3).

11

New tool materials based on Ni alloys strengthened by intermetallic compounds with a high carbon content

Bała P.

Archives of Materials Science and Engineering

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2010

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Vol. 42, nr 1

5-12

EN

Purpose: The concept of new tool materials, based on Ni alloys strengthened by intermetallic compounds, intended for operations in high temperatures is presented in the hereby paper. The proposed chemical composition and the results of microstructure investigations as well as hardness testing in as-cast condition - are given. Design/methodology/approach: A test melt of a mass of approximately 1 kg was done in a vacuum furnace, and cast into a ceramic mould. The microstructure of the investigated material was examined by a light microscope Axiovert 200 MAT and the scanning electron microscope FIB Zeiss NEON 40EsB CrossBeam. Dilatometric experiment was performed by means of the Adamel Lhomargy DT 1000 dilatometer . Findings: The main components of the microstructure of the nickel-base investigated alloy are: the ? phase, which constitutes the matrix and the ?' phase. This ?' phase occurs as fine globular precipitates as well as in a form of primary Ta carbides of MC type. Primary carbides of irregular shapes are uniformly distributed not forming agglomerates. The assumed volume fraction of the primary carbides was achieved. Research limitations/implications: Identification of microstructure components on Ni-based materials strengthened by particles of intermetallic phases of a high carbon content. Practical implications: New tool material for hot-working. Originality/value: The new chemical compositions of tool materials based on Ni alloys strengthened by intermetallic compounds with high carbon content.

12

Influence of solution heat treatment on the microstructure and hardness of the new Ni-based alloy with a high carbon content

Bała P.

Archives of Materials Science and Engineering

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2010

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Vol. 45, nr 1

40-47

EN

Purpose: The main purpose of the hereby paper was the determination of the temperature and time of solution heat treatment influence on a microstructure and hardness of the newly designed model alloy, being the model Ni-based tool material - intended for operations at high temperatures - strengthened by compositions of intermetallic phases, of a high carbon and cobalt content. Design/methodology/approach: A test melt of a mass of approximately 1 kg was done in a vacuum furnace, and cast into a ceramic mould. The microstructure of the investigated material was examined by means of the light microscope Axiovert 200 MAT and the scanning electron microscope FIB Zeiss NEON 40EsB CrossBeam. Samples for investigations were solution heat treated from the temperature range: 1020-1170°C. After heating to the desired temperature they were hold at this temperature for 0.5 or for 2 hours and then water-cooled. The volume fraction of primary tantalum carbides and graphite was estimated by the point-count method. Approximately 30 measurements were performed for each variant of the heat treatment. Findings: The main constituents of the microstructure of the nickel-base investigated alloy in as-cast state are: the γ phase, which constitutes the matrix, the γ' phase (γ' phase occurs as fine globular precipitates) as well as primary Ta carbides of MC type. Primary carbides of irregular shapes are uniformly distributed not forming agglomerates. Solution heat treatment of the investigated alloy from higher and higher temperatures causes a slow increase of a graphite fraction, nevertheless an application of a temperature of 1170°C significantly increases its fraction. Research limitations/implications: The investigated alloy is the model alloy. Taking into account its chemical composition the possibility of improving its properties by means of the heat treatment should not be expected. In the first place the fraction of carbide forming elements should be increased to eliminate graphite, and secondly the fraction of elements forming γ' phase should be increased to obtain the possibility of the modification of properties by means of solution heat treatment and aging. Nonetheless the achieved results will be utilised at the chemical composition modification of Ni-based alloys of a high carbon content. Practical implications: Broadening the knowledge on the carbides stability in Ni-based alloys, which will help in designing new Ni-based alloys of a high carbon content. Originality/value: Determination of the stability of primary carbides at high temperatures in Ni-based alloys of a high carbon and cobalt content.

13

Bainite obtaining in cast iron with carbides castings

Pietrowski S., Gumienny G.

Archives of Foundry Engineering

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2010

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Vol. 10, iss. 1

109-114

EN

In these paper the possibility of upper and lower bainite obtaining in cast iron with carbides castings are presented. Conditions, when in cast iron with carbides castings during continuous free air cooling austenite transformation to upper bainite or its mixture with lower bainte proceeds, have been given. A mechanism of this transformation has been given, Si, Ni, Mn and Mo distribution in the eutectic cell has been tested and hardness of tested castings has been determined.

14

Laser surface treatment of the hot work tool steel alloyed with TaC and VC carbide powders

Dobrzański L. A., Jonda E., Klimpel A.

