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1

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.

2

Influence of niobium on the structure and properties of the matrix of high-speed steel with nickel

Pacyna J., Dziurka R., Grudzień M.

Inżynieria Materiałowa

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2016

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Vol. 37, nr 6

335--340

EN

The following paper investigates two model alloys simulating the quenched matrix of high-speed steels with an addition of 1.5% Ni, which was enriched with 1% and 2% of Nb to increase abrasion resistance. Based on the alloys’ composition comprising of W, Mo, V and Cr, the simulations of the quenched matrix of the high-speed steels indicate sufficiently high hardenability. The purpose of increasing the nickel content in the composition of such alloys was to increase their crack resistance, whereas the addition of the strongly carbide-forming niobium in amounts of 1% and 2%, balanced by an additional carbon content, was aimed at increasing the abrasion resistance of these steels. The authors of the above mentioned chemical composition concept expect that these types of alloys will be used in the production of tools (rolls) designed for the rolling of metallurgical products which are difficult to produce (flat bars, channel bars and tee bars). The quenching temperature of both alloys was optimised on the base of the so called quenching series. The accurate CCT diagrams and the tempering series for revealing the secondary hardness effect were also performed for these alloys. All investigation stages were accurately documented by metallographic tests.

PL

W pracy postanowiono wznowić badania na osnowie zahartowanej stali szybkotnącej, jednakże jej skład uzupełniono dodatkiem około 1,5% Ni oraz dodatkami odpowiednio około 1% i 2% Nb. Dodatki niobu, jeżeli tylko zostaną zbilansowane odpowiednimi dodatkami węgla, powinny dzięki utworzeniu stabilnych węglików Nb4C3 zwiększyć odporność na ścieranie stopu, a dodatki niklu powinny zwiększyć jego odporność na pękanie. Takie postępowanie powinno umożliwić uzyskanie materiału narzędziowego odpornego na ścieranie oraz odpornego na pękanie o właściwościach zahartowanej osnowy stali szybkotnących. Autorzy składu chemicznego nowych stopów i ich koncepcji spodziewają się, że będą one stosowane do wytwarzania narzędzi (walców) przeznaczonych do walcowania produktów hutniczych, które są trudne do wytworzenia (płaskowników, ceowników oraz teowników).

3

Phase transformations in the precipitation hardened cast steel

Pacyna J., Dziurka R., Grudzień M.

Archives of Materials Science and Engineering

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2015

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Vol. 73, nr 2

62--68

EN

Purpose: The microstructure of the new ledeburitic, tool cast steel of the precipitation hardened matrix was designed. The concept of this microstructure was based on the microstructure of the steel-bonded carbides [1,2], in which a skeleton is built of sintered carbides. This skeleton is produced by the powder metallurgy methods and then filled with melted steel of the selected chemical composition. Design/methodology/approach: The new cast steel of the structure analogous to the steel-bonded carbides was conventionally melted in a furnace, however with omitting pressing and sintering operations of the powder metallurgy. The carbides skeleton in the new cast steel is formed by carbides of the MC type forming jointly ledeburite and its matrix constitutes steel hardened by precipitates of intermetallic compounds. This new material will be destined for tools of a moderate hardness (approximately 40 HRC), high abrasion resistance and high strength. Findings: Utilising hard carbides forming by elements of VB group of the Mendeleev’s table it is possible to design the tool material similar to the steel-bonded carbide of the selected matrix composition and primary carbides of MC type. Research limitations/implications: The chemical composition the matrix of designed material decides on its hardness and strength, the MC type carbides decide on the abrasion resistance and if they occur in the eutectic form they decide on a rather low fracture toughness. Therefore efforts should be undertaken to have non-ledeburitic materials. Practical implications: As a result of these investigations a new precipitation hardened cast steel have been worked out and a possibility of its industry applied was shown. Originality/value: The results of investigations of phase transformations in the new cast steel at its heating and cooling from the austenite range, are presented in the hereby paper.

4

Effect of heating rate on the phase transformations during tempering of low carbon Cr-Mn-Mo alloy steel

Dziurka R., Pacyna J., Tokarski T.