Archives of Materials Science and Engineering

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2009

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Vol. 37, nr 1

53-60

EN

Purpose: The paper presents investigation results of the structure and properties of alloying surface layer of the X40CrMoV5-1 hot work tool steel, using the high power diode laser HPDL. Tantalum and vanadium carbides powders were used for alloying and the X40CrMoV5-1 conventionally heat treated steel was used as reference material. Design/methodology/approach: Metallographic examinations of the material structures after laser alloying surface layer were made on light microscope and transmission electron microscope. The resistance research has been done with the use of the pin-on-disc method. Hardness tests were made with Rockwell method in C scale. Findings: It was found out in examinations of the surface layer that it can be possible to obtain high quality top layer with better properties compared to material after a standard heat treatment. Research limitations/implications: In this research two powders (TaC and VC) were used for alloying of the surface layer of investigated steel. Practical implications: The structure as well as improvement of mechanical properties is a practical aim of this work as well as improvement of hardness as a very important properties for practical use. Originality/value: The research results of this type of heat treatment show that there is a possibility of applying the worked out technology to manufacturing or regeneration of chosen hot working tools.

15

Precipitation of carbides in Cr - Mo - V cast steel after service and regenerative heat treatment

Golański G., Wieczorek P.

Archives of Foundry Engineering

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2009

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Vol. 9, iss. 1

97-102

EN

The paper presents results of research on precipitation processes in chromium - molybdenum - vanadium cast steel. The examined material was the following cast steel grade: L21HMF and G17CrMoV5 - 10 (L17HMF) after long-term operation at elevated temperatures and after regenerative heat treatment. Identification of precipitates was performed by means of the transmission electron microscope using carbon extraction replicas and thin foils. On the basis of identifications it has been proved that in the structure of investigated cast steel grades, degraded by long-term operation, there are a few sorts of carbides with diverse stability, such as: M3C; M2C, M23C6, MC, M7C3. Moreover, the occurrence of compound complexes of precipitates - the so called 'H-carbides' - has been revealed. Heat treatment of the examined cast steels contributed to changes in morphology and precipitation type. Whilst in the bainitic structure, obtained through heat treatment, only the occurrence of carbide types, such as: M3C; M23C6 and MC has been noticed.

16

Phase transformations and microstructure of IN-713C nickel superalloy

Binczyk F., Śleziona J.

Archives of Foundry Engineering

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2009

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Vol. 9, iss. 2

109-112

EN

The study presents the results of investigations of phase transformations taking place during melting and solidification and of microstructural examinations carried out on the family of IN 713C nickel superalloys. Examinations were carried out by the method of thermal analysis (ATD) and differential scanning calorimetry (DSC). It has been concluded that the method of thermal analysis (ATD) enables more precise assessment of the precipitation of the primary phases of a low value of the solidification enthalpy. The advantage of DSC is the possibility of determination of the value of the heat (enthalpy) of phase transformations during alloy melting and solidification. The measured parameters of Tlik and Tsol are comparable for both methods. Microstructural examinations have confirmed the phenomena accompanying phase transformations, i.e. the precipitation of primary carbides, the solidification of [...] phase matrix and carbide eutectic, and the formation of [...] phase in solid state.

17

Effect of gas corrosion on the character of phase boundaries in Ni3Al / WC composite

Fraś E., Janas A., Kolbus A., Olejnik E.

Archives of Foundry Engineering

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2009

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Vol. 9, iss. 2

87-92

EN

In view of quite specific physico-chemical and performance properties, the composite based on an intermetallic Ni3Al compound reinforced with tungsten carbides (WC) was selected for investigations. The said composite is characterised by very good mechanical and tribological properties within a wide range of temperatures, combined with good corrosion resistance. In fabrication of the Ni3Al/WC composite, a modified variant of the SHS process was applied. It is the SHSB process, i.e. the Self-Propagating High-Temperature Synthesis in Bath. The said method enables obtaining pure products of reaction, unoxidised and free from the precipitates of alien phases. The main goal of this study has been determination of the susceptibility of the Ni3Al/WC composite to gas corrosion. To examine the microstructure and chemical composition of both the composite and the scale, the metallographic and structural examinations were made, using optical and scanning microscopy.

18

Cast in situ composites of Ni3Al / MeC type

Fraś E., Janas A., Kolbus A., Olejnik E.