Archives of Materials Science and Engineering

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2013

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Vol. 63, nr 1

13--18

EN

Purpose: The effect of heating rate to the tempering temperature on the microstructure and properties of lath martensite tempered at a various temperatures was studied in literature from point of the cemntite precipitations view. It has been shown that cementite dispersion is finer and more uniform in the rapidly heated and tempered than in the slowly heated and tempered specimen. Aim of this work is to investigate the effect of heating rate on the phase transformations during tempering. Design/methodology/approach: The investigations of phase transformations during tempering of the low carbon steel were made on the grounds of dilatometric curves recorded during heating from as-quenched state. Heating to isothermal holding at 350°C was made with two different heating rates (100°C/s and 5°C/s) and was performed by use of the L78 R.I.T.A. dilatometer made by Linseis. The investigations of phase transformations during continuous heating from as-quenched state were performed by use of the DT 1000 dilatometer made by Adamel. Findings: It is possible to reduce probability of the occurrence of some phase transformations in favor of other. The difference in advancement of the various phase transformations can effects on various mechanical properties of the steels. Research limitations/implications: The effect of the heating rates (100°C/s and 5°C/s) during heating from as-quenched state on the phase transformations during isothermal holding at 350°C was submitted. It is expected to carry out further research on the effect of the heating rate on the phase transformations during isothermal holding at different temperatures and their effects on mechanical properties. Practical implications: The obtained information may be used to design new technologies of steels tempering. Originality/value: The new point of view on the tempering of the steels can be assumed.

5

Dilatometric investigations of phase transformations at heating and cooling of hardened, unalloyed, high-carbon steels

Pacyna J.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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Vol. 46, nr 1

7--17

EN

Purpose: The reason for writing this paper was to describe the kinetics of phase transformations during continuous heating from hardened state and subsequent cooling of unalloyed high carbon steel. Design/methodology/approach: Dilatometric investigations were performed using a DT 1000 dilatometer of a French company Adamel. Samples after quenching and quenching and sub-quenching in liquid nitrogen (-196 °C) were heated up 700 °C at the rate of 0.05 °C/s and subsequent cooled to room temperature at the rate of 0.05 °C/s. Findings: Regardless of heating the hardened high-carbon steel to 700 °C, a small fraction of the retained austenite remained in its structure, and was changing into fresh martensite only during cooling in the temperature range: 280°C-170°C. Research limitations/implications: Schematic presentation of the differential curve of tempering of the hardened high-carbon, unalloyed steel illustrating the phase transformations occurring during heating from hardened state. Practical implications: An observation, that a small fraction of the retained austenite remained in the structure of tempered high-carbon steel, indicates that even unalloyed steel should be tempered two times. Originality/value: Detailed descriptions of kinetics phase transformations during heating from hardened state of unalloyed high carbon steel.

6

Analiza temperatur krytycznych oraz zmian twardości i mikrostruktury stopu Ti6Al4V przy chłodzeniu z zakresu dwufazowego alfa+Beta i jednofazowego Beta

Dąbrowski R.

Rudy i Metale Nieżelazne

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2010

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R. 55, nr 10

708-716

PL

W artykule metodami dylatometryczną i metalograficzną określono temperatury początku i końca przemiany fazowej alfa + Beta - Beta przy nagrzewaniu stopu Ti6Al4V ze stanu wyżarzonego. Dokonano również analizy zmian zachodzących w jego mikrostrukturze przy chłodzeniu z zakresu dwufazowego alfa + Beta i jednofazowego Beta. W mikrostrukturze stopu oziębianego w wodzie od temperatury powyżej 970 stopni Celsjusza (z zakresu jednofazowego Beta) obserwuje się drobne, iglaste wydzielenia fazy martenzytycznej (prawdopodobnie alfa') oraz znaczny rozrost ziaren byłej fazy Beta. Uzyskane wyniki badań wstępnych stopu Ti6Al4V stanowią podstawę do interpretacji przemian fazowych zachodzących podczas jego odpuszczania. Kinetykę przemian fazowych przy odpuszczaniu zamierza się bowiem badać w przyszłości za pomocą oryginalnych wykresów CTPc stopni (czas--temperatura-przemiana przy nagrzewaniu ciągłym ze stanu zahartowanego), wprowadzonych już do literatury światowej, ale tylko dla stopów na osnowie żelaza.

EN

This paper presents the critical temperatures of alpha + Beta - Beta phase transformation during heating in previously annealed Ti6Al4V alloy which have been evaluated both by dilatometric and metallographic methods. Also, changes in alloy's microstructure taking place during cooling down from two-phase (alpha + Beta) and one phase (Beta) ranges have been analysed. In the microstructure of the alloy cooled down from temperature higher then 970 degrees of Celsius (one-phase range) in water, the very fine, needle-like precipitates (alpha' probably) are observed as well as unnormal grain growth of former Beta phase. Obtained results of this initial research can be used for the interpretation of phase transformation occurred in Ti6Al4V alloy during tempering. In future, the kinetics of the phase transformation during tempering will be investigated by original CHT (Continuous--Heating-Transformation) charts, which are already known and applied for iron-base alloys only.

7

Wyznaczanie temperatur początku przemian zachodzących podczas spiekania konstrukcyjnych stali manganowo-chromowo-molibdenowych

Sułowski M.