Archives of Foundry Engineering

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2009

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Vol. 9, iss. 2

81-86

EN

In this work a new method SHSB (Self- Propagating High-Temperature Synthesis in Bath) has been used to produce of five new composites i.e.Ni3Al / TiC, Ni3Al / WC, Ni3Al / Zr, Ni3Al / NbC and Ni3Al /TaC (in the amount of carbides of 5% volume fraction.) The composites fabricated by the 'in situ' process, with the Ni3Al compound used as a matrix material and the reinforcement composed of Ti, W, Zr, Nb or Ta carbide particles were made. Fabrication of composites was carried out in Balzers vacuum furnace and conducted the process in the atmosphere of argon at a negative gas pressure of 0,5 MPa. After melting down of aluminium and completion of the exothermic reaction between mixing powder of carbon, aluminium, titanium or tungsten, zirconium, niobium and tantalum, boron in the form of Al-B 3% master alloy was introduced to alloy melt. From thus fabricated composites, the specimens were prepared for metallographic examinations, and scanning topographic analysis. It have been shown that the size of TiC and TaC particles was comprised in a range of up to 10 [...]. The NbC and ZrC carbides were characterised by the dimensions of up to 20 [...], while WC carbides were the largest (up to 80 [...].) In all the examined composites, the X-ray microanalysis revealed total absence of reaction products at the matrix reinforcing particle interface. The SHSB process eliminated the fundamental problem - reactivity of the matrix-particle system, observed in the ex situ methods .

19

Bainitic nodular cast iron with carbides obtaining with use of Inmold method

Gumienny G.

Archives of Foundry Engineering

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2009

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Vol. 9, iss. 3

243-248

EN

In these paper bainitic nodular cast iron with carbides as-cast obtaining has been presented. This cast iron has been obtained with use of Inmold method. It was shown, that there is the possibility of bainite and carbides obtaining in cast iron with Mo and Ni for studied chemical composition.

20

The influence of pre-tempering on the mechanical properties of HS6-5-2 high speed steel

Bała P., Pacyna J.

Archives of Metallurgy and Materials

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2008

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Vol. 53, iss. 3

795-801

EN

Main objective of the research presented in this work was the evaluation of an influence of pre-tempering on the properties of HS6-5-2 steel after principal tempering. It was shown, that advance (by pre-tempering) of selected phase transformations during tempering may affect steel properties after principal tempering. Samples of test steel, previously ąuenched in oil from the temperaturę of 1240°C have been pre-tempered at 20, 250, 450 and 550°C for 1.5 hour and subsequently cooled in air. Then principal tempering has been applied 3x580°C/lh. Due to high brittleness of test steel it was decided to test their strength with static bend test. The tests have been carried out on 05 samples using an INSTRON testing machinę. Evaluation of crack resistance of test steels has been madę by means of linear elastic fracture mechanics method on the basis of the measurement of stress intensity factor KIc. It has been found that, in test steel in which remains a lot of retained austenite after hardening, the pre-tempering within the rangę of cementite precipitation and transformation of retained austenite, adversely affects the properties after principal tempering. Pre-tempering of the investigated steel at the temperaturę insignificantly higher than precipitation of MC - type alloy carbides start temperaturę results in decrease in strength properties at insigniticant increase of KIc.

PL

W pracy przedstawiono wpływ wstępnego odpuszczania na własności stali HS6-5-2 po odpuszczaniu zasadniczym. Próbki badanej stali, uprzednio zahartowane od temperatury 1240°C (chłodzenie w oleju), odpuszczano wstępnie przy 20, 250, 450 i 550°C przez czas 1,5 godziny po czym chłodzono na powietrzu. Następnie zastosowano odpuszczanie zasadnicze 3x580°C/lh. Ze względu na to, iż badaniom podlegała stal szybkotnąca, zdecydowano się na badania wytrzymałości w statycznej próbie zginania. Badania wykonano przy użyciu maszyny wytrzymałościowej INSTRON na próbkach 5. Ocenę odporności na pękanie badanych stali wykonano metodą liniowo-sprężystej mechaniki pękania w oparciu o pomiary współczynnika intensywności naprężeń KIc. Próbki zginano trójpunktowo na maszynie wytrzymałościowej INSTRON. Stwierdzono, iż odpuszczanie wstępne w zakresie wydzielania cementytu i przemiany austenitu szczątkowego wpływa niekorzystnie na własności po odpuszczaniu zasadniczym. Wstępne odpuszczanie badanej stali przy temperaturze nieznacznie wyższej od temperatury początku wydzielania węglików stopowych typu MC powoduje spadek własności wytrzymałościowych przy nieznacznym wzroście KIc.