Rudy i Metale Nieżelazne

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2009

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R. 54, nr 7

422-435

PL

Celem badań było określenie temperatur początku przemian zachodzących podczas spiekania konstrukcyjnych stali zawierających 3 % Mn, 1,5 % lub 3 % Cr, 0,5 % lub 0,2 % Mo oraz 0,3 % C. Do badań wykorzystano komercyjne proszki stopowe Astaloy CrL i Astaloy CrM, proszek niskowęglowego żelazomanganu oraz proszek grafitu C-UF. Z proszków wyjściowych w mieszalniku Turbula w czasie 30 minut sporządzono mieszanki proszków, a następnie, metodą prasowania w sztywnej matrycy, sprasowano kształtki prostopadłościenne, o wymiarach 5 × 5 × 15 mm, przeznaczone do badań dylatometrycznych w dylatometrze poziomym Netzsch 402E. Wykonane badania dylatometryczne pozwoliły na określenie temperatur początku przemian perlitycznej, bainitycznej oraz martenzytycznej, mieszczących się odpowiednio w zakresie temperatur 600-650 stopni Celsjusza, 450-500 stopni Celsjusza oraz 200-300 stopni Celsjusza. Przeprowadzone badania metalograficzne spiekanych stali wykazały istnienie niejednorodnej i porowatej mikrostruktury spieków. Zaobserwowano również znaczne odwęglenie stali przy powierzchni badanych spieków.

EN

The present work was focused on the determination of transformation temperatures during sintering Mn-Cr-Mo PM structural steels based on pre-alloyed Astaloy CrL and Astaloy CrM powders. Manganese (3 %) and carbon (0.3 %) were added in the form of low-carbon ferromanganese and graphite C-UF powders, respectively. Mixtures of powders were prepared in Turbula mixer for 30 minutes. Following pressing in rigid die, rectangular test bars (5 × 5 × 15 mm) were sintered in Netzsch 402E dilatometer under different conditions. During dilatometric investigations of Fe-3%Mn-(Cr)-(Mo)-0.3%C the Ps, Bs and Ms temperatures were in the range of 600-650 degrees of Celsius, 450-500 degrees of Celsius and 200-300 degrees of Celsius respectively. Metallography of sintered steels showed inhomogeneous and porous microstructure; also decarburisation effect was observed.

8

Kinetyka i morfologia produktu przemiany bainitycznej w obszarze zbliżonym do Ms

Woźniak T. Z.

Archiwum Nauki o Materiałach

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2002

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T. 23, nr 4

351-374

PL

Wykonano badania dylatometryczne podczas hartowania stali węglowej z przemianą izotermiczną w temperaturach zbliżonych do Ms oraz badania uzupełniające z zastosowaniem analizy ilościowej. Na podstawie otrzymanych krzywych kinetycznych przemiany austenitu, w temperaturach 403-523 K, sporządzono wykres CTPi. Wyznaczono energię aktywacji we wszystkich charakterystycznych zakresach. W obszarze bainitu dolnego BD otrzymano dwa różne poziomy energii aktywacji, co jest spowodowane zmianami w kinetyce wzrostu i zarodkowania ferrytu podczas postępu przemiany. Zaobserwowano morfologię butterfly w zakresie występowania bainitu dolnego z midribem - BDM. Z występowaniem tej morfologii związane jest odchylenie od praw termodynamiki. Wykazano, że klasyczne metody obliczania energii aktywacji przemiany bainitycznej prowadzą do całkowitego pominięcia początkowych etapów przemian w niższych temperaturach oraz etapu końcowego w wyższych temperaturach. Potwierdzono przydatność zastosowania równania Johnsona-Mehla do opisu wzajemnie nakładających się na siebie przemian fazowych, w obszarze niskotemperaturowych zmian w kinetyce przemiany bainitycznej.

EN

Dilatometric investigations were carried out during isothermal transformation in high-carbon steel in the vicinity of M, and complementary research with quantitative analysis was made. A time-temperature-transformation diagram was drawn on the base of kinetic curves of austenite transformation at temperatures 403-523 K. Activation energies in all characteristic ranges were determined. Two separate levels of activation energy were found in the area of lower bainite - BD, which is related to a change in growth rates and nucleation rates of bainitic ferrite during advancement of the reaction. A butterfly morphology has been observed in the range of lower bainite with midrib - BDM. The occurrence of this morphology entails deviation from thermodynamics law. It was found that the classical methods used to calculate activation energy would totally neglect the initial ranges of transformations at lower temperatures and the final range at upper temperatures. The application of Johnson-Mehl equation was confirmed as useful to describe mutually overlaying fragments of phase transitions in the range of swing back.